ARI SHAPIRO, HOST:
The omicron variant hit the U.S. and spread fast. The Centers for Disease Control and Prevention now says omicron causes about three-quarters of the new COVID cases in the country, and those numbers will rise quickly because omicron spreads much more quickly than previous variants. Scientists have also learned that two doses of an MRNA vaccine don't prevent infections against omicron; boosters are key, and timing is key.
To explain, we're joined by NPR global health correspondent Michaeleen Doucleff.
Hey there.
MICHAELEEN DOUCLEFF, BYLINE: Hi, Ari.
SHAPIRO: Why are boosters so much more important with the omicron variant than they seemed to be just a few months ago?
DOUCLEFF: So with two shots, you still get protection against severe disease, and that will help keep you out of the hospital. That protection is about 70%. But with the booster, your body starts to make antibodies that can better bind to and neutralize omicron. With only two shots, you might have very few of these antibodies.
I was talking to Wilfredo Garcia Beltran about this. He's an immunologist at the Massachusetts General Hospital. He has evidence from the lab showing that a booster shot may restore vaccine protection almost to the level we see with the delta variant.
WILFREDO GARCIA BELTRAN: We know what happened last year. It was horrible. It was like (imitating explosion). But you can imagine if everyone gets boosted, it's going to really help and stop this massive wildfire spread if you have a large portion of the population that's been boosted.
SHAPIRO: So let's talk about timing. Right now, adults are eligible for a booster two months after the J&J vaccine and six months after Moderna or Pfizer. Should that timeline be shortened, given what we know?
DOUCLEFF: Yeah. So if you've had J&J, definitely go get that booster right at the two-month mark. For those who have had the MRNA vaccines, six months is probably an ideal time to wait for a booster. But several countries, including Germany, are starting to shorten the time to three months.
I talked to Dr. Dan Barouch about this. He runs the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston. He says that given the situation with omicron, a shorter time might make sense for some people.
DAN BAROUCH: I would say that if somebody is in the second half of the six-month timeframe and if they really feel like they would benefit from a higher level of protection, then I don't see a downside in getting boosted a bit earlier than the six-month period.
SHAPIRO: But that is not the current recommendation.
DOUCLEFF: Yeah.
SHAPIRO: And so how easy is it for somebody to get a booster after four or five months in the U.S.?
DOUCLEFF: So talk to your doctor about it. And Barouch is quick to point out that you shouldn't boost too early. You need at least three months and as close to six months as possible.
SHAPIRO: What's the risk if you do it too early? Why not do it right away?
DOUCLEFF: Yeah. So right after you get your first two shots, the antibodies you make actually aren't great at neutralizing omicron. But over time, special immune cells called B cells train these antibodies so they get better at binding omicron. But this training takes time - at least three months.
So before you get a booster, you want to be sure your immune system has time to improve its antibodies so you make ones that can fight omicron. Otherwise, you'll just be boosting the ones that don't work very well.
SHAPIRO: You know, older people in the U.S. started getting booster shots a few months ago now. Is it possible that a few months from now, they're going to need another booster shot 'cause six months will have gone by?
DOUCLEFF: Yeah. So, you know, eventually, we're probably going to be in a situation similar to what we have now with the flu, where you get an update of the vaccine every year or so to stop infections. But protection against severe disease is likely to hold up for a long time with COVID given how well it's held up against omicron.
SHAPIRO: And finally, what about mixing and matching different kinds of vaccines?
DOUCLEFF: Yeah. So studies have shown that you're better off getting an MRNA vaccine, so Pfizer or Moderna, after the J&J vaccine, that mixing and matching with the J&J is really important. It can boost antibodies about 10 times more than just with getting another J&J shot. We expect more data soon on how well this combination performs against omicron.
SHAPIRO: NPR global health correspondent Michaeleen Doucleff, thank you so much.
DOUCLEFF: Thank you, Ari. Transcript provided by NPR, Copyright NPR.
