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Emerging variants and waning immunity are likely to push infections higher in the northern hemisphere as influenza also makes a comeback. Evidence is building that the northern hemisphere is on course for a surge of COVID-19 cases this autumn and winter. New immune-evading strains of the SARS-CoV-2 Omicron variant, behaviour changes, and waning immunity mean that many countries could soon see large numbers of COVID infections — and potentially hospitalizations — say scientists. Nature explores the factors that might drive a COVID-19 wave — and what countries can do to blunt the effects with the new generation of vaccines that target Omicron.
Will there be a COVID-19 wave this autumn and winter?
In mid-August, an effort called the COVID-19 Scenario Modelling Hub laid out several possible US scenarios for the coming months. With surges caused by the BA.5 Omicron variant in the rear-view mirror — resulting in high population immunity — the United States could be in for a relatively quiet COVID-19 season, the models suggested, so long as vaccine booster campaigns began quickly and new variants didn’t emerge. Even with a new variant, a big surge in cases wasn’t certain. More than a month on, hospitalizations are declining in line with projections, says Justin Lessler, an infectious-disease epidemiologist at the University of North Carolina at Chapel Hill who leads the modelling effort. But other factors on the horizon could spell trouble. The rollout of new, ‘bivalent’ boosters “has been a little bit slow,” says Lessler. And there are now subtle signs that Omicron is evolving and spawning a new cast of immunity-dodging variants. “It could lead to some upswings as we go into the fall and winter months,” Lessler adds. Some US states are already beginning to see an uptick in cases, notes epidemiologist Jennifer Nuzzo at Brown University in Providence, Rhode Island. The United Kingdom’s weekly population survey of SARS-CoV-2 infections, a gold-standard in COVID data, has also documented an increase in COVID prevalence in its past two reports. Hospitalizations of people who test positive for SARS-CoV-2 are rising quickly — although from low levels — in Britain and other European countries. In the backdrop, a slew of immunity-dodging variants are emerging globally, and researchers think these variants will fuel an autumn–winter wave.
Are new variants behind rising case numbers?
Probably not yet, says Tom Wenseleers, an evolutionary biologist at the Catholic University of Leuven in Belgium. The current rise in SARS-CoV-2 infections is probably largely because of people’s waning immunity — which offers short-lived protection from infection — as well as increased mixing between people. In many countries including the United Kingdom, social dynamics are nearly back to pre-pandemic levels, say health officials. Factors that cause other respiratory viruses to thrive in cooler months — including extra time spent indoors — could also be at play....
