A U.S. study has shown that most of the side effects observed following a third dose of a COVID vaccine are mild or moderate, and occur as often as after the second dose. 

The Centers for Disease Control and Prevention’s report came from over 22,000 individuals who signed up to a vaccine safety app and were administered a booster dose from August 12 through September 19, when the boosters were authorized for the immunocompromised, and not for the wider population.CDC director Rochelle Walensky said that the frequency and type of side effects following the booster shot were found to be similar to those observed following the second dose. The side effects were mild or moderate. Commonly reported side effects were injection site pain (71%), fatigue (56%), and headache (43%)… (NDTV – AFP, September 29, 2021)