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October 17, 2022

How do the COVID-19 vaccines protect me?

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

COVID-19 vaccines are a critical tool to bring the pandemic under control. The risk of severe disease and death are all much lower for people who are vaccinated, compared to unvaccinated people. All authorized COVID-19 vaccines provide strong protection against serious illness and hospitalization due to COVID-19.

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.

The Moderna and Pfizer-BioNTech 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 does not contain a live virus either. It uses a harmless adenovirus to create a spike protein that the immune system responds to, creating antibodies to protect against COVID-19.

The Novavax vaccine is a protein-based vaccine, and includes harmless pieces (proteins) of the virus that causes COVID-19. These proteins are commonly referred to as the spike protein of the virus. After receiving this vaccine, the body creates an immune response to these proteins and proceeds to discard all of the vaccine ingredients - including the spike protein - as it would discard any substance that the body no longer needs.

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 most recent dose.

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How vaccines work (

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What are the differences between the vaccines?

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. CDC and other health experts are currently recommending mRNA vaccines (Pfizer-BioNTech and Moderna) as the preferred vaccines to protect against new variants.

The Pfizer-BioNTech vaccine (Comirnaty) is authorized for people 6 months and older. It’s a messenger RNA, or mRNA, vaccine and includes two shots spaced 21 days apart. This vaccine was fully approved by the FDA for ages 16 and older in August 2021. It’s also available for ages 5 to 15 under emergency use authorization (and is being given in smaller doses to children age 5 to 11).

The Moderna vaccine is now authorized by the FDA for children ages 6 months and up, and approved for adults 18 years and over. It’s also an mRNA vaccine and includes two shots spaced 28 days apart. Clinical trials showed the Moderna vaccine also provides strong protection against serious illness.

For people who are unable or unwilling to receive an mRNA vaccine, the Johnson & Johnson Janssen and Novavax vaccines are authorized and available for people 18 years and over. Johnson & Johnson’s is a viral vector vaccine and only requires one shot, while Novavax is a protein-based vaccine that requires two shots 3 to 8 weeks apart.

Different vaccines work (CDC)
If you’re ready to get vaccinated, get up-to-date information on locations near you.
Do the vaccines protect against the variants?

Staying up to date with COVID vaccines provides strong protection against severe disease and death when it comes to new variants. This includes booster shots at the appropriate time. Vaccines also reduce a person’s risk of getting the virus. But no vaccine is 100% effective and some fully vaccinated people will become infected and experience illness. This is called a breakthrough infection. When one happens, the vaccines still provide strong protection against serious illness and death.

Recent COVID variants are extremely contagious — more than twice as contagious as the original virus. As of September 2022, the FDA and CDC have authorized an updated booster shot that is designed around spike protein components of Omicron BA.4 and BA.5 and provides stronger protection against these circulating variants. CDC recommends that everyone age 5 and older should receive an updated booster shot.

What You Need to Know about Variants (CDC)
What should I know about breakthrough infections?

COVID-19 vaccines are an effective tool to bring the pandemic under control. No vaccines are 100% able to prevent illness. Fortunately, the risk of serious illness, hospitalization, and death are all much lower if you’re vaccinated.

Recent data shows that vaccine effectiveness decreases over time. New variants are also even more infectious than the original virus. This leads to more breakthrough cases among those vaccinated. Vaccination still helps protect against serious illness and death. Because of this, CDC recommends that everyone age 5 and older receive a booster shot at the appropriate time.

The Possibility of COVID-19 after Vaccination: Breakthrough Infections (CDC)
What are mRNA vaccines and how do they work?

Many vaccines put a weakened or inactivated germ into your body to build immunity. But messenger RNA (mRNA) vaccines teach your cells how to make a protein that will trigger an immune response inside your body. This produces antibodies that protect you if the real virus were to enter your body. Since mRNA vaccines don't use an actual virus, they can be safely produced in large quantities faster than other vaccines.

The Moderna and Pfizer-BioNTech vaccines use mRNA. While these vaccines use new technology, researchers have been working with mRNA vaccines for decades. mRNA vaccines were studied before for flu, Zika, rabies, and cytomegalovirus (CMV).

mRNA never enters the nucleus of the cell where DNA is located, so it cannot change your genes. Our cells break down mRNA and get rid of it within a few days after vaccination.

Understanding mRNA COVID-19 Vaccines (CDC)
What are the benefits of getting vaccinated for COVID-19?

Being up to date with COVID-19 vaccines drastically reduces the likelihood that you will get seriously ill from COVID-19. If you do get infected, vaccines also greatly reduce the chances of dying from the disease. And, if you're vaccinated and do get COVID-19, recent data suggests that you would spread the virus for a shorter time.

Most side effects from the vaccine are mild (redness or swelling of the injection site) and go away within a few days. If you want to know more about COVID-19 vaccine safety, please refer to our “How do we know they’re safe?” FAQ section.

Protecting yourself protects those around you, such as people at increased risk of severe illness from COVID-19. It also helps protect those who can’t get vaccinated, including infants, or people with immune systems weakened by things like chemotherapy for cancer.

More things to know about vaccines (Johns Hopkins Coronavirus Resource Center)

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

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