When U.S. sprinter Noah Lyles was upset in a race this month at the Paris Olympics, weakened by COVID-19 and earning only a bronze medal, the coronavirus that once stopped the world made headlines again. But the coverage also underscored that SARS-CoV-2 has become yesterday’s news—barely more interesting than the flu or the common cold unless it affects sports, a politician, or a celebrity.
Still, the big summer surge of COVID-19 that hit Lyles is also a reminder that the disease has not yet lost its ability to cause major outbreaks—and kill thousands—despite increased population-wide immunity from repeated vaccinations and infections. “Over and over again this virus has proven that it’s very clever at evolving to infect large numbers of people,” says Shane Crotty, a virologist at the La Jolla Institute for Immunology.
Gauging the scope of this summer’s outbreak is difficult because most countries have stopped routine reporting of cases. However, wastewater testing for SARS-CoV-2 genes still offers an indicator. Data collected by the U.S. Centers for Disease Control and Prevention show that in the United States, virus levels on 10 August were at their highest point since 13 January and still climbing. Other countries reported similar summer spikes in waste-water. In the United Kingdom, the percentage of polymerase chain reaction tests that came back positive for SARS-CoV-2 peaked on 14 July at a level last seen in October 2023.
What’s causing this summer wave, and what does it portend? Science asked COVID-19 researchers these and other pressing questions.
Why is COVID-19 surging now?
The two main factors in the ebb and flow of SARS-CoV-2 are the emergence of new viral variants that escape immune responses, and waning immunity from previous exposure to the virus and vaccines. It’s “really hard” to disentangle the two, says Sam Scarpino, a computational biologist at Northeastern University who specializes in analyzing complex systems. But studies suggest waning immunity is less of a problem than the virus’ shapeshifting abilities.
The SARS-CoV-2 variants circulating today are all members of a strain called Omicron, first identified by South African researchers in November 2021. The virus has evolved a great deal since then, most notably with the emergence in August 2023 of BA.2.86 and its descendant JN.1. Those lineages differ from previously circulating Omicron strains by more than 30 mutations in the viral surface protein known as spike, allowing the variants to “escape” existing immunity. “It clearly no longer makes sense to call them Omicron because they’re so different,” says Kristian Andersen, an evolutionary biologist at Scripps Research.
Research shows most people in the U.S. still have strong antibody and T cell responses against SARS-CoV-2, though they many not be strong enough to prevent illness or slow spread.
For example, a study in the 11 July issue of Nature Communications showed that among some 55,000 people in New York City whose blood has been tested since the start of the pandemic, more than 90% by 2022 had antibodies to the virus, which persisted at moderate to high levels through the last sampling of participants in October 2023. But JN.1 and subsequent variants have broken through that immunity, says Viviana Simon, a virologist at the Icahn School of Medicine at Mount Sinai and lead author of the paper.
Is human behavior driving this surge?
We don’t really know. Some scientists have speculated brutal heat waves and humidity in Europe and the U.S. make people spend more time indoors—with the air conditioning on—where the virus spreads far better than outside. That memories of the pandemic have receded clearly plays a role as well, says University of Oxford epidemiologist Christopher Dye. The public has “no appetite” for any restrictions that would slow transmission, he says, and few people still wear masks. “Many people are not particularly bothered about getting it, and they’re not bothering to test,” Dye says.
Are severe disease and deaths from COVID-19 declining?
Yes—they have been for several years. In the U.S., COVID-19 deaths peaked at nearly 26,000 a week in January 2021, the month a wide rollout of COVID-19 vaccines began. U.S. hospitalizations reached a peak 1 year later at 35.4 per 100,000 people, after the highly transmissible Omicron had burst onto the scene, causing record numbers of infections. During the current surge, the U.S. is seeing about 600 deaths a week, and only four people per 100,000 are hospitalized each week. Similar trends have occurred globally.
“We’re much better off now than a few years ago. But obviously, where we all want to be is to not get sick anymore, and so this summer has been disappointing,” Crotty says. COVID-19 “can be quite a nasty disease still,” Dye adds. “And then there’s the question of Long Covid, which people are still not thinking hard enough about.”
Do COVID-19 booster shots still make sense?
In June, the U.S. Food and Drug Administration advised vaccine-makers to manufacture boosters based on JN.1 and, “if feasible,” its descendant KP.2, which is now circulating widely. The shots should be available next month. But newer strains will likely circulate this fall, and Ira Longini, a biostatisican at the Univeristy of Florida, says people should not expect the boosters to protect them from infection—though he believes they will reduce the risk of severe disease for people who haven’t had COVID-19 or been boosted recently. “If you’re frail or worried you have an underlying condition, or you’re old, the booster makes sense,” Longini says. Roskilde University epidemiologist Lone Simonsen agrees, but is circumspect about boosting in younger, healthy people. “There’s so little severe disease that I don’t see the point in going and getting this vaccine every year,” she says.
Andersen, however, advocates a booster for anyone who hasn’t had a vaccine or an infection in 6 months. “I do think that people are looking at this a little too casually,” he says. “This is not a benign virus. Even if you don’t end up dying, it’s not great being sick and infecting others, and the potential effects of Long Covid are real.”
Are vaccines that provide better protection on the horizon?
There’s wide agreement that we need them. “We’re making vaccines against the variants that are going to be gone in 3 months by the time the vaccines are out, without much of a clue of where the virus is headed,” Scarpino says. “And so we’re going to be in this loop basically forever.”
A new generation of vaccines might offer a better way out. A company named Codagenix is just completing a phase 3 study of a novel vaccine that contains a live, weakened version of SARS-CoV-2. Squirted into the nose, the hope is the vaccine will create mucosal immunity at the portal of entry. “That’s the only potential game changer I see on the horizon,” Longini says.
Other researchers are hoping to develop COVID-19 vaccines that protect even against variants that have yet to emerge by combining pieces of related but widely divergent coronaviruses, including SARS-CoV-1 and viruses found in bats and pangolins. “This is the kind of research we really need to quickly invest heavily in,” says Michael Osterholm, an epidemiologist at the University of Minnesota School of Public Health, whose group published a road map to develop COVID-19 vaccines that trigger broader immune responses. “If we had different vaccines, we could do a lot more.”
Will COVID-19 become a seasonal disease, like flu?
Several infectious diseases wax and wane with the seasons, and many scientists expect that COVID-19 will eventually fall into a winter pattern, like influenza and some other viral respiratory diseases. So far, that hasn’t happened. “People keep asking about whether this is a seasonal virus, and my answer is: Yes, the seasonal virus that occurs in every season,” Osterholm jokes.
Still, Andersen sees a biseasonal pattern emerging in the U.S. and Europe. COVID-19 cases are now concentrated in winter and summer waves, and the latter seems to have started later this year than in 2023. The start of the next winter season “will probably be pushing into November, early December,” Andersen says. “Maybe next year there will be 7 months between waves, and then it will be 8 months and so on.” If that pattern continues, the summer wave will eventually disappear.
But disease seasonality is a poorly understood phenomenon. Micaela Martinez, an infectious disease ecologist at WE ACT for Environmental Justice, says the interplay between human immunity and SARS-CoV-2 evolution is still very dynamic. “You have new variants popping up over a certain time frame, which then could lock into a seasonality,” she says. But she has no idea whether that will occur in 10 years or 100 years from now. “That remains to be seen.”
