Fever after 4th shot milder than after 3rd

The Yomiuri Shimbun

17:01 JST, October 9, 2022

One in four people develop a fever of 37.5 C or higher following a fourth shot of Pfizer Inc.’s coronavirus vaccine, according to an interim report by a team from Juntendo University and other institutions.

However, the frequency of major side effects tends to be lower compared with those following a third inoculation. The team reported their findings Friday to an expert panel of the Health, Labor and Welfare Ministry.

Of 1,490 health care workers and others who received a fourth Pfizer shot, 26% registered a fever of 37.5 C or higher within a week, while 14% had a fever of 38 C or higher.

The interim report says 40% of people logged a fever of 37.5 C or higher after a third shot of the vaccine, while 21% saw the mercury rise to 38 C or higher. The percentage of people who developed a fever tended to be lower following the fourth inoculation.

The team also examined the effects of a fourth dose of the vaccine made by U.S. firm Moderna Inc. Of 690 patients, 39% had a fever of 37.5 C or higher, while 22% experienced temperatures of 38 C or more.

As with the Pfizer product, the percentage of those who developed a fever tended to be lower after a third shot of the Moderna vaccine.