COVID-19 vaccines: Get the facts

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.
• Be a safer way to protect yourself compared to getting sick with the virus that causes COVID-19.
• Boost your body's protection, also called immunity, against catching the virus that causes COVID-19.

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.

At the start of the COVID-19 pandemic, there was an urgent need for COVID-19 vaccines. The U.S. Food and Drug Administration's (FDA's) vaccine approval process can take years.

So the FDA first gave emergency use authorization to COVID-19 vaccines based on less data than is typically required. But the data still had to show that the vaccines were safe and effective.

Vaccines with FDA emergency use authorization or approval include:

• Pfizer-BioNTech COVID-19 vaccine. This vaccine was first tested against the original strain of the virus that causes COVID-19, which began spreading at the end of 2019. In December 2020, the Pfizer-BioNTech COVID-19 vaccine 2-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 and older. The number of shots in this vaccination series varies based on a person's age and COVID-19 vaccination history.

• 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. Based on clinical trial data the vaccine effect was predicted for younger people.

  The vaccine is approved under the name Spikevax for people age 18 and older. The vaccine is authorized for use in people age 6 months and older. The number of shots needed varies based on a person's age and COVID-19 vaccination history.

In August 2022, the FDA authorized an update to the Moderna and the Pfizer-BioNTech COVID-19 vaccines. Both now include the original and omicron variants of the virus that causes COVID-19. The updated, called bivalent, vaccines continue to prevent serious illness in those who are up to date with COVID-19 vaccines. In one analysis, they were up to 62% effective at keeping adults with COVID-19 from needing COVID-19 care in the hospital.

• 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.

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., the federal government is providing COVID-19 vaccines free of charge to all residents, regardless of immigration status or health insurance coverage. The COVID-19 vaccines are free whether offered by a clinic, retail pharmacy or other location.

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 vaccinated or their babies. Most of the women in the study received an mRNA vaccine.

If you are trying to get pregnant or might become pregnant in the near future, the CDC recommends that you get a COVID-19 vaccine. There is no evidence that any vaccines, including COVID-19 vaccines, cause fertility problems in men or women.

COVID-19 vaccines might affect menstrual cycles. A new survey of more than 39,000 people between ages 18 and 80 showed that 42% of people with regular menstrual cycles had heavier bleeding than usual after vaccination. In contrast, 44% reported no change and 14% had lighter periods than usual. In addition, 71% of people using long-acting reversible contraceptives, 39% of people using gender-affirming hormones and 66% of post-menopausal people reported breakthrough bleeding. All of the people surveyed were fully vaccinated against COVID-19 and, to their knowledge, hadn't gotten COVID-19 before being vaccinated.

Keep in mind that many things can affect menstrual cycles, including infections, stress, sleep problems, and changes in diet or exercise.

In the U.S., COVID-19 vaccines are available to children based on their age. The number of shots, also called doses, depends on the vaccine and the child's vaccine history.

• Pfizer-BioNTech COVID-19 vaccine. For children between ages 6 months and 4 years, three shots of the vaccine brings them up to date. The three shots may be a mix of the original, called monovalent, vaccine and the currently available vaccine called an updated or bivalent vaccine.

  After the first dose, the second shot is given at least 3 to 8 weeks later. The third shot is given at least 8 weeks after that.

  If a child has had three shots of the monovalent Pfizer-BioNTech COVID-19 vaccine, the child is eligible for one additional dose of the bivalent vaccine at least eight weeks after their last monovalent shot.

  People age 5 years and older who are unvaccinated need one shot to be considered up to date. Those who already had one dose of monovalent vaccine can get a bivalent shot at least eight weeks after the original dose.

  For people age 5 and older who have already had one dose of the bivalent vaccine, the CDC hasn't recommended more shots.

• Moderna COVID-19 vaccine. For children between ages 6 months and 5 years, the series is two doses. After the first dose, the second is given at least 4 to 8 weeks later.

  For kids between ages 6 months and 5 years who previously got two shots of the monovalent Moderna COVID-19 vaccine, an additional dose of the currently available bivalent vaccine is recommended. That shot can be given at least eight weeks after the second monovalent vaccine.

  For people age 6 and older one shot will bring them up to date. For people in this age group who had one shot of the monovalent vaccine, an additional dose of the bivalent vaccine is recommended. This can be given at least eight weeks after the first shot.

• Novavax vaccine. For people age 12 and older the series is two shots of the vaccine. The second shot is recommended 3 to 8 weeks after the first shot. The CDC recommends that people who get a Novavax vaccine series also get one shot of either Moderna or Pfizer-BioNTech COVID-19 bivalent vaccine at least eight weeks after their second Novavax shot.

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 give more protection against COVID-19 and lower the risk of rare heart problems, such as myocarditis and pericarditis. Also, if your child recently had COVID-19, you may talk to a health care professional about delaying vaccination by up to three months.

Yes. The Pfizer-BioNTech COVID-19 vaccine for children ages 6 months to 4 years old and the Moderna COVID-19 vaccine for children ages 6 months through 5 years have lower amounts of mRNA than the Pfizer-BioNTech and Moderna COVID-19 vaccines for people age 12 and older.

While rare, some children can become seriously ill with COVID-19 after getting the virus that causes COVID-19.

A COVID-19 vaccine and booster, updated to the most common strain of the virus that causes COVID-19, might prevent your child from getting the virus that causes COVID-19. It also may prevent your child from becoming seriously ill or having to stay in the hospital due to the COVID-19 virus.

For children ages 5 through 11, the FDA reviewed a vaccine study of more than 4,600 children in this age range. Of this group, about 3,100 were given the Pfizer-BioNTech COVID-19 vaccine. The other children were given an inactive (placebo) shot. Children who were given the vaccine were monitored for side effects for at least two months after the second dose. Side effects were generally mild to moderate.

The FDA also took an early look at cases of COVID-19 that occurred one week after children were given a second dose of the vaccine. None of the children in this analysis had been previously diagnosed with COVID-19. Among 1,305 children given the vaccine, there were three cases of COVID-19. Among 663 children given the placebo, there were 16 cases of COVID-19. The results suggest that the vaccine is about 91% effective in preventing COVID-19 in this age group.

For children ages 12 through 15, the FDA reviewed a vaccine study of more than 2,200 U.S. children in this age range. Of this group, about half were given the Pfizer-BioNTech COVID-19 vaccine. The other children were given a placebo shot. A week after the second dose was given, there were no cases of COVID-19 in the 1,005 children given the Pfizer-BioNTech vaccine.

Among 978 children given the placebo, there were 16 cases of COVID-19. None of the children had previously been diagnosed with COVID-19. The results suggest that the vaccine is 100% effective at preventing the COVID-19 virus in this age group. Also, a portion of the children in each age group were monitored for safety for at least two months after being given the second dose of the COVID-19 vaccine.

To find out the effectiveness of the Pfizer-BioNTech vaccine for children ages 6 months through 4 and the Moderna COVID-19 vaccine for children ages 6 months through 17 years old, the FDA looked at the immune responses of children in these age groups after they were fully vaccinated.

The FDA compared those responses to the immune responses of young adults who'd been given higher doses of the same mRNA vaccine.

As with the other vaccines, side effects were recorded and some of the children were monitored for safety for at least two months after being fully vaccinated.

To find out how well the Novavax COVID-19 vaccine worked, the FDA reviewed data on 2,232 people ages 12 to 17. The research suggests that the vaccine was about 78% effective at preventing COVID-19 disease in this age group.

You are considered up to date with your vaccines if you have gotten all recommended COVID-19 vaccine shots when you become eligible.

After getting vaccinated, you can more safely return to doing activities that you might not have been able to do because of the pandemic. However, if you're in an area with a high number of people with COVID-19 in the hospital, the CDC recommends wearing a well-fitted mask indoors in public, whether or not you're vaccinated.

If you have a weakened immune system or have a higher risk of serious illness, wear a mask that provides you with the most protection possible when you're in an area with a high number of people with COVID-19 in the hospital. Check with your health care provider to see if you should wear a mask at other times.

The CDC recommends that you wear a mask on planes, buses, trains and other public transportation traveling to, within or out of the U.S., as well as in places such as airports and train stations.

If you've gotten all recommended vaccine doses and you've had close contact with someone who has the COVID-19 virus, get tested at least five days after the contact happens.

COVID-19 vaccination will protect most people from getting sick with COVID-19. But some fully vaccinated people will still get COVID-19. These are called vaccine breakthrough infections.

People with vaccine breakthrough infections can spread COVID-19 to others. However, fully vaccinated people with a breakthrough infection are less likely to have serious illness with COVID-19 than those who are unvaccinated. Even when vaccinated people develop symptoms, they tend to be less severe than those experienced by unvaccinated people.

An additional primary shot of a COVID-19 vaccine is recommended for people who are vaccinated and might not have had a strong enough immune response.