Indian Strategic Studies: When will the COVID-19 pandemic end?

1 May 2021

When will the COVID-19 pandemic end?

By Sarun Charumilind, Matt Craven, Jessica Lamb, Adam Sabow, and Matt Wilson

This article updates our perspectives on when the coronavirus pandemic will end to reflect the latest information on vaccine rollout, variants of concern, and disease progression. In the United Kingdom and the United States, we see progress toward a transition to normalcy during the second quarter of 2021. The new wave of cases in the European Union means that a similar transition is likely to come later there, in the late second or third quarter. Improved vaccine availability makes herd immunity most likely in the third quarter for the United Kingdom and the United States and in the fourth quarter for the European Union, but risks threaten that timeline. The timeline in other countries will depend on seven crucial variables. And when herd immunity is reached, the risks will not vanish; herd immunity may prove temporary or be limited to regions in a country.

The fall in COVID-19 cases across much of the world over the past ten weeks signals a new dawn in the fight against the disease. Vaccines are proving effective and rapidly scaling, bending the curve in many geographies. This is a fragile dawn, however, with transmission and deaths still high, unequal access to vaccines, and variants of concern threatening to undo progress to date.

The trajectory of UK and US cases has enabled the beginnings of a transition toward normalcy,1 the first and more important of the pandemic’s two endpoints. We expect this transition to continue in the second quarter of 2021 and will likely see many aspects of social and economic life return to the prepandemic normal, consistent with UK Prime Minister Johnson’s staged reopening plan for the United Kingdom2 and US President Biden’s goal of a normal Independence Day.3 We are more confident in this timeline for the United Kingdom than for the United States, given that the first has already experienced a wave driven by a more infectious variant, whereas the latter could still face one. Parts of the European Union have recently faced setbacks: fewer doses in arms than in the United Kingdom or United States, a new wave of cases, and new lockdowns. A transition toward normalcy is mostly likely in Europe during the late second or third quarter of 2021. The timing will probably vary by country, depending on accelerating vaccine supplies, the impact of vaccinations on hospitalization rates, and the occurrence (or not) of new waves driven by new variants.

Herd immunity, the second endpoint, is most likely in the third quarter for the United Kingdom and the United States and in the fourth quarter for the European Union, with the difference driven by a more limited vaccine availability in the European Union. However, the risks to these timelines are real—herd immunity may not be achieved by the end of the year if vaccine hesitancy is high, if countries experience disruptions in vaccine supply, or if a variant that renders existing vaccines less effective spreads widely. And herd immunity may look different in different parts of the world, ranging from strong nationwide or regional protection to temporary or oscillating immunity to some countries not reaching herd immunity over the medium term.

In this article, we’ll review the developments since our last perspective (January 21), offer an outlook for each of the three geographies, assess risks, and outline what the end of the pandemic might look like.

Recent developments and their impact on timelines

The past month or two have seen seven important developments:

Vaccines work. We have growing evidence that vaccines are effective, as real-world data from Israel and the United Kingdom validate the clinical-trial results by showing a sharp reduction in hospitalizations and deaths.4 Emerging evidence also indicates that vaccines likely reduce transmission considerably, though not to the same degree that they prevent severe disease.5

The vaccine rollout is improving. Massive inoculation programs have accelerated, especially in the United Kingdom. As of March 15, the United Kingdom has administered 39 doses per 100 people in the total population; the corresponding figures for the United States and the European Union are 33 and 12 per 100, respectively.6 Just as important: sentiment about vaccine adoption is improving.7

More vaccines are coming. Johnson & Johnson’s one-shot vaccine appears to be highly effective against severe COVID-19 and received Emergency Use Authorization in the United States on February 27.8 Novavax’s vaccine is now in Phase III trials; preliminary results suggest it was highly effective in the United Kingdom but less so in South Africa.9 All of that makes it increasingly clear that the United Kingdom and the United States will have enough doses to vaccinate all adults by the end of the second quarter, and Europe should achieve the same milestone by the end of the third quarter, assuming no major vaccines are withdrawn. Further, vaccine trials on children aged 12 and up are well underway, and new trials on babies and children six months and older raise the possibility of pediatric vaccination, which would add to the population that could potentially contribute to herd immunity.10

Therapeutics are poised to make more of a difference. A new wave of COVID-19 therapeutics, including those from Eli Lilly,11 Merck–Ridgeback,12 and Vir Biotechnology,13 have produced positive data or received Emergency Use Authorization. The emerging data from these treatments suggest they have the potential to materially reduce hospitalizations and deaths for cases that do occur, accelerating a transition toward normalcy.

New cases and deaths are lower—but still high. New cases, hospitalizations, and deaths have dropped dramatically—by 79 percent and 89 percent, respectively, in the United States and the United Kingdom from the January peak, as of March 15.14 This trajectory has amplified discussions of a transition toward normalcy in both countries. The bend in the curve is fragile, however. Much of the decline in Europe has followed strict lockdowns; but lockdowns and other nonpharmaceutical interventions are still confoundingly difficult to get right, and even now, multiple European countries are experiencing upward case trends. And US deaths are still averaging 1,000 per day, many times higher than average daily flu deaths.15

It is increasingly clear that more infectious variants of concern16 may drive a new wave of cases in the coming months. The United Kingdom is in a relatively favorable position; cases are declining in spite of the high prevalence of the B.1.1.7 variant, suggesting that the country has a demonstrable ability to control the spread of more infectious variants. In contrast, the United States and parts of the European Union appear to have an increasing prevalence of B.1.1.7.17 The potential for a variant-driven wave of US cases and ongoing spread in Europe in the coming months is real.

Variants may also reduce vaccine efficacy or enable reinfection. Data from the AstraZeneca vaccine trial in South Africa highlight the potential for variants such as B.1.351 and P.1 to reduce the efficacy of vaccines.18 Other vaccine data, including those from Novavax and Johnson & Johnson, show a more modest reduction in efficacy, especially against severe disease caused by these variants.19 There is also early evidence of mutations arising independently in the United States that may reduce the efficacy of vaccines.20 These variants also appear to be more infectious than the original wild-type strain. These initial findings are based on very small sample sizes and may change as more information becomes available; we still do not know the impact of vaccines against severe disease from these strains. But if these results hold up, the spread of strains against which existing vaccines are substantially less effective would be a significant risk to lives and could delay the end of the pandemic.

What’s the net impact of all these developments? The data continue to indicate, as stated in our earlier perspectives, that a significant transition toward UK and US normalcy will occur in the second quarter of 2021, although the potential for a variant-driven wave in the United States is real and would blunt the transition (Exhibit 1). Potential herd-immunity timelines are bifurcating as a result of growth in variants that may reduce vaccine efficacy. If the variants turn out to be a minor factor (they only reduce vaccine efficacy modestly, or they don’t spread widely), then herd immunity in the second half of the year is likely for both countries—and is more likely in the third quarter than the fourth. However, if the impact of these variants is significant, we could see timelines significantly prolonging into late 2021 or beyond.

Exhibit 1

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How does this vary by geography?

Most of our analysis in this series has focused on the United Kingdom and the United States, which continue to move down a similar path. The end of Europe’s pandemic may come somewhat later, and other countries’ outlooks will depend on several variables.

European Union. Here, as in other regions, the timing of access to vaccines will be the biggest driver of the end of the pandemic. Levels of natural immunity from prior infection vary within the European Union but are generally in the same range as in the United Kingdom and the United States.21 Seasonality is likely to work in similar ways. And public interest in vaccination appears to be similar too, even in countries such as France, where interest in vaccination was significantly lower than in other countries in the region but may now be improving.22 The prevalence of the more infectious B.1.1.7 variant varies by country; most countries with cases are between the high UK levels and lower US levels.

Exhibit 2 lays out the likely timing of vaccine availability in the European Union. Broadly speaking, availability will be similar to that of the United Kingdom and the United States, but EU countries may need to wait a few months longer to vaccinate all adults. Please note that this would be subject to change and further delay if the Oxford–AstraZeneca vaccine remains suspended in multiple countries following concerns about blood clots; WHO has confirmed its continued support of the vaccine.23

Exhibit 2

Given that sufficient vaccine doses are available to vaccinate the highest-risk populations in the coming months, we expect to see the EU transition to normalcy during the second quarter of the year, although the start of this transition may be delayed until late in the quarter by a new wave of cases in some countries. A key difference for the European Union, as compared with the United Kingdom and the United States: herd immunity is more likely in the fourth quarter than the third quarter, given the likely timeline of vaccine delivery (Exhibit 3).

Exhibit 3

Rest of the world. While the European Union, the United Kingdom, and the United States have had broadly similar COVID-19 experiences, other parts of the world look very different. Countries like New Zealand have avoided significant COVID-19-associated mortality but appear to be further from herd immunity because so few New Zealanders have infection-driven immunity to SARS-CoV-2. On the other hand, if vaccine uptake is fast, New Zealand might achieve a longer-lasting vaccine-based herd immunity. A second factor is seasonality: the timing of seasonality-driven changes will be different in tropical locations and the Southern Hemisphere. A third is demographics: while the younger populations of many lower-income countries have led to lower COVID-19-associated mortality, they also make it harder for adult-only vaccination programs to drive herd immunity. And perhaps most importantly for timelines, access to vaccines is unequal. While COVAX and other access initiatives are working to close the gap, many low-income countries may not receive enough doses to vaccinate all adults until well into 2022.24 The world is on pace to manufacture enough doses for 80 percent of the global population—or close to 100 percent of the adult population—by the end of 2021, but the distribution of these doses may continue to be asymmetric.

Exhibit 4 provides a global view of seven factors that are likely to drive herd-immunity timelines for the rest of the world. These factors include the following:

Population vaccinated—the proportion of people who have received the vaccine so far

Vaccine courses secured—the additional supplies for which a country has contracted

Supply-chain readiness

Consumer vaccine sentiment—the public’s willingness to be vaccinated

Population under 19 years of age—a greater proportion of children makes a transition toward normalcy easier to achieve but herd immunity more difficult

Natural immunity, or the rate of prior COVID-19 infection—higher historical infection rates decrease the vaccination rate needed to achieve herd immunity

Prevalence of variants of concern

Exhibit 4

Risks to herd immunity

Herd immunity requires that enough people be simultaneously immune to SARS-CoV-2 to prevent widespread ongoing transmission. While data indicate that the most likely scenario is to reach this state on the timelines described above, five risks could delay progress.

First, vaccine adoption may prove lower than expected. That could happen if a real or perceived safety issue increases hesitancy or if younger populations see little reason to be vaccinated once older cohorts are protected and a transition toward normalcy is well underway. Second, herd immunity relies on the efficacy of vaccines at reducing transmission (rather than the usually reported efficacy at preventing disease in the vaccinated person). While initial data suggest that COVID-19 vaccines do block significant transmission,25 the efficacy rate may not prove high enough to drive herd immunity. Third, the duration of vaccine-mediated immunity may prove shorter than anticipated, making it hard to reach the necessary threshold for simultaneous immunity. Fourth, supply-chain disruptions and delays are real, and could produce supply shocks and interfere with timelines. Fifth, and most concerning, variants that reduce the efficacy of vaccines or the benefits of natural immunity may spread widely. Some initial data offer concerning evidence that B.1.351 and P.1 may be examples of such variants, although recent Novavax data (with a small sample size) offer some reassurance that its vaccine is effective against severe disease caused by B1.351.26 Similarly, limited data from the Pfizer-BioNTech and AstraZeneca vaccines show evidence of some protection against P.1.27

These five factors combined mean that there is still a meaningful chance that herd immunity is not reached in the medium term.

From theory to practice: What the ‘end’ might look like

The pandemic’s two endpoints, a transition toward normalcy and herd immunity, may look different in different places. As the name implies, a transition will include a series of steps that will gradually normalize aspects of social and economic life. The order and pace of these steps will vary by geography. Not everyone will immediately resume all of their prepandemic activities; rather, there will be a noticeable shift toward more of them. Steps may include a return to fully in-classroom education, fewer restrictions on the operations of bars and restaurants, more gatherings with larger groups of people, the reopening of offices, and fewer prohibitions on interregional or international travel. The United Kingdom’s plan for reopening provides an example of the stepwise manner in which a transition to normalcy is likely to occur.28

Herd immunity will represent a more definitive end to the pandemic. Isolated cases may still occur—indeed, the virus may continue to circulate for one or more quarters after herd immunity is reached. But with herd immunity, population-wide public-health measures can be phased out. As populations get closer to this state, it may be helpful to introduce some nuance to what we mean by the term.

Nationwide herd immunity. The full population is well protected so that the country experiences, at most, occasional small flare-ups of disease. This scenario is most likely in smaller countries where immunity to COVID-19 can become uniformly high.

Regional herd immunity. Some regions, states, or cities are well protected, while others experience ongoing outbreaks of COVID-19. In large, diverse countries like the United States, this situation is especially easy to imagine.

Temporary herd immunity. A population or region achieves herd immunity for some period, but as variants are introduced, against which prior immunity is less effective, a new wave of cases is launched. Another potential trigger for such a wave could come as immunity (particularly natural immunity) wanes. As the number of new cases of COVID-19 falls globally, the rate of emergence of important variants should also decrease, but some risk will remain.

Endemicity. A region fails to achieve herd immunity. Endemicity is most likely in places where vaccine access is limited, where few people choose to be vaccinated, if the duration of immunity is short, or variants that reduce vaccine efficacy are common and widespread. Endemicity might include cyclic, seasonal waves of disease, broadly similar to the flu, or a multiyear cycle of resurgence.

The next few years are likely to see a combination of some or all of these options around the world. Given the likely timing of herd immunity in various geographies and the uncertain duration of protection from vaccines (both duration of immune response and efficacy versus new variants), it is likely that some measures such as booster vaccines are likely to be required indefinitely. Herd immunity is not the same as eradication. SARS-CoV-2 will continue to exist. Even when a country reaches herd immunity, ongoing surveillance, booster vaccines, and potentially other measures may be needed.

A year ago, the world was coming to terms with a long, difficult journey ahead. Twelve months later, the end of the pandemic is in sight for some parts of the world. It’s much too soon to declare victory, however. We hope that our perspectives prove useful to leaders as they set policy and strategy; we will continue to update the series.

Sarun Charumilind and Jessica Lamb are both partners in McKinsey’s Philadelphia office, Matt Craven is a partner in the Silicon Valley office, Adam Sabow is a senior partner in the Chicago office, and Matt Wilson is a senior partner in the New York office.

The authors wish to thank Xavier Azcue for his contributions to this article.

This article updates our earlier perspectives on when the coronavirus pandemic will end. Transition toward normalcy in the United States remains most likely in the second quarter of 2021 and herd immunity in the third and fourth quarters, but the emergence of new strains and a slow start to vaccine rollout raise real risks to both timelines. We also add a perspective for the United Kingdom.

The past five weeks have brought an array of conflicting news on the COVID-19 pandemic, affecting our estimates about when the coronavirus pandemic will end. Margaret Keenan, a British nonagenarian, made history on December 8 by becoming the first person to receive the Pfizer-BioNTech vaccine for SARS-CoV-2 outside a clinical trial.29 Since then, several other vaccines have been authorized for use around the world. Sufficient doses are likely to be available to vaccinate high-risk populations in the United States in the first half of 2021. In parallel, however, more-infectious strains of the virus have been detected in South Africa, the United Kingdom, and elsewhere and have spread to an increasing number of countries.30 And the initial rollout of vaccines has been slower than hoped in many places.31

While the United States could still achieve herd immunity in the third or fourth quarter of 2021 (in line with the peak probability in our previous estimates), the emergence of more-infectious variants of SARS-CoV-2 increases the risk that this milestone will not be achieved until later. More-infectious viruses require that a higher percentage of people be simultaneously immune to reach herd immunity.32 While a more infectious variant likely means more people are acquiring natural immunity through infection (despite ongoing efforts to minimize new cases), the net impact of more-infectious strains is likely to be that a higher portion of the population needs to be vaccinated, which may take more time.

We still believe that the United States can transition toward normalcy during the second quarter of 2021, but the same risks also threaten this timeline. A transition toward normalcy would be driven by a combination of seasonality aiding a decline in cases and early vaccine doses helping reduce mortality by protecting those at greatest risk of serious illness. As COVID-19’s impact on health wanes, we are likely to see greater normalization of social and economic life. Data on the availability of vaccine doses in the United States increase confidence that this is possible, but the slow start to the vaccine rollout reinforces that success is by no means guaranteed.

This article describes “most likely” timelines for when the coronavirus pandemic will end. It is now harder to imagine the United States or United Kingdom transitioning to normalcy before second quarter 2021 or reaching herd immunity before third quarter 2021. But a number of other factors could delay the timelines beyond those described, including unexpected safety issues emerging with early vaccines, significant manufacturing or supply-chain delays, continued slow adoption, further mutation, or a shorter-than-anticipated duration of vaccine-conferred immunity. Herd immunity will also require vaccines to be effective in reducing transmission of SARS-CoV-2, not just in protecting vaccinated individuals from getting sick. This is likely, but has not yet been proven at scale.33

Herd immunity

More-infectious strains raise the bar

Herd immunity to a pathogen is achieved when a sufficient portion of a population is simultaneously immune to prevent sustained transmission. The threshold to achieve it is governed by a number of factors, including the transmissibility of the disease.34 More-infectious strains of SARS-CoV-2 therefore raise the bar on herd immunity. The virus has been mutating since it was identified a year ago. The concerning development in recent weeks has been the confirmation of new strains in South Africa, the United Kingdom, and elsewhere that combine multiple mutations and have different profiles. While data are still emerging, initial estimates suggest that the transmissibility rate of the UK strain is 40 to 80 percent higher than that of the original SARS-CoV-2 strain, and that transmission rates could be higher among children too.35 36 There is no evidence of higher case fatality with either new strain, but there are fears that new strains may affect how antibodies bind to the virus and may reduce the efficacy of vaccines or antibody treatments developed over the past few months. More data are likely to emerge on this in the weeks ahead.

If these strains become dominant, they may cause a material delay in reaching herd immunity. While many people are acquiring natural immunity through infection, variants with enhanced transmissibility, if they predominate among all strains, could increase the proportion of people who need to be simultaneously immune to achieve herd immunity by ten to 20 percentage points, and increase vaccine coverage levels needed to 65 to 80 percent of the population (or 78 to 95 percent of those over 12 years old).37 More detail is shown in Exhibit 1 below.

Vaccinating more people is a nonlinear challenge. Consumer surveys suggest that a portion of the population is cautious about vaccination. Increasing coverage from 70 to 80 percent is therefore harder than increasing from 60 to 70 percent. Because more-transmissible variants raise herd-immunity thresholds, there will also be less tolerance for low vaccine effectiveness. For example, with a variant that is 40 to 80 percent more transmissible, vaccine efficacy of 90 percent would require 83 to 100 percent of those over 12 to be vaccinated; efficacy of anything less than 75 percent would make herd immunity likely unachievable through vaccination of only those over 12.

While the variant of concern appears to be most widespread in the United Kingdom, it has been detected in over 30 countries, many of which (including the United States) have limited capacity for genetic sequencing. As a result, we may be significantly underestimating its spread.38 39 The strain is likely to continue spreading in the coming months, propelled by its reproductive advantage over the original. This appears to have occurred in southern England over the past few months. If new strains predominate, they could lead to a longer timeline to herd immunity.

Vaccine rollout: A slow start, but there is still time to improve

The speed of COVID-19 vaccine development has been an unqualified success. The approval, in at least one country, of vaccines made by Pfizer and BioNTech, Moderna, Oxford and AstraZeneca, Sinopharm, Serum Institute, Bharat Biotech, Gamaleya, and others within a year of viral sequencing smashed all records for development timelines. But rollout is off to a slow start. While countries such as Israel have shown what is possible, the United States has fallen behind its targets.40 41 It is still early days, and there is time to accelerate, but there is little margin for error if the United States is to achieve herd immunity in third quarter 2021. In addition, not all regions are adhering closely to manufacturer dosing protocols—for example, delaying second doses or giving a first dose from one manufacturer followed by a second from another—and the impact of that is unclear. These approaches could reduce mortality in the short term by broadening access, but they could also delay herd immunity if, for example, a delayed second dose reduces efficacy. It’s also possible that once most people in the highest-risk groups have received vaccinations, the pace of vaccination will slow if lower-risk groups do not embrace the opportunity.

We believe that herd immunity in the United States is still most likely in third or fourth quarter 2021, but that the chance of delay until first quarter 2022 or beyond has increased (Exhibit 2). There is relatively little chance of achieving herd immunity before then. Even later herd immunity remains possible if other challenges arise, especially vaccine safety concerns or ambivalence to vaccination following a transition toward normalcy. This potential delay represents a call to action for policy makers, both in terms of the pace of the vaccine rollout and how new strains are managed.

Exhibit 2

More-transmissible variants and slower initial vaccine rollout increase downside risk to the Q3–Q4 2021 timeline to achieve herd immunity.

Chart: Probability of herd immunity1 to COVID-19 pandemic for the United Kingdom and United States2 by quarter (illustrative)

Two skewed bell curves estimate when herd immunity will occur.

11/23/20 estimate. From Q4 2020 to Q1 2021 the probability of herd immunity is negligible. The curve rises sharply from Q1 2021 to a peak between Q3 and Q4 2021. The long tail of the curve shows falling probabilities to Q3 2023 and beyond.

1/15/21 estimate. The start, peak, and tail of this curve are almost the same as the previous one. A flatter curve indicates herd immunity will probably occur one month later.

Early herd immunity if:

Vaccine rollout and adoption are faster than expected

Natural immunity is significantly higher than realized

More-transmissible variants lead to higher rates of natural immunity

Peak probability of herd immunity driven by:

US Biologics License Applications (BLA) with full approval by March/April 2021 or earlier

Approximately 3–9 months for manufacturing, distribution, and sufficient adoption to reach herd immunity

Later herd immunity if one or more of the following occur:

Safety issues delay BLA

Manufacturing/supply-chain issues slow rollout

More-infectious variants raise the threshold for achieving herd immunity

Adoption is slower than anticipated

Duration of immunity is short

Vaccine prevents disease progression but does not meaningfully reduce transmission

Notes

1Herd immunity is achieved when a sufficient portion of a population is simultaneously immune to prevent sustained transmission. At this point, significant, ongoing public-health measures are not needed to prevent future spikes in disease and mortality (this might be achieved while there are still a number of people in particular communities who still have the disease, as is the case with measles).

2Timeline to functional end is likely to vary somewhat based on geography.

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Increasing recognition of medium-term endemicity

While many parts of the world are expected to reach herd immunity against COVID-19, there is increasing consensus that globally, SARS-CoV-2 is likely to remain endemic in the medium term. David Heymann, the chairman of the World Health Organization’s Strategic and Technical Advisory Group for Infectious Hazards, noted in December that endemicity may be the “destiny” of this virus.42 This might make COVID-19 analogous to measles—a disease that causes intermittent, limited outbreaks in countries with well-developed vaccination programs but significant ongoing disease in parts of the world where access to vaccines is more limited. It is also possible that COVID-19 will be seasonal, with predictable annual peaks in parts of the world where it is endemic.43

Transition toward normalcy

A transition toward normalcy will occur when COVID-19 mortality falls and the disease is de-exceptionalized in society. COVID-19 will not disappear during this transition, but will become a more normal part of the baseline disease burden in society (like flu, for example), rather than a special threat requiring exceptional societal response. During this transition, controlling the spread of SARS-CoV-2 will still require public-health measures (such as continued COVID-19 testing and mask use in many settings), but mortality will fall significantly, allowing greater normalization of business and social activities. This will be driven by a combination of early vaccine rollout (which, being directed first at those at greatest risk, should reduce deaths faster than cases), seasonality, increasing natural immunity, and stronger public-health response.

Increasing clarity on the availability of vaccine doses during the first half of 2021 in the United States improves the odds of an early transition toward normalcy. As Exhibit 3 shows, Pfizer and Moderna are expected to deliver sufficient vaccine doses to vaccinate all high-risk Americans during the first half of the year. This does not account for other vaccines that are likely to become available, including those approved in other markets (for example, Oxford-AstraZeneca) or others that are likely to report clinical trial data in the first quarter of 2021 (including Johnson & Johnson and Novavax). Older people are generally more willing to be vaccinated than the general population. However, slow initial rollout of the vaccines and the spread of more infectious variants increase the risk that significant mortality continues in the second quarter, blunting a transition to normalcy.

Exhibit 3

In the United States, doses committed by Pfizer and Moderna by July 31 are approximately enough for population in phases 1a–c.

Estimate of supply needed, doses1 for US population in phases 1 and 24

48 million for phase 1a

98 million for phase 1b

56 million for phase 1c: ages 65–74 (through 3/31/21)

202 million for phase 1c: other (4/1/21–7/31/21)

~160 million for phase 2 (2021 Q3/4)

Total ~560 million

Estimate of supply available

Delivery deadlines for vaccines with Emergency Use Authorization in the United States, millions of doses1 (illustrative)CompanyBy 3/31/21Between 4/1/21 and 6/30/21Between 7/1/21 and 7/31/21Total by 7/31/212021 Q3/4

Pfizer 100 70 30 200

Moderna 100 100 200

Total of Pfizer and Moderna 200 170 30 400

Potential AstraZeneca, J&J, and Novavax doses2 unspecified additional number

Options to purchase3 300 Pfizer, 400 Moderna

Notes

1Two doses needed per person.

2Subject to regulatory authorization.

3Timing not specified.

4According to CDC ACIP interim recommendations (December 22, 2020), will vary as individual states are making their own decisions (CDC phase 1a = healthcare personnel, long-term care facility residents; CDC phase 1b = frontline essential workers, persons aged ≥75 years; CDC phase 1c = persons aged 65–74 years; persons aged 16–64 years with high-risk medical conditions; essential workers not recommended for vaccination in phase 1b); phase 2 estimate based on 2019 census population estimate of persons aged ≥16, less population accounted for in CDC estimates of persons covered in phases 1a–c; CDC and Operation Warp Speed vaccination guidelines may evolve over time.

Source: Bloomberg; DC; HHS; Moderna; Pfizer; Reuters; WSJ

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Taking these variables into account, we still believe that a transition toward normalcy is likely during second quarter for the United States, but that downside risks have increased. If early vaccine doses reach a significant percentage of high-risk elderly individuals by the end of quarter one, the combination of protecting these groups and the arrival of spring in the northern hemisphere should improve the situation compared with where the United States is now. Depending on vaccination progress over the summer (whether the United States is on the earlier or later end of the herd immunity window), there may be a smaller fall wave of disease in third to fourth quarter 2021.

While the potential for a transition toward normalcy in just a few months is encouraging, many signs suggest that the next six to eight weeks will be difficult. Case and death numbers are at or near all-time highs in many locations, new variants may accelerate short-term transmission, and vaccine rollout has not yet proceeded far enough to protect much of the population. Strong public-health measures will remain critical to saving lives during this period.

Timeline for the United Kingdom

We see similar dynamics in the United Kingdom. Three factors lead us to believe that timelines for herd immunity and transition toward normalcy in the United Kingdom will be similar to those in the United States. First, access to vaccines is sufficient to immunize a large percentage of both the US and UK populations during 2021. Second, public willingness to be vaccinated is generally similar between the two countries.44 Third, the fraction of US and UK residents who already have natural immunity from prior infection is in the same range (with significant variability among regions within countries).45

The variant of concern represents a potential source of difference. While it is known to be highly prevalent in the United Kingdom and present in the United States, there is a significant chance that it will predominate throughout the United States over the coming months. All else being equal, countries with a higher proportion of more-infectious variants—assuming they increase public-health measures to handle them—are likely to achieve herd immunity later.

We will add a perspective for other parts of the world, including the rest of Western Europe, in future updates to this article.

Twelve months ago, most people weren’t thinking about COVID-19. Today, much of the world is intensely focused on it, but we can reasonably expect the imminent threat to abate. Much work remains to be done. In the short term, public-health measures can help control the pandemic, but even when herd immunity is achieved, managing the risk of COVID-19 will require monitoring, potential revaccination, and treatment of isolated cases. Every country has its own COVID-19 story, but those stories will eventually reach some kind of ending.

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About the authors

The authors wish to thank Xavier Azcue, Brian Hencke, David Meredith, Michalis Michaelides, Anthony Ramirez, Virginia Simmons, Konstantinos Tsakalis, and Lieven Van der Veken for their contributions to this article.

November 23, 2020

Our November 23 update takes on the questions raised by recent news: When will vaccines be available? And is the end of COVID-19 nearer?

Since we published our first outlook, on September 21st, the COVID-19 pandemic has raged on, with more than 25 million additional cases and more than 400,000 additional deaths. While the situation looks somewhat better in parts of the Southern Hemisphere, much of Europe and North America is in the midst of a “fall wave,” with the prospect of a difficult winter ahead. Yet the past two weeks have brought renewed hope, headlined by final data from the Pfizer/BioNTech46 vaccine trial and interim data from the Moderna trial, both showing efficacy of approximately 95 percent47 ; and progress on therapeutics. Is an earlier end to the pandemic now more likely?

The short answer is that the latest developments serve mainly to reduce the uncertainty of the timeline (Exhibit 1). The positive readouts from the vaccine trials mean that the United States will most likely reach an epidemiological end to the pandemic (herd immunity) in Q3 or Q4 2021. An earlier timeline to reach herd immunity—for example, Q1/Q2 of 2021—is now less likely, as is a later timeline (2022). If we are able to pair these vaccines with more effective implementation of public-health measures and effective scale-up of new treatments and diagnostics, alongside the benefits of seasonality, we may also be able to reduce mortality enough in Q2 to enable the United States to transition toward normalcy. (See sidebar “Two endpoints” for our definitions.)

Exhibit 1

Sidebar

Two endpoints for the pandemic

A secondary effect of the recent vaccine trials is to make Q3 2021 more likely for herd immunity than Q4. That said, major questions are still outstanding, even about vaccines, such as long-term safety, timely and effective distribution, and vaccine acceptance by the population, to say nothing of lingering epidemiological questions such as the duration of immunity.

These are estimates for the United States, which is likely to have fast and ready access to vaccines. We will consider timelines for other countries in forthcoming updates; they will vary based on the timing of access and distribution of vaccines and other factors. In this update, we review the most recent findings, look deeper at five implications of the ongoing scientific research, and discuss why our timeline estimates have not shifted meaningfully.

Revelations from vaccine and antibody trials

The world has cheered announcements over the past two weeks by Pfizer and its partner BioNTech, and from Moderna. Their COVID-19 vaccine candidates are showing efficacy rates that are higher than many dared hope for. One is a final result, and the other is an initial result whose sample size is large enough to give reasonable confidence in the data. At about 95 percent, efficacy is higher than expected by most experts.[[Footnote 48] It exceeds the optimistic case that we included in our September article. Higher efficacy provides greater benefit to any vaccinated individual and may help to encourage uptake among some segments of the population. It also reduces the fraction of the population required to reach herd immunity. Moderna also announced that its vaccine is more shelf-stable than expected and would need only refrigeration to keep it stable for 30 days—another piece of good news. Finally, there are a number of other vaccines in late-stage trials from which data is expected in the coming months.

Caution is still warranted. The safety records of the Pfizer and Moderna vaccines appear promising so far (no serious side effects reported), but the coming months will provide a fuller picture as the sample size grows. We don’t yet know how long the protection the vaccines offer will last. The Pfizer trial has enrolled some children (ages 12 and older), but efficacy in those under 18 remains unclear.

Beyond vaccines, science is also progressing in therapeutics for COVID-19. For example, Eli Lilly’s antibody bamlanivimab was granted Emergency Use Authorization (EUA) by the US Food and Drug Administration on November 9,49 and Regeneron’s EUA for its antibody cocktail REGN-COV2 for EUA was approved on November 22. Emerging data on these antibodies suggest that they can reduce the need for hospitalization of high-risk patients, and hold potential for post-exposure prophylaxis.50 While they are not recommended for use in hospitalized patients, these antibodies add to the growing armamentarium of treatments and protocols for COVID-19, where every incremental advance could help to reduce mortality. Collectively, these treatments and changes in clinical practice have lowered mortality for those hospitalized by 18 percent or more.51

Looking deep into the data

Research and findings of the past two months have shed light on a number of uncertainties and in some cases have raised new questions. Here we review five implications; each has helped refine our probability estimates for the COVID-19 pandemic timeline.

Vaccine age restrictions elevate coverage requirements to reach herd immunity

It appears that the two vaccines mentioned will be indicated first for use in adults.52 It’s not clear when use in children will be indicated. One consequence is that the vaccines’ contribution to population-wide herd immunity will depend on adults, at least until vaccines are approved for use in younger populations. If vaccines are efficacious, safe, and distributed to all ages, vaccine coverage rates of about 45 to 65 percent—in combination with projected levels of natural immunity—could achieve herd immunity (Exhibit 2).

Exhibit 2

On the other hand, if vaccines are efficacious but distributed only to adults, who comprise only 76 percent of the US population,53 then higher vaccine coverage rates—approximately 60 to 85 percent—could be required to achieve herd immunity.

Another consequence is that older children, who have twice the COVID-19 incidence of younger children and who have higher viral loads (and therefore greater potential contagiousness) than adults54 may not have immediate access to vaccines.

We recognize that calculating herd immunity thresholds is complex. Basic formulas fail to account for variations in the way populations interact in different places.55 For this reason we include relatively wide ranges.

Unclear impact of vaccines on transmission could raise the bar on coverage

Vaccine trials and regulatory approval will be based on safety and efficacy in reducing virologically confirmed, symptomatic disease among individuals.56 That’s not the same as reducing transmission. This distinction will have much to say about whether the United States reaches normalcy in Q2 or Q3 of 2021. In practice, we have data on whether people who are vaccinated are less likely to get sick with COVID-19 (and less likely to get severe disease), but we won’t have data on how likely they are to transmit to others. It’s an important distinction because what will drive herd immunity is reduction in transmission. If vaccines are only 75 percent effective at reducing transmission, then coverage of about 60 to 80 percent of the population will be needed for herd immunity. And if a vaccine is only 50 percent effective at reducing transmission, coverage of over 90 percent would be required (Exhibit 3).

Exhibit 3

Wide variations in local seroprevalence suggest heterogeneous paths to herd immunity

Improved estimates of seroprevalence are increasingly available for many regions. They vary widely, from as low as 1 to 2 percent in some states like Colorado and Kansas to 14 to 20 percent in New Jersey and New York.57 Because achieving herd immunity relies in part on a population’s natural immunity, it appears that some locations are closer to herd immunity than others (and have likely also experienced worse impact on public health to date.) Based on a range of likely vaccine scenarios and the fact that those with prior exposure to SARS-CoV-2 will still be eligible for vaccination, every ten percentage-point increase in seroprevalence could roughly translate into a one-month acceleration of the timeline to the epidemiological endpoint.

However, it is possible that areas with higher seroprevalence may also have higher thresholds for herd immunity, because their populations may mix more,58 which could have contributed to higher seroprevalence to begin with. If that’s true, then while they are further along, they may also have further to go. Well-executed distribution of effective vaccines will still be paramount.

Potentially shorter duration of immunity could prolong the path to the ‘end’

Earlier in the pandemic, it was unclear how long immunity after COVID-19 infection would last. Duration of immunity matters, obviously; for instance, our modeling suggests that if natural immunity to COVID-19 lasts six to nine months, as opposed to multiple years (like tetanus) or lifelong (like measles), herd immunity is unlikely to be achieved unless adult vaccination rates approach 85 percent. While COVID-19 reinfection is documented but rare, there are now population-level studies that question the durability of immunity. Antibody levels may wane after just two months, according to some studies, while a United Kingdom population-monitoring effort reported that antibody prevalence fell by 26 percent over three months.59 The relationship between waning antibodies and reinfection risk remains unclear. Other research suggests that even with waning levels of COVID-19 antibodies, the immune system may still be able to mount a response through other specific B-cell and T-cell immune pathways, where emerging evidence shows much greater durability after six months.60

Manufacturing and supply issues are clearer, but have not vanished

If the initial efficacy data from the Pfizer and Moderna vaccine trials hold up, and if no significant safety issues emerge, then initial demand is likely to be high. Two promising candidates are better than one, but supplies will undoubtedly be constrained in the months following EUA and approval. The situation may be dynamic as vaccines are approved at different times, each with its own considerations in manufacturing and distribution. For example, current data suggest that Moderna’s vaccine is stable at refrigerated temperatures (2 to 8 degrees Celsius) for 30 days and six months at –20 degrees Celsius. Pfizer’s vaccine can be stored in conventional freezers for up to five days, or in its custom shipping coolers for up to 15 days with appropriate handling. Longer-term storage requires freezing at –70 degrees Celsius, requiring special equipment.61 Both Pfizer’s and Moderna’s would be two-dose vaccines, necessitating rigorous follow-up for series completion. These and other complexities create risk of delay. Timelines to reach the desired coverage threshold will be affected by health systems’ abilities to adapt to changing needs and updated information.

The pandemic’s end is more certain, and may be a little nearer

Given all of these variables, where do we net out?

While the winter of 2020/2021 in the Northern Hemisphere will be challenging, we are likely to see mortality rates fall in Q2 (or possibly late Q1) of 2021. Seasonality and associated changes in behavior will begin to work again in our favor in the spring, and the combination of early doses of vaccines targeted to those at highest risk (and the benefits of the Pfizer and Moderna vaccines in reducing severe disease), advances in treatment, expanded use of diagnostics, and better implementation of public-health measures should serve to significantly reduce deaths from COVID-19 in the second quarter. At this stage, when monthly mortality from COVID-19 may start to resemble that of flu in an average year, we may see a transition toward normalcy, albeit with public-health measures still in place.

We are as excited as others about the stunning developments in vaccines. We think Q3 or Q4 of 2021 are even more likely to see herd immunity in the United States. This is based on EUA of one or more high-efficacy vaccines in December 2020 or January 2021, as manufacturers are targeting62 ; distribution to people at highest risk (healthcare workers, the elderly, and those with comorbidities) in the early months of 202163 ;full approval of a vaccine in March or April; and then widespread rollout. Our estimates of three to eight months for manufacturing, distribution, and adoption of sufficient vaccine doses to achieve herd immunity remain unchanged, and suggest that the milestone may be reached between July and December 2021.

Recent developments suggest that herd immunity is less likely to come in early 2021, given that vaccines are arriving roughly on the expected timeline; and the downside scenario stretching into 2022 is also less likely, since efficacy is clearer. The new vaccines may slightly accelerate the timeline—the ongoing surge in cases will likely continue into winter, which would increase natural immunity levels going into Q2. Further, higher-than-expected efficacy may help offset coverage challenges that surveys have suggested. Those two factors could advance the timeline, and make Q3 a little more likely than Q4.

Our estimate is based on the widest possible reading of the current scientific literature and our discussions with public-health experts in the United States and around the world. It’s possible that unforeseen developments such as significantly more infections than expected this winter could lead to earlier herd immunity. And real downside risk remains, especially with respect to duration of immunity and long-term vaccine safety (given the limited data available so far). Herd immunity might not be reached until 2022 or beyond.

Even when herd immunity is achieved, ongoing monitoring, potential revaccination, and treatment of isolated cases will still be needed to control the risk of COVID-19. But these would fall into the category of “normal” infectious disease management—not the society-altering interventions we have all lived through this year. The short term will be hard, but we can reasonably hope for an end to the pandemic in 2021.

Download the article here.

About the authors

The authors wish to thank Gaurav Agrawal, Xavier Azcue, Jennifer Heller, Anthony Ramirez, Shubham Singhal, and Rodney Zemmel for their contributions to this article.

This article was edited by Mark Staples, an executive editor in the New York office.

September 21, 2020

Normalcy by spring, and herd immunity by fall? We assess the prospects for an end in 2021.

In 1920, a world wearied by the First World War and sickened by the 1918 flu pandemic desperately sought to move past the struggles and tragedies and start to rebuild lives. People were in search of a “return to normalcy,” as Warren G. Harding put it. Today, nearly every country finds itself in a similar position.

More than eight months and 900,000 deaths into the COVID-19 pandemic,64 people around the world are longing for an end. In our view, there are two important definitions of “end,” each with a separate timeline:

An epidemiological end point when herd immunity is achieved. One end point will occur when the proportion of society immune to COVID-19 is sufficient to prevent widespread, ongoing transmission. Many countries are hoping that a vaccine will do the bulk of the work needed to achieve herd immunity. When this end point is reached, the public-health-emergency interventions deployed in 2020 will no longer be needed. While regular revaccinations may be needed, perhaps similar to annual flu shots, the threat of widespread transmission will be gone.

A transition to a form of normalcy. A second (and likely, earlier) end point will occur when almost all aspects of social and economic life can resume without fear of ongoing mortality (when a mortality rate is no longer higher than a country’s historical average) or long-term health consequences related to COVID-19. The process will be enabled by tools such as vaccination of the highest-risk populations; rapid, accurate testing; improved therapeutics; and continued strengthening of public-health responses. The next normal won’t look exactly like the old—it might be different in surprising ways, with unexpected contours, and getting there will be gradual—but the transition will enable many familiar scenes, such as air travel, bustling shops, humming factories, full restaurants, and gyms operating at capacity, to resume.

The two ends are related, of course, but not linearly. At the latest, the transition to normal will come when herd immunity is reached. But in regions with strong public-health responses, normalcy can likely come significantly before the epidemiological end of the pandemic.

The timeline to achieve the ends will vary by location. In this article, we’ll explain the criteria that will be key factors in determining when each is reached. In the United States and most other developed economies, the epidemiological end point is most likely to be achieved in the third or fourth quarter of 2021, with the potential to transition to normalcy sooner, possibly in the first or second quarter of 2021. Every day matters. Beyond the impatience that most feel to resume normal life, the longer it takes to remove the constraints on our economies, the greater will be the economic damage.

The epidemiological end point

Most countries have deferred the hope of achieving herd immunity until the arrival of a vaccine. When herd immunity is reached, ongoing public-health interventions for COVID-19 can stop without fear of resurgence. The timing of the end point will vary by country and will be affected by a number of factors:

the arrival, efficacy, and adoption of COVID-19 vaccines—the biggest drivers in the timeline to herd immunity65

the level of natural immunity in a population from exposure to COVID-19; in our estimate, between 90 million and 300 million people globally may have natural immunity66

potential cross-immunity from exposure to other coronaviruses67

potential partial immunity conferred by other immunizations, such as the bacille Calmette–Guérin (BCG) vaccine for tuberculosis68

regional differences in the ways that people mix, which will produce different thresholds for herd immunity

Consider the first and most crucial variables: the arrival of vaccines, their efficacy, and their adoption. We see four plausible scenarios for vaccine efficacy and adoption, illustrated in Exhibit 1.69 Different combinations of those two factors will drive varying levels of conferred immunity, implying the extent of natural immunity that will be required to reach herd immunity under each scenario. Combinations of efficacy and adoption beyond those shown are possible.

Exhibit 1

The other variables will also have much to say about the timeline to reach herd immunity (see sidebar, “Key factors affecting the timeline to herd immunity”).

Sidebar

Key factors affecting the timeline to herd immunity

Based on our reading of the current state of the variables and their likely progress in the coming months, we estimate that the most likely time for the United States to achieve herd immunity is the third or fourth quarter of 2021. As we wrote in July 2020, one or more vaccines may receive US Food and Drug Administration Emergency Use Authorization before the end of 2020 (or early in 2021) and the granting of a Biologics License Application (also known as approval) during the first quarter of 2021.

Vaccine distribution to a sufficient portion of a population to induce herd immunity could take place in as few as six months. That will call for rapid availability of hundreds of millions of doses, functioning vaccine supply chains, and peoples’ willingness to be vaccinated during the first half of 2021. We believe that those are all reasonable expectations, based on public statements from vaccine manufacturers and the results of surveys on consumer sentiment about vaccines.70

Herd immunity could be reached as soon as the second quarter of 2021 if vaccines are highly effective and launched smoothly or if significant cross-immunity is discovered in a population (Exhibit 2). (For more on the potential for a faster resolution of the COVID-19 crisis in the United States, see “An optimistic scenario for the US response to COVID-19”.) On the other hand, the epidemiological end of the pandemic might not be reached until 2022 or later if the early vaccine candidates have efficacy or safety issues—or if their distribution and adoption are slow. At worst, we see a long-tail possibility that the United States could be still battling COVID-19 into 2023 and beyond if a constellation of factors (such as low efficacy of vaccines and a short duration of natural immunity) align against us.

Exhibit 2

The paths to herd immunity in other high-income countries are likely to be broadly similar to the one in the United States. The timelines will vary based on differences in vaccine access and rollout and in levels of natural immunity—and potentially, in levels of cross-immunity and previous coverage of other vaccines, such as the BCG vaccine. Even as some locations reach herd immunity, pockets of endemic COVID-19 disease are likely to remain around the world, for example in areas affected by war or in communities with persistently low adoption of vaccines. In such places, until herd immunity is reached, COVID-19 might be analogous to measles—not a day-to-day threat to most people, but a persistent risk. If immunity wanes—for example, if booster vaccines are not fully adopted—then COVID-19 could become more widely endemic.

The arrival of herd immunity won’t mean a complete end to all public-health interventions. It’s possible that regular revaccinations would be required to maintain immunity, and ongoing surveillance for COVID-19 will be required. But herd immunity would mean that the emergency measures currently in place in many countries could be lifted.

The pace at which governments relax public-health measures will be critical. Some of those measures (such as full lockdowns and restrictions on certain industries) have significant social and economic consequences, and others (such as testing and tracing), while expensive, don’t. Many governments are employing packages of measures that aim to minimize the number of COVID-19 cases and excess mortality while maximizing social and economic degrees of freedom.

The transition to normal

The second end point of the pandemic may be reached earlier than the first. We estimate that the mostly likely time for this to occur is the first or second quarter of 2021 in the United States and other advanced economies. The key factor is diminished mortality.

Society has grown used to tracking the number of COVID-19 infections (the case count). But case counts matter primarily because people are dying from the disease and because those who survive it may suffer long-term health consequences after infection. The latter is an area of scientific uncertainty, but there is concern that some recovered patients will face long-term effects.71

Most countries have made significant progress in reducing the numbers of deaths and hospitalizations associated with COVID-19. Some are close to eliminating excess mortality. Those results have generally been achieved through a combination of moderately effective interventions rather than a single “big bang” (Exhibit 3).

Exhibit 3

A transition to the next normal, in whatever form that takes, will come gradually when people have confidence that they can do what they used to do without endangering themselves or others. Gaining that confidence will require a continuation of the progress made to reduce mortality and complications, as well as further scientific study regarding long-term health consequences for recovered patients. When confidence is restored, people will again fill bars, restaurants, theaters, and sports venues to full capacity; fly overseas (except for the highest-risk populations); and receive routine medical care at levels similar to those seen prior to the pandemic.

The timing of such a transition will depend on the progress toward herd immunity, as previously detailed (since more people with immunity means fewer deaths and long-term health consequences), and on the effectiveness of a country’s public-health response. Transitions will be gradual. They have already begun in some locations and could be well advanced in most countries by the first or second quarter of 2021. Given the interconnectedness of the global economy, country timelines to normalcy are not fully independent of one another.

To achieve that, we will need to see significant progress on the epidemiological end point, including an effective vaccine receiving Emergency Use Authorization approval during the fourth quarter of 2020 or the first quarter of 2021, followed by a smooth rollout and adoption by high-risk populations. Favorable findings on natural and cross-immunity would help accelerate timelines. Five additional criteria will also contribute to the transition to a form of normalcy—the more of these that are achieved, the faster the milestone is likely to be reached:

continued improvement by governments in the application of public-health interventions (such as test and trace) that don’t significantly limit economic and social activities

compliance with public-health measures until we achieve herd immunity

accurate, widely available, rapid testing that effectively enables specific activities

continued advancements in therapeutics (including pre- and postexposure prophylactics) for and clinical management of COVID-19, leading to lower infection-fatality ratios—substantial progress has already been made through a combination of effective drugs, such as dexamethasone and remdesivir, and changes in clinical management

public confidence that there aren’t significant long-term health consequences for those who recover from COVID-19

Both the epidemiological and normalcy ends to the COVID-19 pandemic are important. The transition to the next normal will mark an important social and economic milestone, and herd immunity will be a more definitive end to the pandemic. In the United States, while the transition to normal might be accomplished sooner, the epidemiological end point looks most likely to be reached in the second half of 2021. Other advanced economies are probably on similar timetables.

Indian Strategic Studies

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1 May 2021

When will the COVID-19 pandemic end?

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