When will the COVID-19 pandemic end?

24.12.2021

Известие о новом штамме коронавируса спустя два года после начала пандемии, унесшей более пяти миллионов жизней, вынуждает людей со всего мира собрать энергию для новой главы в этой истории. Компания Mckinsey проанализировала сценарии дальнейшего развития пандемии и выявила три аспекта, которые будут влиять на ее скорейшее преодоление. Подробнее о том, когда может закончиться пандемия, читайте в материале

On November 26, 2021, WHO reached deeper into the Greek alphabet to declare Omicron a new SARS-CoV-2 variant of concern.1 The world’s reaction has been an unpleasant mixture of dread, fatigue, and déjà vu. Almost two years into a pandemic that has claimed more than five million lives and affected billions more, people everywhere are finding it hard to summon the energy for another chapter in the story.

Endemicity remains the endpoint. But at the time of writing, the Omicron variant is rewriting the timetable. Whether because Omicron is more infectious or has greater ability to evade the immune system, or both, it quickly became the dominant variant in South Africa. Data so far are mixed on the severity of the disease it causes: some early findings have pointed toward a mild clinical course, while other evidence has suggested that Omicron may lead to more frequent hospitalization in children than other variants do. We have written previously about the transition to managing COVID-19 as an endemic disease and noted that a new variant was one of the greatest risks to timelines.

This article presents a new analysis of a range of scenarios based on the infectiousness, immune evasion, and severity of disease caused by the Omicron variant. Based on the evidence to date, we have posited a base-case scenario in which Omicron is about 25 percent more infectious, evades prior immunity to a greater degree (25 percent), and causes less severe disease, again by about 25 percent, all relative to Delta. Our analysis suggests that in the United States, this combination of characteristics would lead to Omicron replacing Delta as the dominant variant in the next few months and to a higher peak burden of disease than the country saw in the second half of 2021 (but likely below the peak reached in the winter of 2020–21).

This base-case scenario has the potential to place a severe strain on healthcare systems. The optimistic scenario would see a peak of disease burden close to that seen over the past six months, while the pessimistic would see a very significantly higher burden of disease than in the past six months. Note that in every scenario, our analysis indicates that hospitalizations will likely be higher in the next six months than they were in the past six months.

In any scenario for the future of the COVID-19 pandemic, much depends on the ways in which societies respond. Three levers are likely to be especially important, starting with the extent to which countries can effectively scale and make available new oral therapeutics with the potential to reduce the chance of progression to severe disease, and which are unlikely to be blunted by Omicron. Second, evidence is accumulating that booster doses are especially important for protecting against the Omicron variant; accelerating their rollout will help protect populations. And third, given public fatigue and the lessons of the past two years, finding the right combination of public-health measures will be critical.

The Omicron variant

Three main factors determine the real-world impact of any new SARS-CoV-2 variant: the extent to which it can evade the immunity developed by those who have been vaccinated or previously infected by other variants, its inherent infectiousness (often expressed as a higher basic reproduction number, or R0), and the severity of disease caused. The first two factors combine to drive the number of cases, while the third determines the number of severe cases and deaths. For example, the Delta variant, which remains dominant in most of the world, was significantly more transmissible than previously circulating variants were, showed limited incremental evasion of immunity, and caused moderately more severe disease relative to other variants.

Early data paint a mixed picture of Omicron’s evasion of vaccine-induced immunity. The UK Health Security Agency recently summed up its view: “Early estimates of vaccine effectiveness (VE) against symptomatic infection find a significantly lower VE [against] Omicron infection compared to Delta infection. Nevertheless, a moderate to high [VE] of 70 to 75% is seen in the early period after a booster dose.”

There is still much more to learn—sample sizes in the new studies were small, antibody titers are an imperfect metric of immune protection, and major manufacturers are yet to release similar information. The response to Omicron may include both accelerating the rollout of booster doses of existing vaccines and developing new formulations better targeted to this variant. Companies have indicated that modified or new vaccines could be available in a few months, though the scale and global availability are unclear.

Regarding evasion of natural immunity, a preprint article from South Africa suggests a significantly higher chance of reinfection by Omicron relative to Delta or Beta. Both the pace of case growth and the rapidly increasing share of Omicron among samples sequenced suggest that, through a combination of greater infectiousness and immune evasion, Omicron is spreading very quickly. If the experience of South Africa were to be repeated elsewhere, we could see a continued rapid increase in the number of COVID-19 cases as Omicron is established.

The question of disease severity is more complicated. Several clinicians in South Africa have noted the apparently mild presentation of Omicron cases. Further, the European Centre for Disease Prevention and Control (ECDC) noted on December 12, 2021, that 776 cases were within its remit and “all cases for which there is available information on severity were either asymptomatic or mild. There have been no Omicron-related deaths reported thus far.” On the other hand, ECDC also notes that it is too early to draw definitive conclusions on disease severity. The United Kingdom reported its first Omicron-related death on December 13, 2021, and some reports from South Africa suggest a potentially higher rate of hospitalization among young children than seen in previous waves of COVID-19.

In the base-case scenario, US COVID-19-related hospitalizations could peak significantly higher in the next six months than in the past six months.

Each of these observed trends may change as sample sizes increase, confounding factors are considered, and the clinical course of disease plays out over time. The answers, when they arrive, will have important consequences for the months ahead. Given the uncertainty, we have built a set of scenarios describing potential outcomes measured by hospitalization rate. They are indexed on the recent Delta wave and show whether various potential combinations of infectiousness, immune evasion, and clinical severity are likely to lead to a higher or lower rate of COVID-19-related hospitalization.

The results of these scenarios for the United States are shown in Exhibit 1. Each of the three variables is an important driver of the outcomes. Evidence so far suggests that the Omicron variant, relative to Delta, is likely to be more infectious, show more immune evasion, and be less severe, on average. In the base case (25 percent more infectious; 25 percent greater immune evasion; 25 percent less severe disease), the COVID-19-related hospitalization rate in the United States could peak significantly higher in the next six months than in the past six. In the pessimistic scenarios, the peak number of hospitalizations for COVID-19 could be much higher in the next six months than in the past six months, whereas in the optimistic scenario, the number would be higher but similar to that seen in the second half of 2021, as waning immunity causes ongoing disease from a combination of the Delta and Omicron variants.

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