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COVID-19 Vaccines Vs. COVID-19 Variants

ARI SHAPIRO, HOST:

It's official. U.S. health authorities say the mutant strain of coronavirus that was first identified in the U.K. last winter is now also the predominant strain in the U.S. On a reassuring note, officials say there is strong evidence that all three of the vaccines approved for use in the U.S. offer good protection against this variant. But this strain is actually just one of three so-called variants of concern. So how well do vaccines work against the other two? NPR's Nurith Aizenman reports.

NURITH AIZENMAN, BYLINE: All three variants of concern have been found in the U.S., as well as in a broad swath of other countries. And across the world, there are 10 vaccines in play. So this question - how well does each of the vaccines work against each of the worrying mutant strains? - it's one of the hottest topics in biomedical research right now.

SALIM ABDOOL KARIM: We have seen an explosion, a paper almost every day.

AIZENMAN: Salim Abdool Karim is an infectious disease researcher who co-chairs the COVID Advisory Committee for South Africa, where the second variant of concern was initially spotted. Abdool Karim says, in order to judge which vaccines make most sense for his country, ideally he wants to know how the vaccine is performing against South Africa's variant in real-world conditions.

ABDOOL KARIM: And we've been quite fortunate that we've had several of the vaccines that have been tested in South Africa.

AIZENMAN: For instance, a large study of Johnson & Johnson's vaccine found it was about 85% effective at preventing severe disease from the variant dominant in South Africa. A smaller study of the Pfizer vaccine suggests it prevents as much as 100% of even mild cases from the variant in South Africa. But on the less hopeful side, a study of the Novavax vaccine suggests that while it's about 89% effective at preventing mild disease from the original strain, it's only about 50% as effective against the variant dominant in South Africa.

ABDOOL KARIM: Almost half the efficacy is lost.

AIZENMAN: Worse still, a study of the AstraZeneca vaccine suggests it may have almost no ability to prevent mild disease from the variant in South Africa, though it's unclear how well either AstraZeneca or Novavax prevent serious illness. Then there are six other vaccines for which there are no clinical studies to go by. To assess those, Abdool Karim is looking to laboratory studies. Scientists take blood from a vaccinated person and extract the antibodies that the vaccine generated against the virus. Then they put those antibodies in a petri dish with one of the mutant strains of the virus.

ABDOOL KARIM: They look at, you know, how much of antibody is required to kill the virus.

AIZENMAN: Several such experiments with the Moderna vaccine suggest that because the antibodies it generates are not as effective against the variant in South Africa, it takes eight times as many of them to knock out that strain. But Abdool Karim says he's not too worried.

ABDOOL KARIM: The Moderna vaccine produces pretty high levels of antibodies, and so there is enough antibodies still to neutralize the virus.

AIZENMAN: By contrast, an experiment found that for AstraZeneca, it takes 86 times as many antibodies to neutralize the variant in South Africa compared to the original strain. While there's no hard-and-fast rule, Abdool Karim says, when it gets to that point...

ABDOOL KARIM: I don't - then I'm basically not confident about the vaccine at all.

AIZENMAN: If the variant first found in South Africa has generated the most consternation among scientists, a close second is a variant that's prevalent in Brazil. Kate O'Brien is director of the World Health Organization's Department of Immunization, Vaccines and Biologicals. She says the issue for that variant is not so much the studies so far, which are actually not all that alarming, but that there are still too few of them on this variant.

KATE O'BRIEN: There's just not enough information, really, to draw any substantive conclusions.

AIZENMAN: O'Brien says all this means it's likely officials may end up adjusting their advice on which vaccines should be used where. If that happens, she says...

O'BRIEN: I think the public needs to understand that it's not because policymakers got it wrong the first time.

AIZENMAN: It's because new evidence has come in.

Nurith Aizenman, NPR News.

(SOUNDBITE OF L'IMPERATRICE'S "SONATE PACIFIQUE") Transcript provided by NPR, Copyright NPR.