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CNN  — 

Covid-19 was never just another cold. We knew it was going to stick around and keep changing to try to get the upper hand on our immune systems.

But we’ve changed, too. Our B cells and T cells, keepers of our immune memories, aren’t as blind to this virus as they were when we first encountered the novel coronavirus in 2020. The US Centers for Disease Control and Prevention has screened blood samples and estimates that 97% of people in the US have some immunity to Covid-19 through vaccination, infection or both.

Then there’s science: We have updated vaccines and good antivirals to lean on when cases start to rise. Masks still work. Rapid tests are in stores. We now know to filter the air and to ventilate our spaces.

Those strategies, plus our hard-won immunity, had helped bring our national numbers of infections, hospitalizations and deaths down to levels that felt almost forgettable.

Almost.

Now that Covid-19 infections have started to rise again, it feels like people all over the country are testing positive, and it’s hard to know how to react. The government has been dialing back its response since the end of the public health emergency in May. Good Covid-19 data is hard to come by and harder to interpret.

So if people are less likely to be hospitalized or die from a Covid-19 infection now, has the danger passed? Is there still reason to worry if you do catch the infection for a second, third or fourth time?

Experts say it’s less risky to catch Covid-19 than it used to be, but there are still good reasons not to treat it casually.

“At this point, the risk is lower because of our prior immunity, whether for severe outcomes or for long Covid,” said Dr. Megan Ranney, an emergency physician and dean of the Yale School of Public Health.

“Covid is still more dangerous than the flu, but its level of danger is becoming less,” she said, noting that we’re still very early in our human experience with the coronavirus, even four years in, and there are still things we don’t know.

“But for it to behave like other respiratory viruses in terms of seasonality and surges is entirely expected,” she added.

It would be “really weird” for Covid to disappear or for it not to cause illnesses, hospitalizations and deaths. “It is still a virus,” Ranney said.

But a somewhat predictable waxing and waning of infections doesn’t make Covid-19 something to turn our backs on.

Our immune systems are better at spotting danger

After more than three grueling years, nearly all Americans have some immunity against Covid-19.

That means our immune systems – as long as they’re healthy and working as they should – will remember most forms of the coronavirus when it next comes our way.

That process takes some time to get going, however. That lag may give the virus enough of a window to get a foothold in our nasal passages or lungs, and we get sick. We may feel crummy for a few days, but then our B cells and T cells get their antibody production up and running. Eventually, they shut the virus down, and we get better.

That’s what should happen. But for many, their immune system just doesn’t kick in as quickly or as vigorously as it should.

Immune function drops off naturally with age. About 1 in 4 Americans is over the age of 60, according to census data. Then there are certain medications and health conditions that suppress immune function. About 3% of the U.S. population – 7 million people – is severely immunocompromised, according to the National Institutes of Health. This is a group taking medications to protect organ transplants or who are getting powerful drugs for cancer treatment, for example.

Then there’s individual variability. Through genetic bad luck, some people may just be at higher risk of serious reactions to Covid-19 infections, and they probably wouldn’t know it.

Taken together, that’s a sizeable pool of people who benefit greatly from having antibodies at the ready to take on the coronavirus as fast as possible. Vaccines get those antibodies in place and ready to work as soon as they’re needed.

Sometimes, people are so immunocompromised that vaccines can’t help them much, either. They benefit from preventive shots containing Covid-fighting antibodies that are built to stick around the body for a few months. Until this year, there was such a preventive product available, Evusheld. But the virus has evolved so much that Evusheld lost its potency, and in January, the FDA revoked its authorization.

Since then, people who have very low immune function haven’t had anything to protect them from infection or severe disease. But that could change. The government announced this week that it’s funding the development of a new preventive antibody through the drug company Regeneron. Trials of that drug are expected to start this fall, accordi