A fourth dose of the Pfizer/BioNTech Covid-19 vaccine seems to offer short-lived protection against infection overall, but protection against severe illness did not wane for at least several weeks, according to a new study.
The study, published Tuesday in the New England Journal of Medicine, looked at the health records of more than 1.25 million vaccinated people in Israel who were 60 or older from January through March 2022, a time when the Omicron coronavirus variant was the dominant strain.
The rate of severe Covid-19 infection in the fourth week after a fourth dose of vaccine was lower than in people who got only three doses by a factor of 3.5.
However, protection against severe illness did not seem to wane in the six weeks after the fourth shot, though the study period wasn’t long enough to determine exactly how long this protection lasts.
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