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How do COVID-19 vaccines keep us safe?

Last Updated

April 12, 2021

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

Vaccines are the best protection we have against many serious illnesses. They protect us from diseases by teaching our immune systems how to fight viruses and infections — without actually getting sick from the disease.

COVID-19 can have serious and life-threatening complications, which is why it’s important for everyone who’s eligible to get vaccinated. If you’re not sure, ask your doctor if you should be immunized against COVID-19.

What is a vaccine?

A vaccine is a protective treatment that helps your immune system learn how to defend against a virus or other pathogen — without using the virus or risking that it will infect you.

Most vaccines for COVID-19 teach your body to protect against the harmless spike-shaped protein on the outside of the coronavirus.

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How do these vaccines protect me?

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 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.

How vaccines work (
Why should I get vaccinated?

Getting immunized against COVID-19 will keep most people from getting sick. Even in a rare case where one does catch the virus, the vaccine will likely prevent you from becoming seriously ill.

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

We are still learning how the vaccine affects whether people can still transmit COVID-19 to others. It may be possible that a vaccinated person can still carry the virus and infect others, even if that person does not appear to be sick.

That’s why, until enough Americans are vaccinated to fight off COVID-19, we will need to keep wearing masks, stay 6 feet apart from people we don’t live with, avoid crowds, and wash our hands frequently.

More things to know about vaccines (Johns Hopkins Coronavirus Resource Center)
How long does a COVID-19 vaccine last?

Immunization against COVID-19 will help protect you for the near future, but it’s still not clear how long the protection will last. We will have a clearer picture of how long immunity lasts in years to come when we have collected more data. Both natural immunity and immunity from the vaccine are important ways to fight COVID-19 that experts are trying to learn more about, and places like the CDC will keep the public informed as new evidence becomes available.

More about vaccine immunity (CDC)
What if I have an underlying health condition?

People with underlying medical conditions can receive the FDA-authorized COVID-19 vaccines. In fact, vaccination is especially important for adults of any age with certain underlying medical conditions, like diabetes and high blood pressure, because they are at increased risk for severe illness from COVID-19. Ask your doctor if you have specific questions.

People who have autoimmune conditions and who have previously had Guillan-Barre syndrome or Bell’s palsy may receive a COVID-19 vaccine.

More about underlying conditions (CDC)