Why Covid is surging this summer — and what health experts say has changed

President Biden’s recent positive test for Covid-19 is a sign of a broader trend: Covid cases are on the rise this summer, gauged by rising wastewater measures and an increase in hospitalizations.

Many Americans have likely experienced the uptick firsthand over the past few weeks. They’ve either tested positive themselves or know someone else chagrined to see those two lines bloom on a home test. Even as SARS-CoV-2 has joined the ranks of the respiratory viruses that will continue circulating and causing infections, a spike in cases like this summer’s still causes disruptions in people’s lives — as well as some confusion over issues like tracking down tests, the best time to get vaccine boosters, and the latest advice on managing the infection.

STAT spoke with experts in infectious disease, virology, and public health to find out what people need to know about this summer’s Covid surge. One key message: Despite the increase in cases, the protection people have built up thanks to rounds of vaccination and prior infections is still sparing the vast majority of people from severe illness.

“Once you really get a decent immunity, you may get the virus again, but you’re probably not going to get very sick from it,” said Aaron Glatt, chair and professor of medicine at Mount Sinai South Nassau.

The latest data on Covid cases in the U.S.

It’s not clear just how many people are contracting SARS-2 at any given point, both because of a lack of testing and because so many infections are likely so mild that people don’t even think to test. But metrics like wastewater data and hospitalizations do show some increased Covid activity in recent weeks.

The latest CDC wastewater numbers rate viral activity as “high” in July, though still far below a steeper uptick in January of this year that is in turn dwarfed by a giant peak in January 2022, when Omicron first ruled.

This summertime surge — “surge” is relative, compared to past spikes of the virus — is, in many ways, entirely predictable. While experts debate just how far along SARS-2 is in its anticipated journey to seasonality, it has reared its head to varying extents each of the five summers it’s been around, going back to 2020 (though which month it’s peaked has varied over the years).

The rate at which infections result in hospitalizations or deaths, however, has fallen dramatically, thanks to all the immunity people have accrued.

Overall, weekly Covid deaths are at their lowest point since the virus emerged more than four years ago.

The virus, like other pathogens that most people shake off, can still occasionally cause severe cases. It is also still killing a few hundred people each week, the vast majority of whom are older and likely have other health conditions, which is why it’s so crucial for people in those groups to keep up with boosters and to be treated for their infections. For the week ended July 20, 229 deaths were attributed to Covid, per the most recent data reported to the CDC, compared to 540 deaths during the same period in the previous year and 3,226 for the same period in July 2022.

The virus is also still causing new cases of long Covid, though vaccination has lowered the risk of developing the condition.

Glatt calls hospitalizations a surrogate for what’s happening in the community. Over the last month or so, admissions at the New York hospital have gone from only two or three patients with Covid to 10 to 15.

“I think people have to understand that we’re probably going to be dealing with Covid for many, many, many years to come. There will be waxing and waning of infections, summer or winter,” said Glatt, who is also a spokesperson for the Infectious Diseases Society of America.

Why Covid cases are rising this summer

Why, you might wonder, is Covid still causing so many infections in the summer, particularly when other respiratory viruses — like influenza, RSV, and the other endemic coronaviruses that cause colds — are generally constrained to the fall and winter?

There are a few reasons.

First off, the virus has evolved to be an incredibly adept spreader, particularly with the emergence of the Omicron variant.

It’s also that people become susceptible to an infection again not all that long after their most recent infection or booster shot. (Protection against severe outcomes holds up over time for most people.) This is a result of two factors: both the fact that immunity to SARS-2 infections naturally wanes over weeks and months, and that the virus continues to evolve in ways that allow it to infect people even who have several layers of protection. People who have extremely mild cases might also not mount much of an immune response, so their body won’t have a strong shield up for the next time they’re exposed to the virus.

These twice-a-year spikes in cases have led some experts to argue that, if the virus isn’t limited largely to the colder months, it is still showing periodicity. That is, it can cause a wave of cases roughly every six months or so, likely as a result of enough people becoming susceptible to infection again.

What are the latest Covid variants?

The continued evolution of this coronavirus is not unique — it’s just what viruses do. Yet in part because of the way different SARS-2 variants have so drastically altered the course of the pandemic (think of the Delta and the original Omicron variants back in 2021), there is still increased attention on how the virus is evolving.

Since Omicron emerged, different branches of the variant have risen in dominance and then fallen as something else emerged. Currently, a trio of substrains — called KP.3, KP.2, and LB.1 — are on the upswing. Even with the ongoing mutating of the virus, nothing that’s emerged in the past two years has changed the Covid landscape all that dramatically, particularly compared to the variants that arose in 2021.

How long do Covid tests last?

Amid the rise in cases, free at-home test kits are no longer available. The Biden administration resumed its offering of free tests in September of last year, but the program shut down in March. Another federal program that offered free Covid testing — Home Test to Treat — launched in March 2022 but was phased out at the end of May.

“It’s definitely a difficult position that it might put a lot of Americans in,” Michael Mina, co-director of the Home Test to Treat program and chief scientific officer at eMed, said of the lack of free at-home tests. “When they’re getting them for free, they’re really happy to test and use those tests, but not when they’re paying 20 bucks a box for them.”

Mina said any difficulty Americans may encounter in accessing Covid tests at their local pharmacies may be simply due to the lack of demand. “It’s a market feature, and CVS and Walgreens know what the demand looks like.”

Those who do have trouble finding new at-home tests to purchase may wonder if they can use older kits they have stashed away. The FDA says that tests generally shouldn’t be used beyond their expiration date, though it notes that expiration dates can be extended when test manufacturers submit “stability testing” results showing that their kits have a longer shelf life. The FDA keeps a database of authorized over-the-counter Covid tests with their most updated expiration dates.

The evolving guidance on what to do if you have Covid

An ongoing public-health challenge is that it’s hard to know who’s infectious with Covid at what point in time.

“One of the biggest holes we still have in knowledge is I can’t tell you if somebody is contagious,” Glatt said. “We usually go by symptoms and some duration of time from their onset of symptoms. But that’s a very poor guide to the real likelihood that somebody is contagious or not to someone else.”

CDC guidelines say people should isolate for five days from their first Covid symptoms, after which they can be around other people if they’ve been fever-free for 24 hours and wear masks inside.

Jonathan Li, an infectious disease doctor and an associate professor of medicine at Harvard Medical School and Brigham and Women’s Hospital, said the CDC is trying to be practical with its advice, moving toward treating Covid like other respiratory viruses such as flu and RSV. The recommendation for other respiratory viruses is to isolate until you’re fever-free for 24 hours and your symptoms have improved.

“There is supporting evidence that because immunity is now generally widespread, the risk of infection for someone who has a healthy immune system is now relatively low,” he said. “The main problem, of course, remains our immunocompromised patients. Those are the individuals still at high risk that we really still need to learn more about and to optimize their treatments.”

There is a new treatment for people whose immunity is impaired by disease or transplantation, a monoclonal antibody called pemivibart (sold as Pemgarda), but it’s expensive and given by infusion. It provides a similar level of protection as vaccines do to everyone else — for now. Its efficacy can be lost as the virus changes but appears to be effective against the current circulating variants.

The latest advice on when to get Covid booster shots

Vaccines and boosters are the go-to protections against the virus. But is it better to get boosters now or later, after they’ve been updated to fight more recent variants?

“For those who are at highest risk — the very elderly, the elderly with comorbidities, and also immunocompromised — I would say go ahead and get one now. The vaccines now still are active against some of the circulating variants,” Li said. “By the time the new vaccine comes out in a few months or so, you’ll be eligible to get another shot toward the late fall.”

For those whose risks are a bit lower, Li said, waiting until the fall boosters come out would also be reasonable.

As for the latest CDC guidance, an advisory panel in February recommended spring boosters for people 65 and older who’d had their last dose at least four months before. That four-month interval would also be the gap before receiving the newer, updated vaccine in the fall. CDC suggests waiting three months after an infection before getting another dose in order to improve immune response.

“If you’re 50 years old with some mild underlying heart disease and you haven’t had a booster in a year, maybe you want to wait till the fall when they come out with new vaccines,” Mount Sinai’s Glatt said. “There’s no right and there’s no wrong answer. It’s how much risk somebody’s willing to take.”

What about ‘novids’?

You’ve heard about people who, to their knowledge, have never been infected with Covid-19. You may also have heard they’re acquiring their first infections this summer. What gives?

Some people have really good immune responses. Some people just have really good luck. But their luck may have run out, along with protection from their boosters last fall or winter.

“They’re at a little bit more risk,” Brigham’s Li said. “Plus the fact that the circulating variants are immune evasive, so a little bit harder to neutralize by our current immune responses. If I had to guess, I would say that this group of individuals who have never had Covid is going to continue to shrink over time.”

And that leaves us where?

In the end, Covid-19 is less seasonal because it’s more transmissible than other respiratory viruses like flu for which we get our shots in the fall. And it’s not going away.

“The fact is it’s one of those viruses that’s going to be with us, I think, year-round. And I think we’re going to have to learn to live with it,” Li said. “We’re going to have to learn to manage it and to try to protect those amongst us who are the most vulnerable.”