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September 9, 2021

How do the COVID-19 vaccines protect me?

The answers on this site were developed with and vetted by the CDC

When we get a vaccine, it activates our immune response. This helps our bodies learn to fight off the virus without the danger of an actual infection. If we are exposed to the virus in the future, our immune system “remembers” how to fight it. All authorized COVID-19 vaccines provide strong protection against serious illness and hospitalization due to COVID-19.

The Moderna and Pfizer vaccines use messenger RNA, or mRNA. mRNA vaccines do not contain a live virus. They give our bodies “instructions” for how to make and fight the spike-shaped proteins that will protect against a COVID-19 infection. While these vaccines use new technology, researchers have been studying them for decades.

Johnson & Johnson’s Janssen vaccine is a viral vector vaccine and also does not contain a live virus. It uses a harmless adenovirus to create a spike protein that the immune system responds to, creating antibodies to protect against COVID-19.

None of these vaccines can give you COVID-19.

It takes time for your body to build immunity after vaccination, so you won’t have full protection until 2 weeks after your final dose.

Dr Angelica Kottkamp Video
How vaccines work (vaccines.gov)

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What are the differences between the vaccines?

All authorized COVID-19 vaccines provide strong protection from serious illness and hospitalization. Getting vaccinated and following CDC’s recommendations to take care of yourself and others is the best way to protect against COVID-19.

The Pfizer-BioNTech vaccine (Comirnaty) is authorized for people 12 years and over. It is an mRNA vaccine and includes two shots spaced 21 days apart. As of August 2021 the Pfizer vaccine is fully approved by the FDA. The Pfizer-BioNTech vaccine is 91% effective at preventing COVID-19 and provides strong protection against serious illness.

The Moderna vaccine is authorized for people 18 years and over. It is a messenger RNA, or mRNA, vaccine and includes two shots spaced 28 days apart. Clinical trials showed the Moderna vaccine was 94% effective at preventing COVID-19 and provides strong protection against serious illness.

Johnson & Johnson’s Janssen vaccine is authorized for people 18 years and over. It is a viral vector vaccine and only requires one shot. Clinical trials showed the Johnson & Johnson vaccine was 72% effective at preventing COVID-19 and provides strong protection against serious illness. Health officials are closely monitoring all vaccines for safety, including the Johnson & Johnson vaccine.

Having multiple types of vaccines available is crucial so that vaccination programs can quickly reach as many people as possible.

Different vaccines work (CDC)
If you’re ready to get vaccinated, get up-to-date information on locations near you.
Do I need one shot or two?

Research shows all COVID-19 vaccines currently available in the United States are very effective at preventing COVID-19. After vaccination, it takes time for your body to build immunity, so you won’t have full protection until two weeks after your final dose.

If you get a Pfizer or Moderna COVID-19 vaccine, you will need two shots to get the most protection. You should get the second shot of the Moderna vaccine 28 days after your first shot. You should get the second shot of the Pfizer vaccine 21 days after your first shot.

COVID-19 vaccines are not interchangeable. If you received a Pfizer-BioNTech or Moderna COVID-19 vaccine, you should get the same type for your second shot. If you are told you need two shots, make sure that you get both of them.

Johnson & Johnson’s Janssen vaccine only requires one shot. People who receive the Johnson & Johnson vaccine are considered fully vaccinated two weeks after they get the single shot.

Ask your healthcare provider about tools like V-safe that can send you automated reminders about getting your first and second shots at the right time.

What to expect at your appointment (CDC)
Do the vaccines protect against the Delta variant?

The COVID-19 vaccines available in the United States are very effective at preventing severe disease and death, including against the Delta variant. Vaccines also reduce a person’s risk of getting the virus. But they are not 100% effective and some fully vaccinated people will become infected (called a breakthrough infection) and experience illness. When that happens, the vaccines still provide strong protection against serious illness and death.

The Delta variant is currently responsible for more than 90% of COVID cases in the United States. The Delta variant is also very contagious — more than 2X contagious as the original virus. People who have not been fully vaccinated against COVID-19 are most at risk and more likely to transmit the virus to others.

So far, studies also suggest that all vaccines authorized for use in the United States are effective against other known variants. There are currently 4 notable variants in the United States:

  • B.1.1.7 (Alpha)
  • B.1.351 (Beta)
  • P.1 (Gamma)
  • B.1.617.2 (Delta)
Delta Variant: What We Know About the Science (CDC)
What should I know about breakthrough infections?

COVID-19 vaccines are an effective and critical tool to bring the pandemic under control. However, no vaccines are 100% able to prevent illness. Some fully vaccinated people will get sick. Some will even be hospitalized or die from COVID-19. Fortunately, the risk of infection, hospitalization, and death are all much lower for people who are vaccinated, compared to unvaccinated people.

If you are fully vaccinated and do get COVID-19, you will still be protected against getting seriously ill or being hospitalized.

The Possibility of COVID-19 after Vaccination: Breakthrough Infections (CDC)

Looking for a vaccine? Visit the Vaccine Finder to get up-to-date information on locations near you.


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