COVID-19 hospitalizations are creeping up in the U.S. for the first time this year as extreme heat keeps people indoors and protection against infection fades.

COVID hospital admissions rose 43% in the last week in July from a low in the week ending June 24, according to Centers for Disease Control and Prevention data.

While they’re still lower than at any other point over thee past three years, public health officials across the country are urging caution about increases.

As COVID-19 becomes more established, experts say occasional bumps in cases and hospital admissions will likely continue – though the virus’s future course isn’t set in stone. It still poses a threat to older people and those with compromised immune systems, they caution, and can cause lingering long COVID symptoms even among those without risk factors.

It’s not a “full-blown, terrifying global outbreak, but nor is it gone,” said Jesse Goodman, a professor of medicine at Georgetown University. “Nor is it something that, particularly for our most vulnerable people, we can let our guard down about.”

New vaccines will be available in the fall, targeted to strains currently in circulation, and experts said it’s important that vulnerable people get boosted. Still, access to shots has been reduced as the US has stopped purchasing them for the public from Pfizer Inc. and Moderna Inc.

The shots are still available through health care providers. At-risk people attending large gatherings should consider a repeat immunization with vaccines on the market, rather than wait for the next crop of boosters, said Thomas Russo, chief of the Division of Infectious Diseases at the University of Buffalo’s medical school.

Masks also remain an option, and vulnerable people with symptoms should get tested so they can receive antivirals like Pfizer’s Paxlovid that decrease the risk of hospitalization and death if they’re taken early in an infection, Russo said.

Summer spike

Cases and hospitalizations started to rise in New York City in the middle of last month, according to health department spokesperson Patrick Gallahue.

In the Austin, Texas, area, wastewater sampling shows viral levels increasing over the last six weeks, the city’s health department said, an important indicator of infection levels.

Sales of at-home COVID-19 tests, another signal of concern, rose 43% at Rite Aid Corp. stores over the past four weeks, compared to the prior four, spokesperson Catherine Carter said in an email. Drugstore chains CVS Health Corp. and Walgreens Boots Alliance Inc. also noted heightened demand for diagnostics.

In an unusual twist for a respiratory diseases, extreme heat – rather than cold – is likely fueling the uptick.

July was Earth’s hottest month on record, and heat continues to bake much of the U.S. this month.

As sweltering weather pushes activities and gatherings indoors, the virus has more opportunities to spread, Russo said. Meanwhile, people have taken off masks and started traveling again as cases have fallen. It’s been months since many had their last immunization, whether through vaccination or contracting the virus, so protection against infection is waning.

At the same time, vaccines and past waves have given many people lasting protection against the worst outcomes of an infection, and the now-dominant omicron variant appears to cause less-severe disease than those that came before. Antivirals also help blunt the severity of infections.

“We’ll probably continue to see some bumps in hospitalizations,” Russo said. “But I’m hoping it’s going to be more muted.”

The rate of hospital admissions is still low in every state, according to the CDC: Fewer than 10 people in every 100,000 are hospitalized with the virus each week. Deaths are at their lowest level since March 2020, according to provisional CDC data, though they tend to increase later than hospitalizations.

Future risks

Since the first wave of omicron cases subsided in early 2022, hospitalizations and deaths have fluctuated but haven’t come close to the same heights. Periodic bumps without widespread disruption are the “most likely scenario” going forward, Goodman said – but there’s a lot that remains uncertain.

For one thing, it’s not clear whether COVID-19 will keep gaining ground every summer. While this is the fourth year it’s done so, it’s also possible waning immunity and emerging variants have created the illusion of a pattern. Other endemic coronaviruses that cause the common cold peak only in the fall and winter, said David Weber, a professor of medicine at the University of North Carolina.

If immunity continues to build, Russo said, the virus could almost completely disappear outside of seasonal peaks. The opposite could also happen, if a new variant is able to cause more severe disease or spread more rapidly than the versions of the virus in circulation today.

For now, there are no signs that’s happening. While a new strain, EG.5, recently became the most common in the US, there’s no evidence it spreads more easily than those that came before, CDC spokesperson Kathleen Conley said in an email. Current treatments and vaccines should continue to be effective against it, she said.

The real risk is that people don’t seek out COVID vaccines, tests and treatment, said Michael Merson, interim chair of the Department of Global and Environmental Health at New York University.

“My biggest concern is whether people get too complacent,” he said.