Last week, the U.S. Food and Drug Administration added seniors and people with high-COVID-19-risk jobs to the list of people approved for a third dose of the Pfizer vaccine.
A new CDC report evaluates how third doses affected their predecessors: people with conditions that compromise their immune systems.
Using health check-in surveys from its v-safe phone app, the CDC gathered data from more than 12,000 of the roughly 2.2 million people in the U.S. who had received third doses as of Sept. 19.
Nearly all received their third shot from the same manufacturer as their first.
Reported symptoms included fatigue, headache and pain at the injection site. The generally mild symptoms lasted less than a week and happened about as often as they did with second doses.
Around one-third of respondents said they couldn't perform normal daily activities, usually on the day after vaccination. Less than 2% sought medical care.
The CDC will continue monitoring vaccine safety.
