In documents posted online, the FDA took note of conflicting data concerning boosters.
The FDA said in a briefing document, “Some observational studies have suggested declining efficacy of COMIRNATY over time against symptomatic infection or against the Delta variant, while others have not.”
Data submitted to the FDA by Pfizer break down side effects experienced after the boosters. Pfizer asked its trial participants to submits their symptoms using an electronic diary.
The company said injection site pain was the most common side effect.
Pfizer said most side effects lasted up to two days.
It said severe side effects were rarely reported but when they were, it was severe fatigue and muscle pain. Trial participants ages 18 to 55 were the most likely to report any side effects.
|SYMPTOM||18-55 YEAR OLDS||65-85 YEAR OLDS|
|Injection site pain||83%||66.7%|
Other side effects felt less frequently were chills and new/worsened joint pain.
Several studies supporting boosters have been conducted in Israel, something the FDA also took note of saying US-based studies “may most accurately represent vaccine effectiveness in the US population.”
The FDA said data available to them showed the vaccines were still effective in preventing severe illness.