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University Library, University of Illinois at Urbana-Champaign

COVID-19 Vaccines

Information and evidence about COVID-19 vaccine efficacy and safety


Safety Data Summary

  • 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.

SOURCE: CDC - ttps:// (April 15, 2021)

Clinical Trial Demographic Information

Clinical trials for the Pfizer-BioNTech vaccine included people from the following racial and ethnic, age, and sex categories:

  • 81.9% White
  • 9.8% African American
  • 4.4% Asian
  • <3% other races/ethnicities
  • <1% Native Hawaiian or Other Pacific Islander
  • <1% American Indian or Alaska Native


  • 2% Not Hispanic or Latino
  • 2% Hispanic of Latino
  • <1% Not Reported

Age and sex breakdown:

  • 50.6% male
  • 49.4% female
  • 21.4% 65 years and older​


  • 9% 16 to 55 years
  • 8% 55 years and older
  • 4% 65 years and older​
  • 3% 75 years and older

The most frequent underlying medical conditions were obesity (35.1%), diabetes (8.4%), and pulmonary disease (7.8%).

SOURCE: CDC - ttps:// (April 15, 2021)