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COVID-19 Vaccines Work

COVID-19 Vaccines Work

After the U.S. Food and Drug Administration (FDA) approves a vaccine or authorizes a vaccine for emergency use, experts continue to assess vaccine effectiveness—or how a vaccine works in real-world conditions.  The goal is to understand how a vaccine protects people outside of strict clinical trial settings.

What you need to know

  • Vaccines currently approved for use in the United States are effective at preventing COVID-19.
  • COVID-19 vaccination is an important tool to help stop the pandemic.
  • COVID-19 vaccines help protect people who are vaccinated from getting sick or severely ill with COVID-19 and may also help protect people around them.
  • CDC recommends you get a COVID-19 vaccine as soon as one is available to you.

So far, research on mRNA COVID-19 vaccine effectiveness in real-world conditions is reassuring.

  • Research provides growing evidence that Pfizer-BioNTech and Moderna mRNA COVID-19 vaccines offer similar protection in real-world conditions as in clinical trial settings.
  • Real-world data show that receiving only one dose of these mRNA COVID-19 vaccines provides some protection against COVID-19, at least in the short term.
  • To receive the most protection, people receiving one of these mRNA COVID-19 vaccines should receive both recommended doses.
  • In addition to providing protection against COVID-19, there is increasing evidence that these mRNA COVID-19 vaccines provide protection against infections that do not result in symptoms.

COVID-19 vaccines will help protect you from getting sick or severely ill with COVID-19

  • Large-scale clinical trials found that COVID-19 vaccination prevented most people from getting COVID-19.
  • All COVID-19 vaccines available in the United States are effective at preventing COVID-19.
  • It typically takes about two weeks for the body to build protection after vaccination. That means it is possible you could still get COVID-19 soon after vaccination. This is because your body has not had enough time to build full protection.
  • Some people who are fully vaccinated against COVID-19 will still get sick because the vaccines are not 100% effective. When this happens, vaccination might help keep you from getting seriously ill, based on data from clinical studies.

COVID-19 vaccines and new variants of the virus

What We Know

New variants of the virus that causes COVID-19 are spreading in the United States. Current data suggest that COVID-19 vaccines authorized for use in the United States offer protection against most variants. However, some variants might cause illness in some people after they are fully vaccinated.

What We Do Not Know

Evidence is limited on how the new COVID-19 variants will affect how COVID-19 vaccines work in real-world conditions. CDC has systems in place to monitor how common these variants are and to look for the emergence of new variants. CDC will continue to monitor variants to see if they have any impact on how COVID-19 vaccines work in real-world conditions.

More details: Learn more about COVID-19 variants.