COVID-19 cases are rising in many states. What experts say makes this summer different.

Shortly before the start of the third summer of the pandemic, the USA is undergoing a sixth wave of COVID-19 cases.

Compared with previous surges, this one looks more like a swell, health experts said.

The rise in cases reported in the Northeast in recent weeks appears to have peaked, but upward trends continue in at least 21 states, according to a USA TODAY analysis of Johns Hopkins University data. Health experts said cases are likely higher because of underreported home tests.

Although cases are rising, health experts said hospitalizations remain in check. There are about 350 deaths reported per day based on a seven-day average, which is more than a hundred deaths less than this time last year, according to Johns Hopkins University data.

“We’re only about 10 to 15 cases higher than what we were a year ago as far as hospitalizations, and there are fewer patients requiring ICU care, which is encouraging,” said Dr. Adia Ross, chief medical officer of Duke Regional Hospital. “Even though cases are up, the hospitalizations are not as high as they have been.”

Here's what else is different going into the third pandemic summer:

Those who avoided COVID-19 are getting it for the first time

If it feels like everyone in your circle is getting sick, you’re not wrong.

COVID-19 is everywhere, and many who avoided the virus are getting it for the first time, said Dr. Stuart Ray, professor of medicine in the division of infectious diseases at Johns Hopkins University.

After more than two years of preventive measures, pandemic fatigue has set in, health experts said, and more people attend social gatherings and travel without wearing a mask.

“When you lower your guard at a time when the rates are high, you’re pretty likely to encounter someone who is positive,” Ray said.

Public health officials have warned of high case rates for months, but experts said people's behavior is partly responsible for driving cases higher.

“The reason why it doesn’t feel as urgent to people is because everyone knows someone who has had COVID or has had it themselves. And in people who are immunized, most cases are relatively mild,” said Dr. Paul Sax, professor of medicine at Harvard Medical School and clinical director of the division of infectious diseases at Brigham and Women’s Hospital.

For every person who has a mild case of COVID-19, somewhere in the chain of transmission is someone who may have developed severe disease.

“The problem is that there’s so much COVID out there that the people who are most vulnerable are still getting quite sick,” Sax said.

Most report mild disease, but not everyone is so lucky

Experts said average Americans can expect a mild bout of COVID-19 if they’re infected with the virus this summer, as most people are immunized through vaccination, previous infection or both.

Omicron has some of the same symptoms as previous coronavirus variants, such as fever and fatigue, but some distinctive COVID-19 symptoms are becoming less common, health experts said, including coughing and a loss of taste or smell.

Despite these anecdotal differences, Sax said, physicians should be on guard for the common signs of COVID-19.

“Symptoms (may) vary from variant to variant,” Sax said. “But these generalizations are not enough to make that much of a difference clinically.”

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Those who are unvaccinated are more likely to develop severe disease compared with the vaccinated, experts said. The majority of hospitalizations occur among the elderly, those who are immunocompromised or patients with underlying conditions, with a “smattering of people who are unvaccinated,” Ray said.

“We are no longer naïve to this virus, either because of vaccination or prior infection or both. The fact that we’ve seen it before makes the subsequent cases milder,” Sax said. “This is not the holy grail herd immunity, but it’s related to that, meaning the background immunity in the population is making the disease less severe.”

People already sick with omicron are getting it again

Although many people are at least partly immunized against the virus, reinfections occur regardless of vaccination status.

Data shows immunity from previous infection and from the vaccines wanes, experts said, so reinfections are expected. But they are surprised people are catching thesame variant again.

“Reinfections are not surprising,” said Dr. Cameron Wolfe, an associate professor at Duke University School of Medicine and infectious disease specialist at Duke Health. “What has been a little disappointing, to me at least, is we’re starting to see reinfections of people who had omicron getting omicron again.”

Previously, people were mostly susceptible to reinfection only from a new variant.

Though omicron has remained predominant since the beginning of the year, it has spawned sublineages, including BA.2, BA.2.12, and BA.2.12.1. Experts said these subvariants may be different enough to evade immunity from a previous infection, or the immunity derived from omicron may not be as protective as other variants.

“It seems immunity generated by omicron isn’t quite as strong as we would have hoped,” Wolfe said.

The basics remain the same

Despite the differences from previous pandemic summers, health experts said, the basics of COVID-19 haven’t changed.

They urge Americans to avoid infection because the long-term consequences of the disease are unknown. Researchers continue to study post-COVID-19 conditions, commonly known as long COVID.

“I don’t think we have enough time and experience to know the long-term effects of having had COVID,” Ray said. “I’m not interested in taking on an unknown risk.”

The Centers for Disease Control and Prevention said post-COVID-19 conditions can include a wide range of physical and neurological health problems, such as fatigue, difficulty breathing, joint pain and brain fog. The agency defines "long COVID" as symptoms persisting at least four weeks after infection.

Americans should get vaccinated and wear masks during periods of high transmission to protect those vulnerable to severe disease, experts said.

“There’s a significant proportion of the population that are immunocompromised, and it’s a serious virus to them,” Sax said. “What I’m advising people is that they understand the risks of what they’re doing and always remember the vulnerable.”

Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

This article originally appeared on USA TODAY: Another summer COVID wave? Experts explain what's new this time around