Study Shows Pfizer Booster Shot Lowered Coronavirus Infection Risk

A third shot of the Pfizer Inc.–BioNTech SE Covid vaccine provides added protection against the coronavirus during a delta outbreak, according to early data from Israel, where boosters began rolling out incrementally in mid-July.

People who received the supplemental dose had a 48% to 68% lower risk of infection a week to 13 days later, compared to those who got the standard two-dose regimen, a preliminary analysis of data from Maccabi Healthcare Services found. The protection increased with time, with a 70% to 84% reduced risk of testing positive two weeks to 20 days after getting a third shot.

The research, released Tuesday ahead of peer-review and publication, assessed the additional effectiveness of a booster shot against infection due to the delta variant, but not severe disease, according to the researchers led by Daniel M. Weinberger, an associate professor of epidemiology at the Yale School of Public Health in New Haven, Connecticut.

The findings indicate that the waning of vaccine-induced protection against SARS-CoV-2 infection may be counteracted in the short term by a third dose, the authors said. The U.S., U.K. and other countries have announced plans to administer a booster shot to counter the more-infectious delta variant as antibody levels wane in those who were vaccinated earlier in the pandemic.

“As more time elapses, it will be possible to evaluate the effects on more rare but severe outcomes, such as hospitalization and death,” the researchers said. Further monitoring is needed to determine how long immunity from the booster lasts, they added.

Israel, an early leader in Covid-19 inoculations, reported a record number of daily infections Monday, giving fresh impetus to the country’s vaccine booster drive.