The world is worried about the Delta virus variant. Studies show vaccines are effective against it.

By Carl Zimmer
July 6, 2021

As the Delta variant sweeps the world, researchers are tracking how well vaccines protect against it — and getting different answers.

In Britain, researchers reported in May that two doses of the Pfizer-BioNTech vaccine had an effectiveness of 88 percent protecting against symptomatic disease from Delta. A June study from Scotland concluded the vaccine was 79 percent effective against the variant. On Saturday, a team of researchers in Canada pegged its effectiveness at 87 percent.

And on Monday, Israel’s Ministry of Health announced that the effectiveness of the Pfizer-BioNTech vaccine was 64 percent against all coronavirus infections, down from about 95 percent in May, before the Delta variant began its climb to near-total dominance in Israel.

Although the range of these numbers may seem confusing, vaccine experts say it should be expected because it’s hard for a single study to accurately pinpoint the effectiveness of a vaccine.

“We just have to take everything together as little pieces of a puzzle, and not put too much weight on any one number,” said Natalie Dean, a biostatistician at Emory University.

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