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Vaccine protection vs. omicron infection may drop to 30% but does cut severe disease

A woman is vaccinated against COVID-19 at a clinic in Johannesburg on Dec. 6. A new study from South Africa looks at the effectiveness of the Pfizer vaccine in preventing infection and severe disease.
Shiraaz Mohamed
A woman is vaccinated against COVID-19 at a clinic in Johannesburg on Dec. 6. A new study from South Africa looks at the effectiveness of the Pfizer vaccine in preventing infection and severe disease.

The new coronavirus variant, called omicron, was first identified in South Africa only about a month ago and is already spreading quickly in Europe and North America. It has an exceptionally high number of mutations, and those mutations appear to make it more transmissible than the delta variant.

Now scientists in South Africa have just released the first data looking at how well the vaccines will work against the omicron variant. And the news is mixed.

The study comes from researchers at South Africa's largest private health insurer, called Discovery Health, and the South African Medical Research Council. In the study, described at a press briefing on Tuesday, scientists analyzed data from 78,000 people likely infected with omicron. Nearly half of them had received two doses of the Pfizer vaccine.

The study focused on the Pfizer vaccine. The Moderna shot isn't available in South Africa. In general, though, the two vaccines have behaved quite similarly against new variants, with the Moderna vaccine slightly more effective.

In the population in the South African study, the Pfizer vaccine's effectiveness against infection dropped down to about 30% for the omicron variant, compared with about 80% against the variant before omicron, the scientists reported.

That means the Pfizer vaccine reduces a person's risk of getting infected by about 30% compared to somebody who's not immunized.

By comparison, in the delta surge that began this summer in the U.S., the mRNA vaccines — Pfizer and Moderna — had an effectiveness of about 60% to 70% against infection, several studies have found.

With 30% effectiveness, there will be very many breakthrough infections.

But this new study does offer really good news when it comes to vaccine protection against severe disease: That dropped a bit but not nearly as much as protection against infection.

The vaccine is still working well to keep people out of the hospital

The researchers found that two shots of the Pfizer vaccine still offered about 70% protection against hospital admission because of COVID-19 in the population examined in the study. That's a drop from 90% observed during the previous surge in South Africa when the delta variant dominated. But 70% indicates the vaccine is still working well to keep people out of the hospital.

"We are encouraged that the Pfizer-BioNTech vaccine continues to offer high levels of protection from severe COVID-19 illness," Discovery Health CEO Ryan Noach said in a press statement.

In addition, the data suggests that the protection seems to hold up in people with some risk factors such as diabetes and heart disease, as well as in older people.

But these findings come with a huge caveat.

In South Africa, many people have been exposed to the coronavirus. Some studies estimate that up to 90% of South Africans have been infected over the course of the pandemic. The study didn't take this into account.

Scientists are starting to think that for many people, getting infected is almost like an extra dose of the vaccine. The infection really helps the immune system learn how to fight off COVID-19 — similar to the way the vaccine does.

And several studies have shown that if you've had an infection and then get two doses of an mRNA vaccine, you are much better protected compared to somebody who had only the vaccine.

So for people who've had only two shots — and not a prior infection — the vaccine's effectiveness in helping fight off an infection could be lower than 30%.

That said, boosters could be beneficial. Although this new study from South Africa didn't look at the effect of a third shot on preventing infection or severe disease by the omicron variant, a recent study from Goethe University Frankfurt did suggest that the booster could help restore some of the vaccine's effectiveness, especially in the short term after receiving the third shot. Based on that data, scientists are saying that a third shot is the best way to ward off omicron and, for those with a breakthrough infection, of preventing severe disease.

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Michaeleen Doucleff, PhD, is a correspondent for NPR's Science Desk. For nearly a decade, she has been reporting for the radio and the web for NPR's global health outlet, Goats and Soda. Doucleff focuses on disease outbreaks, cross-cultural parenting, and women and children's health.
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