June 2021. The world has been in pandemic mode for a year and a half. The virus continues to spread at a slow burn; intermittent lockdowns are the new normal. An approved vaccine offers six months of protection, but international deal-making has slowed its distribution. An estimated 250 million people have been infected worldwide, and 1.75 million are dead.
Scenarios such as this one imagine how the COVID-19 pandemic might play out1. Around the world, epidemiologists are constructing short- and long-term projections as a way to prepare for, and potentially mitigate, the spread and impact of SARS-CoV-2, the virus that causes COVID-19. Although their forecasts and timelines vary, modellers agree on two things: COVID-19 is here to stay, and the future depends on a lot of unknowns, including whether people develop lasting immunity to the virus, whether seasonality affects its spread, and — perhaps most importantly — the choices made by governments and individuals. “A lot of places are unlocking, and a lot of places aren’t. We don’t really yet know what’s going to happen,” says Rosalind Eggo, an infectious-disease modeller at the London School of Hygiene & Tropical Medicine (LSHTM).
“The future will very much depend on how much social mixing resumes, and what kind of prevention we do,” says Joseph Wu, a disease modeller at the University of Hong Kong. Recent models and evidence from successful lockdowns suggest that behavioural changes can reduce the spread of COVID-19 if most, but not necessarily all, people comply.
Last week, the number of confirmed COVID-19 infections passed 15 million globally, with around 650,000 deaths. Lockdowns are easing in many countries, leading some people to assume that the pandemic is ending, says Yonatan Grad, an epidemiologist at the Harvard T. H. Chan School of Public Health in Boston, Massachusetts. “But that’s not the case. We’re in for a long haul.”
If immunity to the virus lasts less than a year, for example, similar to other human coronaviruses in circulation, there could be annual surges in COVID-19 infections through to 2025 and beyond. Here, Nature explores what the science says about the months and years to come.
The pandemic is not playing out in the same way from place to place. Countries such as China, New Zealand and Rwanda have reached a low level of cases — after lockdowns of varying lengths — and are easing restrictions while watching for flare-ups. Elsewhere, such as in the United States and Brazil, cases are rising fast after governments lifted lockdowns quickly or never activated them nationwide.
The latter group has modellers very worried. In South Africa, which now ranks fifth in the world for total COVID-19 cases, a consortium of modellers estimates2 that the country can expect a peak in August or September, with around one million active cases, and cumulatively as many as 13 million symptomatic cases by early November. In terms of hospital resources, “we’re already breaching capacity in some areas, so I think our best-case scenario is not a good one”, says Juliet Pulliam, director of the South African Centre for Epidemiological Modelling and Analysis at Stellenbosch University.