Just over 22,000 of the first Americans in line for a third dose, many of them immunocompromised, shared information about their side effects after their third shot through their smartphones, as part of the CDC's v-safe vaccine safety surveillance system.
They reported the side effects after the third dose were similar to those commonly experienced after the second dose.
Of the 22, 191 participants who received a third shot, 71% reported injection site pain, 56% had fatigue and 43% experienced headache.
CDC Director Rochelle Walensky says researchers have not seen any unusual patterns in this first group to receive the third dose.
"The frequency and type of side effects were similar to those seen after the second vaccine doses and were mostly mild or moderate and short-lived," Walensky says.
Localized reactions were slightly less common after the third dose, but systemic, or full-body, reactions were slightly more common.
Of the v-safe participants who received a third shot, 32% reported the side effects impacted their health and 28% say they were unable to perform normal daily activities, most commonly on the day after their injection.
Boosters of the Pfizer-BioNTech are now recommended for people 65 and older, adults with underlying health conditions like obesity, diabetes, or high blood pressure, and those who work or live in higher-risk settings.
Health officials recommend waiting 6 months after your second dose of the Pfizer vaccine before receiving a booster shot.
"If you are eligible for a vaccine booster and you have questions, I encourage you to go to vaccines.gov, talk with your healthcare provider, pharmacist or a health professional about your current risk for COVID-19, the benefit of a vaccine booster dose and the safety of receiving of an additional dose," Dr. Walensky says.
About 55% of Americans are now fully vaccinated.
About 70 million of those eligible for the COVID-19 vaccines remain unvaccinated.