Scientists are beginning to come up with answers to the question of how long antibodies from an infection can protect you — and what they'll protect you from.

Transcript

STEVE INSKEEP, BYLINE: We're moving into the third year of the pandemic, and a lot of people have now had COVID-19. In fact, scientists estimate the vast majority of Americans have been infected at some point. By the end of this month, it might be 80% of us at one time or another who have been infected. So here's a question. If most of us have been infected or vaccinated, or vaccinated and infected, can we just return to normal now? Well, maybe not.

But we've been asking NPR global health correspondent Michaeleen Doucleff to figure out what this does mean.

Hey there, Michaeleen.

MICHAELEEN DOUCLEFF, BYLINE: Hi, Steve.

INSKEEP: Where does that 80% figure come from?

DOUCLEFF: You know, it's hard to know exactly the percentage because many COVID cases go undetected.

INSKEEP: Sure.

DOUCLEFF: And as we'll learn, there can be reinfections. But roughly, researchers at Georgia Tech estimate that before omicron, about 40% of Americans had been infected. And researchers at the University of Washington predict about 40% of Americans will catch omicron.

INSKEEP: So 40% plus 40% - that's 80%. That's most of us. Does that mean that most people, whether they're vaccinated or not, have some protection from the disease?

DOUCLEFF: Yes. So they are protected in a particular way. So what scientists are beginning to realize is having a symptomatic infection typically triggers a strong immune response and gives good protection against severe disease in future surges.

Laith Abu-Raddad has been researching this topic for over a year. He's an epidemiologist at Weill Cornell Medicine - Qatar. And in a recent study, he measured a person's risk of getting hospitalized during their second infection compared to their first.

LAITH ABU-RADDAD: Those who get reinfected had 90% lower chance of getting hospitalized than those who had a primary infection.

DOUCLEFF: And he says there's growing evidence that this protection lasts quite a long time - perhaps a few years.

INSKEEP: Wow. So you have a tiny fraction of the odds of going to the hospital with a serious illness if you catch it again.

DOUCLEFF: Yes. It's quite extraordinary. And it means that over time, COVID will be less of a problem for society as a whole.

ABU-RADDAD: That would be really good news because then it will allow us to live with the pandemic in a much easier way.

DOUCLEFF: Now, Abu-Raddad is quick to point out that this long-term protection is seen with healthy people under age 50 and is likely less for people who are older or who have underlying health conditions.

INSKEEP: I'm glad you're giving us some exceptions because I want to sort this out. There have been, throughout the pandemic, some people who've suggested if they just get COVID once, well, now they're immune. And scientists and doctors have pushed back and said it doesn't actually provide you that much protection. Are doctors now saying it does provide you a lot of protection?

DOUCLEFF: So early on, the thinking, you know, that it didn't provide much protection was based on very preliminary data, which hasn't actually panned out. In fact, having COVID for healthy people may actually offer better protection than the vaccine against future variants. A recent study from the Centers for Disease Control and Prevention found that a prior infection offered nearly three times the protection against hospitalization during the delta surge than two shots of the vaccine did. But having both - being vaccinated and having had an infection - gives the best protection.

INSKEEP: Does that mean that somebody who really locked down and wore the N95 mask and followed all the rules and did not get infected - that minority that's never been infected - are they even at a disadvantage now?

DOUCLEFF: No, no, no. People should still be taking precautions. Remember, even though cases are dropping here, more than 2,000 Americans are dying each day. That's more than 10 times the death rate seen with the flu.

INSKEEP: Is that the reason that you would still not say to people, go ahead and get this disease and get it over with?

DOUCLEFF: Yeah, absolutely. This is still a very scary disease. There's no guarantee your first infection is going to be mild, so you don't want to deliberately get infected.

INSKEEP: But if you're one of the people for whom this is out of their hands because they've already been infected, and maybe they've been vaccinated and infected, does that mean they won't get COVID again?

DOUCLEFF: You know, that was the hope - right? - that once we're all vaccinated and had a bout of COVID, we wouldn't catch COVID again.

But Jeffrey Townsend at Yale University says, with this virus, that's not going to happen.

JEFFREY TOWNSEND: Yes, reinfections are possible. In fact, they're pretty much inevitable. At least all the evidence that we have now says that's true.

DOUCLEFF: Some of that evidence comes from Townsend and his colleagues studying the other coronaviruses, which are related to SARS-CoV-2 but are different. These viruses cause the common cold.

TOWNSEND: They all infect and reinfect on a, you know, several-year timescale. And there's no reason to expect something different from this virus.

DOUCLEFF: He says the risk of reinfection is very low for about three to six months right after you're sick. But then the risk grows, and many people will be reinfected every year or two.

INSKEEP: So your immunity wanes. But you do have that three- to six-month period right after you've been infected. Can you take fewer precautions then?

DOUCLEFF: You know, that is the period when you are best protected, especially if you're vaccinated. But, of course, your risk depends on your personal situation, like whether you have kids in school or you're exposed often at work. And it also depends on the virus - how much it changes. During the delta surge, a previous infection offered about 85% protection against reinfection. But with omicron, that protection dropped down to 55%. So the chance of reinfection was much higher. So that will likely happen again with a future variant.

INSKEEP: Michaeleen, can you talk us through one other thing? It's been hard for me to get my brain around this. I would have thought a vaccine was to prevent me from getting the disease. It turns out that if my immune system is boosted in some way, I might be good at preventing severe disease, but I might still be infected. How could that be?

DOUCLEFF: Yeah. And it's what many scientists are talking about right now. And some believe this is a deliberate decision by the immune system.

Jonathan Yewdell is an immunologist at the National Institutes of Health, and he spoke about this on the podcast "This Week In Virology." He says that your immune system has decided that with coronaviruses, it's not worth stopping the infection, as long as it can stop serious illness.

JONATHAN YEWDELL: You know, you might not think when you're in bed with 106 fever, you know, and crying for your spouse to help you 'cause you could barely move that this is good enough. But as long as you recovered from that, then the immune system would say, you know, mission accomplished.

DOUCLEFF: He says, you know, the immune system is built to keep us alive, not stop every sickness or asymptomatic infection or give us a negative PCR test. So, Steve, the future of COVID is a lot more infections, but hopefully a lot fewer hospitalizations and deaths.

INSKEEP: NPR's Michaeleen Doucleff - always a pleasure - thanks.

DOUCLEFF: Thank you, Steve.

(SOUNDBITE OF KATASHI KAITO'S "SAD EMOJI") Transcript provided by NPR, Copyright NPR.

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