When will the Covid-19 pandemic end?

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Europe and the United States have entered the endemic stage of the Covid-19 outbreak: the virus is widespread, is significantly less fatal than it was in 2020, and is spurring only limited changes in public behaviour. These endemic conditions are likely to continue through the summer and autumn, unless and until immunity-evading new variants emerge. As immunity wanes, however, the next stage remains highly uncertain. In this update, we discuss the outlook, the current and potential future use of boosters and therapeutics, and the shifts in response strategies to the Covid-19 crisis around the world.

The past few months have seen many parts of the world, including Europe and North America, continue their journey toward endemic Covid-19. While the BA.5 subvariant has produced a rise in the number of cases in many places, the burden of severe disease remains low in Europe and is only moderately higher in the United States, thanks to the lower average severity of Omicron subvariants and high levels of partial immunity. Countries such as Australia and New Zealand have decreased their previously strong focus on controlling viral spread and are now transitioning to strategies for managing endemic disease. They have seen continued success, recording higher case counts but few deaths. The experience of these countries, with total excess mortality from the pandemic far lower than it is in other parts of the world and only a limited need for ongoing restrictions, can make a case that their response to the Covid-19 pandemic has been among the most effective in the world.

As of mid-July 2022, mainland China is the only large country pursuing a zero-Covid-19 strategy. That approach has kept the number of deaths caused by Covid-19 low. Nonetheless, the relatively low levels of immunity among the population, including the elderly, make the endgame for this approach less clear than it is for countries that have shifted away from a zero-Covid-19 strategy. In the meantime, the current approach appears to have had substantial and mostly negative effects on both the Chinese and the global economies.

Looking ahead, the outlook for most regions, including Europe and North America, remains relatively favourable for the coming months, with levels of severe disease at or below recent levels. The winter of 2022–23 may see a more substantial uptick in the Northern Hemisphere, but this is unlikely to be as severe as the December 2021–February 2022 wave. Two caveats are important. First, the term relatively favourable needs qualification. While many people in the United States are growing comfortable living alongside Covid-19, the average number of daily deaths still runs at two to four times the long-term average for influenza, and it’s higher on a seasonally adjusted basis. Second, a new, immunity-evading variant could upend this relatively optimistic story at any time. Delta-cron (Omicron’s twin) and Milder-cron scenarios we described in our March 2022 update remain a reasonable summary of the range of possibilities for the impact of future variants.

Subvariants of Omicron, especially BA.5, have challenged the world with ever more transmissible versions of the virus. But so far, they haven’t fundamentally changed the dynamics of the pandemic, because there hasn’t been a step change decline in immunity, as seen during the winter, when Omicron first emerged. To be sure, some tentative evidence that BA.4 and BA.5 can evade immunity is emerging. For the moment, however, scientists view these variants as simply more transmissible than Omicron. The vaccines now in wide distribution still limit the incidence of severe disease.

Vaccines, therapeutics, and tests

Although advances in detecting and treating Covid-19 lead the news less frequently than they did a year ago, important developments continue to emerge. Public-health authorities around the world are considering short- and medium-term strategies for the timing and rollout of booster shots. Many are already recommending fourth doses for those at highest risk of severe disease, given recent studies highlighting the additional benefit provided. Some are debating a strategy that would combine annual flu and Covid-19 boosters in the autumn.

However, the future uptake of boosters is a significant unknown. In the United States, only about half of those who received the initial course of Covid-19 vaccines have received the first booster. It isn’t yet clear whether public interest in boosters will continue to decline or demand will in time match the historical uptake of flu vaccines (around 50 percent of adults). Without continued immunization, population immunity to current variants, including Omicron, will lessen over time. But Omicron-specific boosters (especially to address BA.4 and BA.5) could potentially emerge this autumn and significantly enhance the efficacy of vaccines against the predominant strain.

The recent authorization of Covid-19 vaccines for children as young as six months is also an important step. Of course, the low rate of severe Covid-19 in this age group means that the impact on paediatric mortality will be small. But there is hope that vaccinating young children will increase overall population immunity (a critical metric, as we discuss later in the article).

Paxlovid and other Covid-19 therapeutics are now widely available in high-income countries. In the United States, supply is well ahead of demand. Increasing the uptake of effective therapeutics is an important step for governments as they continue the transition toward managing endemic Covid-19. These therapeutics, including both small-molecule and antibody treatments, have helped blunt the incidence of severe disease in places where they are widely available. But the same shortfalls in access that bedevil the distribution of vaccines in low-income countries are striking again with therapeutics: doses sit unused in high-income countries while other parts of the world lack access.

Testing for Covid-19 has increasingly shifted to a home-based model. Since so few results from home tests are reported, it has been difficult to estimate the current wave’s true magnitude in the United States. The official statistics, which already tend to underestimate the number of cases, may become even less sensitive to the true dimensions of viral transmission.

Public-health authorities may therefore need to look at a wider range of indicators to support their planning and disease management efforts. One such indicator may be consumer behaviour. Since home tests became more widely available, in late 2021, consumer purchases of them have risen in line with waves of Covid-19 cases, prefiguring rises in deaths attributable to the disease (Exhibit 1). It’s too soon to tell if rising numbers of test purchases reflect consumers’ awareness of symptomatic disease (when family members fall ill, for example), their knowledge of the spread of cases in the community, or other factors. But it seems likely that purchases of tests (like online searches of “flu near me”) are an indicator and could provide some advance warning of future waves of the disease. Over the past couple of months, the number of tests bought from one online retailer has been rising, which may reinforce the impression that the United States is entering a period of sustained case growth.

Estimating community risk

The risk that Covid-19 poses to a community at any point in time is a function of the immunity of its members. Immunity protects individuals and reduces risk for people in the community around them by reducing rates of onward transmission. It is gained through vaccination (primary series and boosters), infection with SARS-CoV-2, or both (hybrid immunity). It is lost both gradually, with the passage of time, and suddenly, when a new variant that evades the immunity afforded by vaccination or previous infection becomes dominant (as happened with the emergence of Omicron in late 2021). A community’s level of immunity is a precarious balance, constantly shifting as individuals gain and lose immunity.

Although each individual’s level of immunity cannot be measured in real time, we can base estimates of the level of community risk on what is known about vaccination rates and previous infections. Exhibit 2 summarizes that knowledge, based on the published literature and values derived from it. Note that the values shown define ranges of immune protection against symptomatic infection, since that is the metric most of the published literature uses. Protection against any infection (including asymptomatic disease) is likely to be lower—and protection against severe disease is likely to be higher. Ranges reflect the uncertainty around immunity levels and describe population averages. They are not intended to be predictive for any individual.

This information, combined with estimates of when infections and vaccinations took place, enables us to create the McKinsey Covid-19 Immunity Index, showing fluctuations in degrees of protection over time (see sidebar, “Description of methods for the McKinsey Covid-19 Immunity Index”). Exhibit 3 includes three types of immunity for six countries: immunity derived from previous infection only, from vaccination only, and from both (now the largest group in many countries). Higher scores mean that more people have immunity and that the community has greater protection against symptomatic disease.

Two communities might have the same score but different combinations of vaccination and prior infection. They might also have different outlooks for the next few months if their collective immunities are waning quickly or slowly. Note that immunity against symptomatic disease (not any disease) is what we try to assess; we don’t estimate a community’s threshold for herd immunity, as that would be driven by both symptomatic and asymptomatic infections.

This initial version of the McKinsey Covid-19 Immunity Index helps us make a few observations:

• The emergence of Omicron during the winter of 2021–22 is visible as a sharp drop in immunity in multiple countries (since existing immunity was suddenly less effective against the new variant).
• The proportion of unvaccinated people with past infections in a country is roughly correlated with its overall Covid-19 mortality, since unvaccinated but infected people have been at greatest risk of bad outcomes.
• Even countries, such as Italy and the United Kingdom, with strong vaccination track records may be starting to lose immunity as the pace of booster uptake drops over the summer (although most countries are prioritizing boosters for the highest risk populations).
• As Australia transitions its Covid-19 strategy, it has rapidly gained immunity over the past year through a combination of vaccination and infections.
• Vaccination remains an essential element in building immunity. Some new studies suggest that infection confers more immunity and protection against severe disease than does vaccination alone. As a result, some countries with strong vaccination records may now have lower immunity than others, such as the United States, that have experienced a large number of cases during recent Omicron waves and for which much of the population was last immunized about six months ago.
• Even countries, such as the United States, with high McKinsey Covid-19 Immunity Index scores continue to experience many new Covid-19 cases as a result of the extremely high transmissibility of current SARS-CoV-2 variants. US mortality for Covid-19 is still higher than the historical average for flu but has fallen by 85% to 90% since its early 2021 peak.
• A successful autumn booster campaign in Northern Hemisphere countries will be important to increasing immunity levels before winter comes.

One significant limitation of the McKinsey Covid-19 Immunity Index is that it doesn’t indicate which people within a community are protected. A country in which the elderly are overwhelmingly immune will have much better outcomes than will a similar country where the same level of overall immunity is concentrated in the young. Immunity can only partly predict the burden of disease at any point in time. Other important drivers of disease trends include the variant mix, the season, and behaviour (such as masking, compliance with isolation and quarantines, and working from home). However, the McKinsey Covid-19 Immunity Index can be helpful in understanding a society’s level of protection. Measurements like it can help inform both individual behaviour and public policy during the next chapter of the Covid-19 pandemic.