4th Pfizer dose slashes risk of catching omicron in study
Bloomberg August 2, 2022
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Hospital workers who got a fourth dose of Pfizer's messenger RNA vaccine were far less likely to get COVID than triple-vaccinated peers in a study.
The findings published Tuesday in the American Medical Association's open access journal are the latest to confirm the benefits of a second booster against breakthrough infections caused by omicron. The study's authors pointed to an extra dose as a tool to prevent medical staff shortages and spare health systems in times of strain.
The research was conducted in Israel, where a speedy vaccine roll-out has provided scientists with real-world data on vaccine efficacy. The country started offering a second booster to the elderly, health workers and those with weakened immune systems in January.
The U.S. is now considering whether to expand eligibility for second booster shots amid the spread of the BA.5 omicron variant.
Doctors, nurses and other health-care workers who got a fourth mRNA shot in January showed a 7% rate of breakthrough infections. Those with three doses — the third having been administered by the end of September — saw an infection rate of 20%.
Many health workers in Israel opted not to get a fourth dose in January, the scientists said, assuming it wouldn't make much of a difference.
"The common assumption was that the combination of reduced virulence of the omicron variant and the protection given by the first three vaccine doses created no added value for the fourth vaccine," they wrote. But for medical staff, they argued such a difference matters because "quarantine and isolation of a large number of health-care workers may impair the ability of the health system to function."