Information about the Pfizer-BioNTech COVID-19 Vaccine

Side effects and safety information

In the arm where you got the shot: Throughout the rest of your body:
Most common side effects
  • Chills
  • Tiredness
  • Headache


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

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