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.
HOW COVID-19 VACCINES WORK
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 vaccines have been shown to do a very good job of:
- Preventing infection with the SARS-CoV-2 virus, which causes COVID-19
- Protecting against serious illness, hospitalization, and death from COVID-19
- Reducing the risk of people spreading COVID-19
The first COVID-19 vaccines approved in the United States are called mRNA vaccines. They work differently from many 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.
- If you get the Pfizer COVID-19 vaccine, you should get your second shot about 21 days (3 weeks) after the first shot.
- If you get the Moderna COVID-19 vaccine, you should get your second shot about 28 days (4 weeks) after the first shot.
- The day you get your first shot, you will likely be able to schedule the date for your second shot.
- It takes time for your immune system to start protecting you after receiving the vaccine. You are considered fully vaccinated 2 weeks after your second dose.
- Over 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.
VIRAL VECTOR VACCINES
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 Johnson and Johnson's Janssen (J&J/Janssen) COVID-19 vaccine 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.
- It takes time for your immune system to start protecting you after receiving the vaccine. You are considered fully vaccinated 2 weeks after your shot.
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
VACCINE SIDE EFFECTS
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, redness, or swelling on the arm where you got the shot
- Muscle pain
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.
HOW TO GET THE VACCINE
There are several ways you can look for vaccination providers near you.
- Go to the CDC VaccineFinder.
- Text your zip code to 438829 or call 1-800-232-0233 to find vaccine locations near you.
- Check your local pharmacy's website to see if vaccination appointments are available. Find out which pharmacies are participating in the Federal Retail Pharmacy Program.
- Contact your state health department to find additional vaccination locations in the area.
- Check your local news outlets. They may have information on how to get a vaccination appointment.
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 have 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
There have been reports of rare blood clots with low platelets mainly in women younger than 50 years old after receiving Johnson & Johnson's Janssen (J&J/Janssen) vaccine. The CDC and FDA recommend continued use of this vaccine because:
- This risk is extremely rare (occurred in 7 women out of 1 million vaccinated).
- The benefits of the vaccine are much greater than the potential risks.
Women age 50 and younger who have received the J&J vaccine should be aware of these possible side effects for 3 weeks after getting the shot:
- Severe or persistent headaches or blurred vision
- Shortness of breath
- Chest pain
- Leg swelling
- Persistent abdominal pain
- Easy bruising or tiny blood spots under the skin beyond the injection site
If you notice any of these symptoms, seek medical care right away.
To learn more about COVID-19 vaccine safety, go to the CDC web site:
- Ensuring COVID-19 Vaccine Safety in the United States -- www.cdc.gov/coronavirus/2019-ncov/vaccines/safety.html
- V-Safe After Vaccination Health Checker -- www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/vsafe.html
- 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
WHAT YOU CAN DO ONCE YOU ARE FULLY VACCINATED
Fully-vaccinated people can resume activities without wearing a mask or physically distancing, except where required by federal, state, local, tribal, or territorial laws, rules, and regulations, including local business and workplace guidance.
The CDC has recommendations for what it is safe to do once you are fully vaccinated https://www.cdc.gov/coronavirus/2019-ncov/vaccines/fully-vaccinated.html.
We are still learning how well vaccines help prevent COVID-19 from spreading and how long the protection they provide lasts. Until more is known, using vaccines, masks, and taking other steps to help protect others is the best way to stay safe and healthy.
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Review Date 5/14/2021
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.