***This article is published as a preprint.***
ABSTRACT
The ongoing Omicron wave of the COVID-19 pandemic has resulted in unprecedented levels of population transmission due to the variant’s high level of infectiousness. We have seen repeatedly that the epidemiological characteristics of new variants can have profound impacts on global health outcomes, and while the characteristics of these new variants are difficult to predict ahead of their emergence, considering the impact of potential future scenarios is of critical importance for planning and policy making. This paper samples across a range of potential variant-level characteristics to provide global forecasts of infections, hospitalisations, and deaths in the face of high (but waning) levels of past immunity, and evaluates a range of interventions that may diminish the impact of future waves.
Methods
We created a susceptible-exposed-infectious dynamic model that accounts for vaccine uptake and effectiveness, new variants, and waning protection from both infection- and vaccine-derived immunity. Using this model, we first estimated past infections, hospitalisations, and deaths by variant, location, and day. We used these findings to more fully understand the global progression of the COVID-19 pandemic through May 31, 2022. Second, we forecasted these same outcome measures for five different scenarios based on future emergence of variants, and then four sub-scenarios within each potential variant scenario, to evaluate the impact of available intervention strategies through November 30, 2022.
Findings
We estimated that from November 15, 2021, through May 31, 2022, there were 3.83 billion (95% uncertainty interval [UI] 2.99–4.67) SARS-CoV-2 infections, 10.4 million (8.26–13.4) hospitalisations, and 2.44 million (2.06–2.89) deaths, the majority of which were attributable to the Omicron variant (96.3% (92.5-97.6) of infections, 74.7% (59.7-82.3) of hospitalisations, and 61.9% (46.9-67.8) of deaths). Compared to the pre-Omicron pandemic period from January 1, 2020, to November 14, 2021, we estimated that there were approximately the same number of infections globally from November 15, 2021, to May 31, 2022, but only 23.6% (18.0-25.9) of the estimated deaths. The massive Omicron wave and relatively high vaccination rates in many high-income countries have together contributed to high levels of partial or full immunity against SARS-CoV-2 infection, leaving only 4.48% (3.15–6.21) of the global population with no protection as of May 31, 2022. Under the future scenario we consider most plausible (a scenario with a new Omicron-like variant emerging and reference levels of the drivers of transmission), we estimated there will be an additional 3.45 billion (1.67–5.34) infections, 3.57 million (1.69–6.33) hospitalisations, and 816,000 (367,000–1,420,000) deaths between June 1, 2022, and November 30, 2022, with the Americas and European WHO regions projected to sustain the highest rates of additional deaths. If we consider a variant that combines the high infectiousness of Omicron with the high severity of Delta, we again estimate 3.45 billion (1.67–5.34) new infections, but due to the presumed increase in severe outcomes, we estimate 4.62 million (1.47– 8.61) deaths over the forecasted period. We estimate that resumed mask usage (to 80% of the population in each location, or the current level, whichever is higher) would, on average, reduce the number of deaths by at least 50% across all the potential variant futures we considered, while a delayed but eventual global scale-up of antivirals would reduce deaths, on average, by at least 20% across variant scenarios.
Interpretation
As infection-derived and conferred protection wanes, we expect infections to rise, but given the large proportion of the population that had some level of immunity to SARS-CoV-2 as of June 1, 2022, all but the most pessimistic forecasts in this analysis do not predict a massive global surge by November 30, 2022. All signs point towards COVID-19 transitioning into a more endemic transmission regime (lower, but sustained disease burden), and with the introduction and proliferation of novel therapeutic interventions expected in mid- to late 2022, the likelihood of returning to past levels of COVID-19 mortality is low. The characteristics of future COVID-19 variants are difficult to predict, and our forecasts do show some considerable variation in outcomes as a function of variant properties. Given the uncertainty surrounding what type of variant will next emerge, we must remain vigilant as we move to the next phase of the COVID-19 pandemic. Despite the very important role of vaccines and the potential role of new therapeutics, the contribution of mask usage to the prevention of infection and death cannot be understated. Masks are a simple and effective COVID-19 reduction strategy that—under a scenario in which an Omicron-like variant emerges on approximately June 1, 2022—could prevent about 433,000 deaths (223,000–712,130) between June 1 and November 30, 2022, if worn universally. Under our worst-case variant scenario, high mask use could prevent an estimated 2.33 million (0.836–4.08) deaths.
Note: Funding: Bill & Melinda Gates Foundation, J. Stanton, T. Gillespie, and J. and E. Nordstrom.
Declaration of Interest: None.
