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The Pfizer-BioNTech COVID-19 vaccine is extremely effective against two dangerous variants of the coronavirus, the B.1.1.7 strain first found in the United Kingdom and the B.1.351 variant discovered in South Africa, researchers reported Wednesday in the New England Journal of Medicine and The Lancet.

Moderna also reported Wednesday that, according to early results from its booster shot trial, a third dose of its vaccine given six to eight months after the first two doses boosted antibodies to protect against the South African B.1.351 variant and other worrisome strain found in Brazil. Moderna is testing its original vaccine and a version modified to target the B.1.351 variant.

The new variants are more transmissible than the original strain and, some studies suggest, deadlier. The New England Journal of Medicine study examined records of more than 200,000 people from Qatar's COVID-19 database. The Pfizer vaccine was 87 to 89.5 percent effective at preventing infection from the B.1.1.7 variant among people two weeks past their second shot, 72.1 to 75 percent effective against the B.1.351 variant, and 100 percent effective at preventing severe, critical, or fatal cases of either variant, the researchers found.

The study in The Lancet was based on more than 230,000 cases from Israel. It found that the Pfizer vaccine was more than 95 percent effective against infection, hospitalization, or death in fully vaccinated people 16 and older, and 94 percent effective in people 85 and older. The vaccine efficacy numbers aren't self-evident, but Brains On!, a science podcast for kids, has a short, entertaining, and pretty effective explanation using defecating seagulls. You can watch that below. Peter Weber