LEILA FADEL, HOST:

Millions of Americans are now eligible for booster shots. On Friday, the U.S. Food and Drug Administration authorized a third dose of the Pfizer and Moderna vaccines for adults over 18, with the Centers for Disease Control and Prevention quickly backing that authorization. And Dr. Anthony Fauci says this expansion could bode well for the U.S. come spring 2022.

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ANTHONY FAUCI: If we implement a good vaccination of the unvaccinated and a really good uptake of boosting those who are fully vaccinated by the spring, we can have a pretty good control of this.

FADEL: Joining us now is Dr. Peter Chin-Hong. He's an infectious disease specialist and professor at the University of California, San Francisco. Welcome to the program.

PETER CHIN-HONG: Thanks for having me on, Leila.

FADEL: So, Dr. Chin-Hong, Dr. Fauci seems optimistic about the potential outcome of a successful vaccination and booster shot campaign, saying that the U.S. can reach a point where COVID is not eliminated but endemic. So what does that mean, exactly?

CHIN-HONG: It means that we are accepting a certain level of disease in society, just like influenza, chickenpox. Sure, it will take some people to the hospital. Maybe we will have good medications for them. But we are not living in fear. We're not rushing and checking every statistic and metric, and we're not opening and closing down society but continuing life as we know it.

FADEL: What do we know about the protection booster shots offer?

CHIN-HONG: Well, we have some really good data now, actually. There's a well-conducted, randomized controlled trial by Pfizer of about 10,000 people, and it shows that the booster shot is about 95% effective. Whether or not you look at age, if you look at gender, race, ethnicity - it all looks effective across a wide swath of the population.

FADEL: Do all adults actually need the booster? Do the extra shots really benefit those under 65 who've already been vaccinated?

CHIN-HONG: Well, Leila, it depends on what your goalpost is. I think for the most part, as an infectious disease doctor, prevention of severe disease hospitalization and death is probably my golden apple. But around the time of Thanksgiving, holiday travel, being a health care worker - maybe prevention of infection is just as important. As a health care worker, you know, at - my institution at UCSF, for example has been encouraging boosters, even in younger individuals, because one health care worker taken off of the workforce during this vulnerable time will mean a lot to the institution. So it's really important to protect us not just against severe disease, which two shots do well, but also against infection.

FADEL: So will we need to get boosters regularly? And if so, how often?

CHIN-HONG: That's a great question. Well, many people think that we probably won't actually need a revolving door or sliding door every six months because something about giving that third shot several months after the last one reminds the immune system in a way that makes it mature and able to remember for much longer. Look at other vaccines - measles, mumps and rubella, hepatitis B, human papillomavirus - we have this one-two-punch, several months and then a boost. And we're kind of set for many years.

FADEL: So we should note that this authorization comes after some states, including your state, rolled out their own booster shot campaigns for adults. Why did it take the federal government longer to issue its approval?

CHIN-HONG: Well, one would say that the federal government actually acted in lightning speed with the FDA, so it was just that the states like California were looking - they were looking at the storm coming over from Europe. And given that California and other states had such a terrible winter last year, we didn't know when the FDA would give that final approval. We wanted to be proactive, and I think that's really what happened.

FADEL: Speaking of that, some experts are warning of a winter surge as families gather for the holidays. And the U.S. is experiencing another rise in cases right now. Would getting a booster shot sooner than later help to mitigate this?

CHIN-HONG: Totally. I mean, I think coming back to your earlier question about who really needs it - if you really want to preserve hospital resources, the group that I'm most worried about is those who are older than 65 and immunocompromised. So far, that group is only - only about 30% of them have gotten boosters, and more than 70% have received their first two shots more than six months ago. So I'm particularly worried about that group. Other than that, I think it would be an annoying infection for most. They'll be taken out of work, and I think that might mean a lot to some people, but it won't look like the same winter as last year as a country.

FADEL: And in the 30 seconds we have left - should there be so much focus on booster shots when so many people around the world haven't even received their first dose?

CHIN-HONG: That's such a great question, Leila. I think the answer is yes and yes. The booster shots come from a, you know - the pantry they already have allocated to the U.S. We need to continue to be proactive like the Biden administration is with investing many more dollars into the rest of the world. And until then, we can't control the pandemic.

FADEL: Dr. Peter Chin-Hong, thank you so much for joining us.

CHIN-HONG: Thank you. Transcript provided by NPR, Copyright NPR.