Side effects and safety information
| In the arm where you got the shot: | Throughout the rest of your body: |
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These side effects usually start within a day or two of getting the vaccine. They might feel like flu symptoms and might even affect your ability to do daily activities, but they should go away in a few days. Get tips on what to expect after getting vaccinated.
Summary of safety data
- In clinical trials, reactogenicity symptoms (side effects that happen within 7 days of getting vaccinated) were common but were mostly mild to moderate.
- Side effects (such as fever, chills, tiredness, and headache) throughout the body were more common after the second dose of the vaccine.
- Most side effects were mild to moderate. However, a small number of people had severe side effects—defined as side effects affecting a person’s ability to do daily activities.
- Although few people in the clinical trials went to the hospital or died, data suggest that people who got the Pfizer-BioNTech vaccine were less likely to have these more serious outcomes compared to people who got the saline placebo.
- CDC will continue to provide updates as we learn more about the safety of the Pfizer-BioNTech vaccine in real-world conditions. Learn more about vaccine safety monitoring after a vaccine is authorized or approved for use.
Learn more about safety and reactogenicity data from the clinical trials.
Information on how well the vaccine works
- Based on evidence from clinical trials, the Pfizer-BioNTech vaccine was 95% effective at preventing laboratory-confirmed COVID-19 illness in people without evidence of previous infection.
- CDC will continue to provide updates as we learn more about how well the Pfizer-BioNTech vaccine works in real-world conditions.
Demographic information from clinical trials
Phase 2 and 3 clinical trials for the Pfizer-BioNTech vaccine included people from the following racial and ethnic categories:
- 81.9% White
- 26.2% Hispanic/Latino
- 9.8% African American
- 4.4% Asian
- <3% other races/ethnicities
Age and sex breakdown:
- 50.6% male
- 49.4% female
- 21.4% 65 years and older
The most frequent underlying medical conditions were obesity (35.1%), diabetes (8.4%), and pulmonary disease (7.8%).
Learn more about demographic information for people who participated in the trials.external icon