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How well does a COVID vaccine hold up against the omicron variant?

RACHEL MARTIN, HOST:

We are learning more this morning about the new coronavirus variant, omicron, which is spreading quickly in Europe and North America. It has an exceptionally high number of mutations in it, and it appears to be more transmissible than the delta variant. Scientists in South Africa are now releasing the first data looking at how well the vaccines will work against this variant. Here to tell us what they found, NPR's global health correspondent Michaeleen Doucleff. Hey, Michaeleen.

MICHAELEEN DOUCLEFF, BYLINE: Hi, Rachel.

MARTIN: What do we need to know?

DOUCLEFF: So the findings come from South Africa's largest private health insurer, called Discovery Health, and the South African Medical Research Council. And in the study, scientists analyzed data from about 78,000 people likely infected with omicron. Nearly half of those people had received two doses of the Pfizer vaccine. In this population, the vaccine's effectiveness against infection dropped to about 30% for omicron compared to about 80% against the previous variant.

MARTIN: Thirty percent doesn't sound very good, Michaeleen. That's pretty low, right?

DOUCLEFF: It is quite low. So by comparison, here in the U.S. during the delta surge, the mRNA vaccines had an effectiveness of about 60 to 70%. So at 30%, they're going to be many, many breakthrough infections. And just to emphasize here, this is for protection against infection.

MARTIN: Then what about for severe disease? How well does the vaccine protect against that?

DOUCLEFF: Yeah. So here's some really good news. In this study, protection against severe disease dropped a bit, but not as much. So the researchers found that two shots of the Pfizer vaccine still offered about 70% protection against severe disease in this population. So that's a drop from 90%, but it does indicate that the vaccine is still working really well to keep people out of the hospital. Also, this protection seems to hold up in people with some risk factors, such as diabetes, as well as in older people.

MARTIN: OK. So that's good news. But you said in this population - is there reason to believe the vaccine effectiveness will be different here in the U.S. than it is in South Africa?

DOUCLEFF: Yeah. So this new data comes with a big caveat. In South Africa, many, many people have been exposed to the virus. Some studies estimate that nearly 90% of people have been infected over the course of the pandemic. And the study didn't take this into account because here's the thing about prior infections - scientists know now that when you get COVID, it's almost like you get an extra dose of the vaccine. An infection can really help the immune system learn to fight off the virus, like the shot does. And several studies have shown that if you've had an infection and then get the vaccine, you are much better protected compared to somebody who has only had two shots of the vaccine.

MARTIN: So are you saying the effectiveness of the vaccine against omicron could be less here in the U.S. than it is in South Africa?

DOUCLEFF: Yeah. Unfortunately, that's right. For people who have only had two shots and not a prior infection, the vaccine might not work as well, especially when it comes to fighting off an infection. It could actually be lower than 30% here in the U.S.

MARTIN: Then what about boosters? Is there any evidence that they could help here?

DOUCLEFF: Yeah, so this new study didn't look at the effect of a third shot. South Africa hasn't had the opportunity to roll out boosters yet. However, another study from the laboratory did suggest that boosters could help restore some of the vaccine's effectiveness, at least over the course of a few months or so. So getting a third shot is really your best chance at warding off omicron and delta and preventing severe disease.

MARTIN: I happen to have my appointment for my booster today. So...

DOUCLEFF: That's great news, Rachel.

MARTIN: Michaeleen Doucleff, thank you so much for your reporting on this. We appreciate it.

DOUCLEFF: Thank you for having me. Transcript provided by NPR, Copyright NPR.