COVID rates in the U.S. have risen for the fourth summer in a row, elevating hospitalization rates and adding more weight to the argument that the virus has found summer seasonality, in addition to winter.
Nationally, COVID wastewater levels are similar to that of every pandemic summer except for 2022, when the world saw a spike due to Omicron variant BA.5.
The U.S. Center for Disease Control and Prevention’s data tracker shows a 10.3% rise in hospitalizations July 9-15, the most recent period for which data is available. Deaths, however, are holding steady.
COVID wastewater levels are on the rise in the Houston area, and positive tests in the community have been elevated since late June, Dr. Michael Chang, pediatric infectious disease specialist at Children’s Memorial Hermann Hospital and UTHealth, tells Fortune.
But so far, that hasn’t translated into a significant increase in kids admitted to his hospital for COVID, he said. Still, “our colleagues in the city have reported some increased pediatric hospitalizations.” And his system’s adult hospitals have seen an increase in COVID hospitalizations since the end of June.
Cases are trending steadily upward in the southern region of the U.S., of which Texas is a part, according to BioBot Analytics, which monitors COVID wastewater levels for the federal government. They’re also trending steadily upward in the Northeast, and more sharply upward in the West and Midwest, though levels in both still lag the rest of the country.
Reasons behind the rise in COVID cases
Chang attributes this summer’s elevated level of COVID cases to increased indoor activities driven by heat and people seeking air conditioning. Similarly, winter spikes are attributable to increased indoor activities driven by cold and people seeking heat. Summer travel is likely also contributing, he said.
Another factor: Waning immunity. Antibody immunity from both infection and vaccination lasts roughly three to six months. Those who were infected last winter are likely more susceptible to the virus again.
While new XBB.1.5 COVID boosters are expected this fall, the variant is “on its way out,” Raj Rajnarayanan—assistant dean of research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark., and a top COVID-variant tracker—told Fortune.
“By the time the booster hits the market, there won’t be any XBB.1.5 in circulation,” he said, referencing the strain known as “Kraken” that grew rapidly last winter. It comprised an estimated 12% of U.S. cases last week.
The new jabs should still be useful, Rajnarayanan said, as the XBB.1.5 variant holds a good deal of similarities to top variants in circulation now.
But it’s hard to say how the booster will hold up to the new variants the world is seeing by the time it rolls out, he added.
Like other respiratory viruses, COVID seems to spike in the winter. As for whether the virus will become a summer trend we can count on, Chang said he doesn’t think we can definitively draw that conclusion—yet.
While properties of the virus can influence seasonality, so can the behavior of humans. For instance, people abandoning COVID mitigation strategies like masking and distancing caused a rise in cases in and of itself, viral properties aside.
But people’s COVID-related behavior, or lack thereof, “has stabilized in the last two summers,” Chang said.
“This summer will give us the best answer to whether we see summer spikes every year, depending on how big this summer wave turns out to be.”