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Vaccine Basics

cov-whygetvaccine.jpgGetting vaccinated is one of many steps you can take to protect yourself and others from COVID-19. Protection from COVID-19 is critically important because, for some people, it can cause severe illness or death.

Stopping a pandemic requires using all the tools available. Vaccines work with your immune system so your body will be ready to fight the virus if you are exposed. Other steps, like masks and social distancing, help reduce your chance of being exposed to the virus or spreading it to others. Together, COVID-19 vaccination and following public health recommendations to protect yourself and others will offer the best protection from COVID-19.

Table of Contents

Vaccines Status

Four COVID-19 vaccines are authorized or approved for use in the United States to prevent COVID-19. Pfizer-BioNTech or Moderna (COVID-19 mRNA vaccines) are preferred. You may soon be able to get Noravax. The Johnson & Johnson's Janssen COVID-19 vaccine is available in some situations

Pfizer-BioNTech COVID-19 Vaccine: This vaccine, marketed as Comirnaty, is for the prevention of COVID-19 disease in individuals 6 months of age and older.

For adults, this is a two-dose vaccine, given 3-8 weeks apart. Clinical trial data show the vaccine is 95 percent effective at preventing COVID-19 infection starting 7 days after the second dose. Individuals are not considered fully protected until 1 to 2 weeks after they receive the second dose.

Pfizer-BioNTech COVID-19 Vaccine continues to be available under emergency use authorization (EUA) for children and teens 6 months through 15 years, for the administration of a third dose in certain immunocompromised people, for a single booster dose in 5 and up, and for a second booster dose in certain people.

For children 6 months through 4 years, a three-dose Pfizer vaccine series is recommended. For children and teens ages 5 to 17 years, a two-dose primary series is recommended.

Moderna COVID-19 Vaccine: Moderna COVID-19 vaccine is approved for use in individuals aged 18 years and older and is authorized for ages 6 months and older given in a two-dose primary series.

Johnson & Johnson – Janssen COVID-19 Vaccine: This single-dose vaccine is authorized for emergency use in individuals aged 18 years and older. Full protection begins 1 to 2 weeks after getting the vaccine. This vaccine is not authorized for people under age 18.

Novavax Vaccine: On July 19, 2022, the CDC Advisory Committee on Immunization Practices recommended that Novavax’s COVID-19 vaccine be used as another primary series option for adults ages 18 years and older. Novavax’s COVID-19 vaccine, which will be available in the coming weeks, was built on a familiar type of COVID-19 vaccine technology.

Large-scale clinical trials continue to be in progress or being planned for COVID-19 vaccines in the United States. To learn more about U.S. COVID-19 vaccine clinical trials including vaccines in earlier stages of development, visit

Third Doses and Booster Doses

For information on third doses and boosters, visit the Centers for Disease Control and Prevention (CDC). Use the CDC’s COVID-19 booster tool to learn if and when your child or teen can get boosters to stay up to date with their COVID-19 vaccines.

Why Should You Get Vaccinated?

  • It's safe, simple, and free of charge.
  • It could keep you from getting COVID-19. If you still get COVID-19, it could keep you from becoming seriously ill.
  • It will help you do your part to slow the spread of COVID-19 and protect the health of your family, your friends and your community.
  • It's an mRNA vaccine. These types of vaccines have been studied for more than two decades to evaluate their safety and effectiveness.
  • It's the first step to returning to normal.

Why Should You Get Vaccinated? Download Posters:

Download The Facts About COVID-19 Vaccines and FAQs and Key Messages about the COVID-19 Vaccine for Communities.

Before and After Vaccination

We’re still learning how vaccines will affect the spread of COVID-19. If it has been less than 2 weeks since your shot, or if you still need to get your second dose, you are NOT fully protected. Keep taking all prevention steps, such as washing your hands, wearing a mask, staying six feet apart, and limiting gatherings, until you are fully vaccinated. Based on what we know about COVID-19 vaccines, people who have been fully vaccinated can resume activities they did before the pandemic.

Learn more from When You've Been Fully Vaccinated from the Centers for Disease Control and Prevention (CDC).

Visit Prevention and Treatment for more information.

Vaccine Safety

The U.S. vaccine safety system ensures that all vaccines are as safe as possible. Safety is a top priority while federal partners work to make COVID-19 vaccines available.

How the COVID-19 Vaccine Works

To understand how COVID-19 vaccines work, it helps to first look at how our bodies fight infection. When germs, such as viruses, invade the body, they attack and multiply. This invasion, called an infection, is what causes illness. The immune system uses several tools to fight infection. The first time the body encounters a germ, it can take several days to make and use all the germ-fighting tools needed to get over the infection. After the infection, the immune system remembers what it learned about how to protect the body against that disease. Vaccines help develop immunity by imitating an infection. Vaccines greatly reduce the risk of infection by working with the body’s natural defenses to safely develop immunity to disease.

COVID-19 vaccines will help our bodies develop immunity to the virus that causes COVID-19 without us having to get the illness. Different types of vaccines work in different ways to teach the immune system how to recognize a germ without getting sick and be ready to quickly attack the germ if we are exposed to the germ. It takes about two weeks after completing a vaccine series before your body makes an immune response to protect against infection and illness.

Most COVID-19 vaccines will require two doses spaced 3 to 8 weeks apart. People will need both doses to be protected. It is possible that a person could be infected with the virus that causes COVID-19 just before or just after vaccination and then get sick because the vaccine did not have enough time to provide protection or because someone did not get both recommended vaccine doses.

Side Effects

Most people do not have serious problems after being vaccinated. Side effects may feel like flu and even affect your ability to do daily activities, but they should go away in a few days. Often times, people will have symptoms like mild fever, tiredness, and body aches after getting a vaccine. These symptoms are normal and signal your body’s immune response to the vaccine to help you prevent future infections. For more information, visit What to Expect After Getting a COVID-19 Vaccine.

Page last updated: March 23, 2023