The Pfizer and AstraZeneca COVID-19 vaccines are highly effective against the variant first found in India, but only if you get both doses, real-world data shows


A woman receiving a COVID-19 vaccine on March 1 at a vaccination site in Los Angeles. Al Seib / Los Angeles Times

The Pfizer-BioNTech and Oxford University-AstraZeneca coronavirus vaccines are highly effective against the variant first found in India, which is thought to have fueled record-breaking infection numbers in the country and overwhelmed its healthcare system, new real-world data indicates.

The UK study, from England's public-health authority, found that two doses of the Pfizer-BioNTech vaccine were 88% effective at preventing symptomatic COVID-19 caused by the variant, which is called B.1.617.2. Two doses of the Oxford-AstraZeneca vaccine were 60% effective, the study found.

The UK has reported more than 4,000 cases of the variant, which has now spread to 49 countries including the US, according to Global Initiative on Sharing Avian Influenza Data. B.1.1.7, a variant first identified in the UK, remains the most common variant both there and in the US.

One dose offered far less protection, the Public Health England study found. A single dose of either vaccine was 33% effective against COVID-19 with symptoms caused by B.1.617.2.

The study, which was posted as a preprint Saturday and is yet to be peer-reviewed by other experts, is the first in the world to indicate that vaccines offer protection against B.1.617.2, which has mutations that make it highly infectious and might also make it able to escape antibodies produced by vaccines.

For comparison, two doses of Pfizer's vaccine were 93% effective against symptomatic COVID-19 caused by B.1.1.7, and AstraZeneca's was 66% effective. After one dose, both vaccines were 50% effective against B.1.1.7, the data indicated.

UK Health Secretary Matt Hancock said Sunday in a press release that the findings were "groundbreaking" and showed the importance of getting a second dose to secure the "strongest possible protection" against coronavirus variants.

2nd shot of Pfizer and AstraZeneca boosted protection
The PHE study adds to a growing body of real-world evidence that one dose of COVID-19 vaccines provides some protection against the coronavirus and that protection is boosted by the second dose. PHE's most recent surveillance report, for example, said a single dose of either Pfizer's or AstraZeneca's vaccine was 55% to 70% effective, rising to between 85% and 90% after two doses.

Adam Kucharski, an associate professor at the London School of Hygiene and Tropical Medicine, said on Twitter on Sunday that "first and foremost" the study was "another reminder that second doses matter."

The amount of protection offered by the vaccines could be more than it seems from the figures, as the PHE researchers did not look at whether the vaccines protected against severe disease caused by variants. COVID-19 vaccines typically offer more protection against these outcomes.

The lower efficacy of AstraZeneca's vaccine after two doses, compared with Pfizer's, could be down to the fact that it was given mostly to older people, who tend to have weaker immune responses, the study's authors said.

Other data has indicated that AstraZeneca's vaccine can take longer than Pfizer's to reach maximum effectiveness after the second dose.

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