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COVID-19 vaccines

COVID-19 vaccines are used to boost the body's immune system and protect against COVID-19. These vaccines are a vital tool to help stop the COVID-19 pandemic.



COVID-19 vaccines protect people from getting COVID-19. These vaccines "teach" your body how to defend against the SARS-CoV-2 virus, which causes COVID-19.

COVID-19 vaccine

The first COVID-19 vaccines approved in the United States are called mRNA vaccines. They work differently from other vaccines.

  • COVID-19 mRNA vaccines use messenger RNA (mRNA) to tell cells in the body how to briefly create a harmless piece of "spike" protein that is unique to the SARS-CoV-2 virus. Cells then get rid of the mRNA.
  • This "spike" protein triggers an immune response inside your body, making antibodies that protect against COVID-19. Your immune system then learns to attack the SARS-CoV-2 virus if you are ever exposed to it.
  • There are two mRNA COVID-19 vaccines currently approved for use in the United States, the Pfizer-BioNTech and the Moderna COVID-19 vaccines.

The COVID-19 mRNA vaccine is given as an injection (shot) in the arm in 2 doses.

  • You will receive the second shot in about 3 to 4 weeks after getting the first shot. You need to get both shots for the vaccine to work.
  • The vaccine won't start to protect you until about 1 to 2 weeks after the second shot.
  • Around 90% of people who receive both shots will NOT become ill with COVID-19. Those who do become infected with the virus will likely have a milder infection.


These vaccines are also effective at protecting against COVID-19.

  • They use a virus (a vector) that has been changed so that it can't harm the body. This virus carries instructions that tell the cells of the body to create the "spike" protein unique to the SARS-CoV-2 virus.
  • This triggers your immune system to attack the SARS-CoV-2 virus if you are ever exposed to it.
  • The viral vector vaccine does not cause infection with the virus that is used as vector or with the SARS-CoV-2 virus.
  • The Janssen COVID-19 vaccine (produced by Johnson and Johnson) is a viral vector vaccine. It has been approved for use in the United States. You only need one shot for this vaccine to protect you against COVID-19.

COVID-19 vaccines do not contain any live virus, and they cannot give you COVID-19. They also never affect or interfere with your genes (DNA).

While most people who get COVID-19 also develop protection against getting it again, no one knows how long this immunity lasts. The virus can cause serious illness or death and can spread to other people. Getting a vaccine is a far safer way to protect against the virus than relying on immunity due to an infection.

Other vaccines are being developed that use different methods to protect against the virus. To get up-to date information about other vaccines being developed, go to the Centers for Disease Control and Prevention (CDC) website:

Different COVID-19 vaccines - www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines.html

To get up-to-date information about the COVID-19 vaccines approved for use, please see the United States Food and Drug Administration (FDA) website:

COVID-19 Vaccines - www.fda.gov/emergency-preparedness-and-response/coronavirus-disease-2019-covid-19/covid-19-vaccines


While COVID-19 vaccines will not make you sick, they may cause certain side effects and flu-like symptoms. This is normal. These symptoms are a sign that your body is making antibodies against the virus. Common side effects include:

  • Pain and swelling on the arm where you got the shot
  • Fever
  • Chills
  • Tiredness
  • Headache

Symptoms from the shot may make you feel bad enough that you need to take time off from work or daily activities, but they should go away within a few days. Even if you do have side effects, it is still important to get the second shot. Any side effects from the vaccine are far less dangerous than the potential for serious illness or death from COVID-19.

If symptoms do not go away in a few days, or if you have any concerns, you should contact your health care provider.


Currently there are limited supplies of the COVID-19 vaccine. Because of this, the CDC has made recommendations to state and local governments about who should get vaccines first. Exactly how the vaccine is prioritized and distributed for administration to people will be determined by each state. Check with your local public health department for information in your state.

These recommendations will help achieve several goals:

  • Reduce the number of people dying from the virus
  • Reduce the number of people who get sick from the virus
  • Help society continue to function
  • Reduce the burden on the health care system and on people who are more greatly affected by COVID-19

The CDC recommends that the vaccine be rolled out in phases.

Phase 1a includes the first groups of people who should get the vaccine:

  • Health care personnel -- This includes anyone who may have direct or indirect exposure to patients with COVID-19.
  • Residents of long-term care facilities, because they are most at risk of dying from COVID-19.

Phase 1b includes:

  • Essential frontline workers, such as firefighters, police officers, teachers, grocery store workers, United States Postal workers, public transit workers, and others
  • People age 75 years and older, because people in this group are at high risk for illness, hospitalization, and death from COVID-19

Phase 1c includes:

  • People ages 65 to 74 years
  • People ages 16 to 64 years with certain underlying medical conditions including cancer, COPD, Down syndrome, weak immune system, heart disease, kidney disease, obesity, pregnancy, smoking, diabetes, and sickle cell disease
  • Other essential workers, including people who work in transportation, food service, public health, housing construction, public safety, and others

As the vaccine becomes widely available, more of the general population will be able to get vaccinated.

You can find out more about recommendations for the vaccine roll out in the United States on the CDC web site:

CDC's COVID-19 Vaccine Rollout Recommendations -- www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations.html


The safety of vaccines is the top priority, and COVID-19 vaccines have passed rigorous safety standards before approval.

COVID-19 vaccines are based on research and technology that has been around for decades. Because the virus is widespread, many tens of thousands of people are being studied to see how well the vaccines work and how safe they are. This has helped allow the vaccines to be developed, tested, studied, and processed for use very quickly. They continue to be closely monitored to ensure they are safe and effective.

There have been reports of some people who have had an allergic reaction to the current vaccines. So it is important to follow certain precautions:

  • If you have ever had a severe allergic reaction to any ingredient in a COVID-19 vaccine, you should not get one of the current COVID-19 vaccines.
  • If you have ever had an immediate allergic reaction (hives, swelling, wheezing) to any ingredient in the COVID-19 vaccine, you should not get one of the current COVID-19 vaccines.
  • If you have a severe or non-severe allergic reaction after getting the first shot of the COVID-19 vaccine, you should not get the second shot.

If you have had an allergic reaction, even if not severe, to other vaccines or injectable therapies, you should ask your doctor if you should get a COVID-19 vaccine. Your doctor will help you decide if it is safe for you to get vaccinated. Your doctor may refer you to a specialist in allergies and immunology to provide more care or advice.

CDC recommends that people may still get vaccinated if they have a history of:

  • Severe allergic reactions NOT related to vaccines or injectable medicines -- such as food, pet, venom, environmental, or latex allergies
  • Allergies to oral medicines or a family history of severe allergic reactions

To learn more about COVID-19 vaccine safety, go to the CDC web site:


Even after you receive both doses of the vaccine, you will still need to continue to wear a mask, stay at least 6 feet away from others, and wash your hands often.

Experts are still learning about how COVID-19 vaccines provide protection, so we need to continue to do all that we can to stop the spread. For example, it is not known if a person who is vaccinated could still spread the virus, even though they are protected from it.

For this reason, until more is known, using both vaccines and steps to protect others are the best way to stay safe and healthy.

Alternative Names

Vaccines for COVID-19; COVID - 19 vaccinations; COVID - 19 shots; Vaccinations for COVID - 19; COVID - 19 immunizations; COVID - 19 prevention - vaccines; mRNA vaccine-COVID


Centers for Disease Control and Prevention website. Benefits of getting a COVID-19 vaccine. www.cdc.gov/coronavirus/2019-ncov/vaccines/vaccine-benefits.html. Updated January 5, 2021. Accessed March 3, 2021.

Centers for Disease Control and Prevention website. CDC’s COVID-19 vaccine rollout recommendations. www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations.html. Updated February 19, 2021. Accessed March 3, 2021.

Centers for Disease Control and Prevention website. Different COVID-19 vaccines. www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines.html. Updated March 3, 2021. Accessed March 3, 2021.

Centers for Disease Control and Prevention website. Interim clinical considerations for use of mRNA COVID-19 vaccines currently authorized in the United States. www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html. Updated February 10, 2021. Accessed March 3, 2021.

Centers for Disease Control and Prevention website. Myths and facts about COVID-19 vaccines. www.cdc.gov/coronavirus/2019-ncov/vaccines/facts.html. Updated February 3, 2021. Accessed March 3, 2021.

Centers for Disease Control and Prevention website. Understanding viral vector COVID-19 vaccines. www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/viralvector.html. Updated March 2, 2021. Accessed March 3, 2021.

Centers for Disease Control and Prevention website. What to do if you have an allergic reaction after getting a COVID-19 vaccine. www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/allergic-reaction.html. Updated February 25, 2021. Accessed March 3, 2021.

Review Date 1/6/2021

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. Editorial update 03/03/2021.