COVID-19 vaccines: Get the facts

By Mayo Clinic Staff

As the coronavirus disease 2019 (COVID-19) pandemic continues, you might have questions about COVID-19 vaccines. Find out about the different types of COVID-19 vaccines, how they work, the possible side effects, and the benefits for you and your family.

Staying up to date with a COVID-19 vaccine can:

• Help prevent serious illness and death due to COVID-19 for both children and adults.
• Help prevent you from needing to go to the hospital due to COVID-19.
• Boost your body’s protection, also called immunity, against catching the COVID-19 virus.
• Be a safer way to protect yourself compared with getting sick with the COVID-19 virus.

How much protection a COVID-19 vaccine gives depends on different factors. Factors that can affect how much you’re protected with a vaccine can include your age, if you’ve had COVID-19 before or if you have medical conditions such as cancer.

How well a COVID-19 vaccine protects you also depends on how the virus that causes COVID-19 changes and what variants the vaccine protects against. Your level of protection also depends on timing, such as when you got the shot.

Talk to your health care team about how you can stay up to date with COVID-19 vaccines.

Yes. After you’ve had COVID-19, getting vaccinated can boost your body’s protection against catching the virus that causes COVID-19 another time.

Getting COVID-19 or getting a COVID-19 vaccination gives you protection, also called immunity, from being infected again with the virus that causes COVID-19. But over time, that protection seems to fade. Getting COVID-19 again may cause serious illness or medical complications, especially for people with risk factors for severe COVID-19.

Researchers continue to study what happens when someone has COVID-19 a second time. But some people may see their risk of having to go to the hospital and having medical problems such as diabetes go up with each COVID-19 infection.

Research has found that people who have had COVID-19 and then have had all of the suggested COVID-19 vaccinations are less likely to be treated in the hospital due to COVID-19 than people who are unvaccinated or who haven’t had all the suggested shots. This protection wears off in the months after getting the vaccine.

Also, because the virus that causes COVID-19 can change, also called mutate, a vaccination with the latest strain, or variant, that is spreading or expected to spread can help keep you from getting sick again.

Three COVID-19 vaccines are available in the United States. They are:

• 2023-2024 Pfizer-BioNTech COVID-19 vaccine, available for people age 6 months and older.
• 2023-2024 Moderna COVID-19 vaccine, available for people age 6 months and older.
• 2023-2024 Novavax COVID-19 vaccine, available for people age 12 years and older.

At the start of the COVID-19 pandemic, COVID-19 vaccines were needed right away. But the vaccine approval process that the U.S. Food and Drug Administration (FDA) follows can take years.

To provide vaccines sooner, the FDA gave emergency use authorization to COVID-19 vaccines. This authorization is based on less data than is typically required. But the data still has to show that the vaccines are safe and effective.

In August 2022, the FDA authorized an update to the Moderna and the Pfizer-BioNTech COVID-19 vaccines. Both included the original and omicron variants of the virus that causes COVID-19. In one analysis, the vaccines were up to 62% effective at keeping adults with COVID-19 from needing COVID-19 care in the hospital.

In June 2023, the FDA directed vaccine makers to update COVID-19 vaccines. The vaccines were changed to target a strain of the virus that causes COVID-19 called XBB.1.5.

In September and October 2023, the FDA authorized the use of the updated 2023-2024 COVID-19 vaccines made by Novavax, Moderna and Pfizer-BioNTech.

Vaccines with FDA emergency use authorization or approval include:

• 2023-2024 Pfizer-BioNTech COVID-19 vaccine. This vaccine was first tested against the original strain of the COVID-19 virus. That strain began spreading at the end of 2019. In December 2020, the Pfizer-BioNTech COVID-19 vaccine two-dose series was found to be both safe and 91% to 95% effective in preventing COVID-19 infection in people age 18 and older. This data helped predict how well the vaccines would work for younger people. The effectiveness varied by age.

  The Pfizer-BioNTech vaccine is approved under the name Comirnaty for people age 12 and older. It is authorized for people age 6 months to 11 years. The number of shots in this vaccination series varies based on a person’s age and COVID-19 vaccination history.

• 2023-2024 Moderna COVID-19 vaccine. This vaccine also was first tested against the original strain of the virus that causes COVID-19. In December 2020, the Moderna COVID-19 vaccine was found to be both safe and about 93% effective in preventing infection among study volunteers, all age 18 or older.

  Based on the comparison between people who got COVID-19 in the placebo group, the Moderna COVID-19 vaccine was 98% effective at preventing serious COVID-19 illness. Vaccine effect was predicted for younger people based on that clinical trial data as well.

  The vaccine is approved under the name Spikevax for people age 12 and older. The vaccine is authorized for use in people age 6 months to 11 years. The number of shots needed varies based on a person’s age and COVID-19 vaccination history.

• 2023-2024 Novavax COVID-19 vaccine, adjuvanted. This vaccine is available under an emergency use authorization for people age 12 and older. It requires two shots, given 3 to 8 weeks apart. Research done before the spread of the delta and omicron variants has shown that the vaccine is 90% effective at preventing mild, moderate and severe disease with COVID-19. For people age 65 and older, the vaccine is 79% effective.

In general, people age 5 and older with typical immune systems can get any vaccine that is approved or authorized for their age. They usually don’t need to get the same vaccine each time.

Some people should get all their vaccine doses from the same vaccine maker, including:

• Children ages 6 months to 4 years.
• People age 5 years and older with weakened immune systems.
• People age 12 and older who have had one shot of the Novavax vaccine should get the second Novavax shot in the two-dose series.

Talk to your healthcare professional if you have any questions about the vaccines for you or your child. Your healthcare team can help you if:

• The vaccine you or your child got earlier isn’t available.
• You don’t know which vaccine you or your child received.
• You or your child started a vaccine series but couldn’t finish it due to side effects.

Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use genetically engineered messenger RNA (mRNA). Coronaviruses have a spikelike structure on their surface called an S protein. COVID-19 mRNA vaccines give your cells instructions for how to make a harmless piece of an S protein.

After vaccination, your muscle cells begin making the S protein pieces and displaying them on cell surfaces. The immune system recognizes the protein and begins building an immune response and making antibodies. After delivering instructions, the mRNA is immediately broken down. It never enters the nucleus of your cells, where your DNA is kept.

The Novavax COVID-19, adjuvanted vaccine is a protein subunit vaccine. These vaccines include only the parts (proteins) of a virus that best stimulate your immune system. The Novavax COVID-19 vaccine contains harmless S proteins. It also has an ingredient called an adjuvant that helps with your immune system response.

Once your immune system recognizes the S proteins, this vaccine creates antibodies and defensive white blood cells. If you later become infected with the COVID-19 virus, the antibodies will fight the virus.

Protein subunit COVID-19 vaccines don’t use any live virus and can’t cause you to become infected with the COVID-19 virus. The protein pieces also don’t enter the nucleus of your cells, where your DNA is kept.

No. The COVID-19 vaccines currently being developed and used in the U.S. don’t use the live virus that causes COVID-19. Because of this, the COVID-19 vaccines can’t cause you to become sick with COVID-19 or shed any vaccine parts.

It can take a few weeks for your body to build immunity after getting a COVID-19 vaccination. As a result, it’s possible that you could become infected with the virus that causes COVID-19 just before or after being vaccinated.

A COVID-19 vaccine can cause mild side effects after the first or second dose, including:

• Pain, redness or swelling where the shot was given.
• Fever.
• Fatigue.
• Headache.
• Muscle pain.
• Chills.
• Joint pain.
• Nausea and vomiting.
• Feeling unwell.
• Swollen lymph nodes.

Babies ages 6 months through 3 years old also might cry, feel sleepy or lose their appetite after vaccination.

A health care team monitors you for 15 minutes after getting a COVID-19 vaccine to see if you have an allergic reaction.

Many people have no side effects from the vaccine. For those who get them, most side effects go away in a few days.

If the redness or tenderness where the shot was given gets worse after 24 hours or you are concerned about any side effects, contact your doctor.

Because COVID-19 vaccines clinical trials only started in the summer of 2020, it’s not yet clear if these vaccines will have long-term side effects. However, vaccines rarely cause long-term side effects.

If you’re concerned, in the U.S., safety data on COVID-19 vaccines will be reported to a national program called the Vaccine Adverse Event Reporting System. This data is available to the public. The CDC has also created v-safe, a smartphone-based tool that allows users to report COVID-19 vaccine side effects.

If you have additional questions or concerns about your symptoms, talk to your doctor.

In some people, COVID-19 vaccines can lead to heart complications called myocarditis and pericarditis. Myocarditis is the swelling, also called inflammation, of the heart muscle. Pericarditis is the swelling, also called inflammation, of the lining outside the heart.

It’s still rare, but in the U.S., there has been an increase in reported cases of myocarditis and pericarditis after mRNA COVID-19 vaccination, particularly in males ages 12 to 39. Research also suggests that there’s a higher risk for these conditions after the Novavax COVID-19 vaccine is given.

Of the cases reported, the problem happened more often after the second dose of the COVID-19 vaccine and typically within one week of COVID-19 vaccination. Most of the people who got care felt better after receiving medicine and resting.

Symptoms to watch for include:

• Chest pain.
• Shortness of breath.
• Feelings of having a fast-beating, fluttering or pounding heart.

If you or your child has any of these symptoms within a week of getting a COVID-19 vaccine, seek medical care.

If you or your child develops myocarditis or pericarditis after a dose of an mRNA COVID-19 vaccine, the CDC recommends avoiding getting another dose of any COVID-19 vaccine.

Yes, COVID-19 vaccines give you protection against serious illness caused by the original strain of the virus and the viruses’ variants that cause COVID-19.

The main variant of the COVID-19 virus in the United States is omicron (B.1.1.529). This variant spreads more easily than the original virus that causes COVID-19 and the delta variant. But omicron seems to cause less severe disease.

Omicron has a few major offshoots, also called sublineages, branching off from B.1.1.529. Together the omicron variants make up nearly all COVID-19 infections in the United States. This is an estimate from early 2023 based on genetic sequencing of samples from people with COVID-19 infections, according to the CDC.

People who are up to date on their vaccines can get breakthrough infections. They can then spread the virus to others. But the COVID-19 vaccines can work to prevent severe illness.

In the U.S., COVID-19 vaccines may be offered at no cost through insurance coverage. For people whose vaccines aren’t covered or for those who don’t have health insurance, options are available. Anyone younger than 18 years old can get no-cost vaccines through the Vaccines for Children program. Adults can get no-cost COVID-19 vaccines through the temporary Bridges to Access program, which is scheduled to end in December 2024.

Yes, COVID-19 vaccines are safe for people who have existing health conditions, including conditions that have a higher risk of getting serious illness with COVID-19.

Your health care team may suggest added doses of COVID-19 vaccine if you have a moderately or severely weakened immune system.

The CDC suggests the shortest time period between the first and second doses of mRNA COVID-19 vaccines for people who have weakened immune systems, people age 65 and older, and others who need rapid protection due to concern about risk of severe illness. An eight-week interval between the first and second doses might be best for some people, especially males ages 12 to 39. A longer interval might increase protection against COVID-19 and reduce the risk of rare heart problems, such as myocarditis and pericarditis.

Don’t take medicine before getting a COVID-19 vaccine to prevent possible discomfort. It’s not clear how these medicines might impact the effectiveness of the vaccines. However, it’s OK to take this kind of medicine after getting a COVID-19 vaccine, as long as you have no other medical reason that would prevent you from taking it.

You might be having an immediate allergic reaction to a COVID-19 vaccine if you experience these symptoms within four hours of getting vaccinated:

• Hives.
• Swelling of the lips, eyes or tongue.
• Wheezing.

If you have any signs of an allergic reaction, get help right away. Tell your doctor about your reaction, even if it went away on its own or you didn’t get emergency care. This reaction might mean you are allergic to the vaccine. You might not be able to get a second dose of the same vaccine. However, you might be able to get a different vaccine for your second dose.

If you have a history of severe allergic reactions not related to vaccines or injectable medicines, you may still get a COVID-19 vaccine. You’re typically monitored for 30 minutes after getting the vaccine.

If you’ve had an immediate allergic reaction to other vaccines or injectable medicines, ask your doctor about getting a COVID-19 vaccine. If you’ve ever had an immediate or severe allergic reaction to any ingredient in a COVID-19 vaccine, the CDC recommends not getting that specific vaccine.

If you have an immediate or severe allergic reaction after getting the first dose of a COVID-19 vaccine, don’t get the second dose. But you might be able to get a different vaccine for your second dose.

If you are pregnant or breastfeeding, the CDC recommends that you get a COVID-19 vaccine.

The overall risk of COVID-19 to pregnant women is low. But women who are pregnant or were recently pregnant are at a higher risk of severe illness with COVID-19. Pregnant women with COVID-19 also are more likely to deliver a baby before the start of the 37th week of pregnancy (premature birth). They also might be at higher risk of problems such as stillbirth and pregnancy loss.

Getting a COVID-19 vaccine can protect you from severe illness due to COVID-19. Vaccination also can help pregnant women build antibodies that might protect their babies. Research shows that infants born to mothers who receive two doses of an mRNA COVID-19 vaccine — such as the Pfizer-BioNTech or Moderna COVID-19 vaccine — might have a lower risk of hospitalization due to COVID-19 infection in their first six months of life.

COVID-19 vaccines don’t cause infection with the virus that causes COVID-19, including in pregnant women or their babies. None of the COVID-19 vaccines contain the live virus that causes COVID-19. Also, keep in mind that mRNA COVID-19 vaccines don’t alter your DNA.

Findings from a study of more than 40,000 women show that getting a COVID-19 vaccine during pregnancy poses no serious risks for pregnant women who were vaccinate