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May 18, 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 significant 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 harmless spike-shaped proteins that will protect against a COVID-19 infection. While these vaccines use new technology, researchers have been studying them for decades.

The Johnson & Johnson/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 significant protection from serious illness and hospitalization. Getting vaccinated against COVID-19 and following CDC’s recommendations to protect yourself and others will offer the best protection from COVID-19.

The Moderna vaccine is recommended for people age 18+ and includes 2 shots spaced 28 days apart. It is a messenger RNA, or mRNA, vaccine. Based on evidence from clinical trials, the Moderna vaccine was 94% effective at preventing COVID-19 and provides significant protection against serious illness.

The Pfizer-BioNTech vaccine is recommended for people aged 12+ and includes 2 shots spaced 21 days apart. It is an mRNA vaccine. Based on evidence from clinical trials, the Pfizer-BioNTech vaccine was 95% effective at preventing COVID-19 and provides significant protection against serious illness.

The Johnson & Johnson/Janssen vaccine is delivered in one shot only. It is a viral vector vaccine. Based on evidence from clinical trials, the Johnson & Johnson vaccine was 72% effective at preventing COVID-19 and provides significant protection against serious illness. Health officials are closely monitoring all vaccines for safety, including the Johnson & Johnson vaccine.

Having multiple vaccines 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?

All COVID-19 vaccines currently available in the United States have been shown to be highly effective at preventing 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.

If you receive a Pfizer or Moderna COVID-19 vaccine, you will need 2 shots to get the most protection. The second shot of the Moderna vaccine should be given 28 days after your first shot, and the second shot of the Pfizer vaccine should be given 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 2 weeks after receiving 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 appropriate time.

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

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. We are still learning exactly how effective the vaccines are against new variants of the virus that causes COVID-19.

More about virus variants (CDC)