Common questions about COVID-19 vaccinations answered

Updated April 1, 2022

Getting a COVID-19 vaccine is an important tool — along with wearing a cloth mask, socially distancing and good hand hygiene — to help stop the ongoing pandemic. As wide-scale vaccination efforts continue, many people have questions about the vaccines. Mayo Clinic's Vaccination and Distribution Workgroup has answered some of the most common questions about COVID-19 vaccines.

Getting a COVID-19 vaccine is an important tool, along with wearing a mask, socially distancing and good hand hygiene, to help stop the ongoing pandemic. As wide-scale vaccination efforts continue, many people have questions about the vaccines. Mayo Clinic's Vaccination and Distribution Workgroup has answered some of the most common questions about COVID-19 vaccines.

What are the benefits of getting a COVID-19 vaccine?

A COVID-19 vaccine might:

• Prevent you from getting COVID-19 or from becoming seriously ill or dying due to COVID-19
• Prevent you from spreading the virus that causes COVID-19 to others
• Add to the number of people in the community who are protected from getting COVID-19 — making it harder for the disease to spread and contributing to herd immunity
• Prevent the virus that causes COVID-19 from spreading and replicating, which allows it to mutate and possibly become more resistant to vaccines

Should I get the COVID-19 vaccine even if I've already had COVID-19?

Getting COVID-19 might offer some natural protection or immunity from reinfection with the virus that causes COVID-19. It’s estimated that getting COVID-19 and COVID-19 vaccination both result in a low risk of another infection with a similar variant for at least 6 months.

But because reinfection is possible and COVID-19 can cause severe medical complications, it’s recommended that people who have already had COVID-19 get a COVID-19 vaccine.

In addition, COVID-19 vaccination might offer better protection than getting sick with COVID-19. A recent study showed that unvaccinated people who already had COVID-19 are more than twice as likely as fully vaccinated people to be reinfected with COVID-19.

Recent research also suggests that people who got COVID-19 in 2020 and then received mRNA vaccines produce very high levels of antibodies that are likely effective against current and, possibly, future variants. Some scientists call this hybrid immunity. Further research is needed.

If you were treated for COVID-19 with monoclonal antibodies or convalescent plasma, there is no need to delay getting a COVID-19 vaccine.

What COVID-19 vaccines have been authorized or approved and how do they work?

Because there is an urgent need for COVID-19 vaccines and the Food and Drug Administration (FDA) vaccine approval process can take months to years, the FDA first gave emergency use authorization to COVID-19 vaccines based on less data than is normally required. The data must show that the vaccines are safe and effective before the FDA can give emergency use authorization or approval.

Vaccines with FDA emergency use authorization or approval include:

Pfizer-BioNTech COVID-19 vaccine

The FDA has approved the Pfizer-BioNTech COVID-19 vaccine, now called Comirnaty, to prevent COVID-19 in people age 16 and older. The FDA approved Comirnaty after data found the vaccine is safe and effective. The Pfizer-BioNTech COVID-19 vaccine is 91% effective in preventing severe illness with COVID-19 in people age 16 and older.

The vaccine is still under an emergency use authorization for children ages 12 through 15. The vaccine is 100% effective in preventing COVID-19 in children ages 12–15. For people age 12 and older, the Pfizer-BioNTech COVID-19 vaccinate involves two shots. The second dose can be given three to eight weeks after the first dose.

The vaccine is now also available under an emergency use authorization for children ages 5 through 11. This vaccine is about 91% effective in preventing COVID-19 in children ages 5 through 11. It requires two shots, given 3 weeks apart. It also contains a lower dose than the Pfizer-BioNTech COVID-19 vaccine used for people age 12 and older.

Moderna COVID-19 vaccine

The FDA has approved the Moderna COVID-19 vaccine, now called Spikevax, to prevent COVID-19 in people age 18 and older. The Moderna COVID-19 vaccine is 94% effective in preventing COVID-19 with symptoms. It requires two shots. The second dose can be given four to eight weeks after the first dose.

Janssen/Johnson & Johnson COVID-19 vaccine

In clinical trials, this vaccine was 66% effective in preventing the COVID-19 virus with symptoms — as of 14 days after vaccination. The vaccine also was 85% effective at preventing severe disease with COVID-19— at least 28 days after vaccination. This vaccine is authorized for people age 18 and older. It requires one shot. If you are given this vaccine, learn about the possible risks and symptoms of a blood clotting problem.

The shortest interval between the first and second doses of mRNA COVID-19 vaccines is still recommended for people who have weakened immune systems, people age 65 and older and others who need rapid protection due to concern about community transmission or risk of severe illness. An eight-week interval between the first and second doses might be best for some people age 12 and older, especially males ages 12 to 39.

The Centers for Disease Control and Prevention (CDC) recommends getting an mRNA COVID-19 vaccine over getting the Janssen/Johnson & Johnson COVID-19 vaccine. But getting any COVID-19 vaccine is better than not getting a COVID-19 vaccine.

How do the COVID-19 vaccines work?

Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use messenger RNA (mRNA). Coronaviruses have a spike-like structure on their surface called an S protein. COVID-19 mRNA vaccines give cells instructions to immune cells for how to make a harmless piece of an S protein. After vaccination, your cells begin making the protein pieces and displaying them on cell surfaces. Your immune system will recognize that the protein and begin building an immune response and making antibodies. After delivering instructions, the mRNA is immediately broken down. It never enters the nucleus of your cell, where your DNA is kept.

The Janssen/Johnson & Johnson COVID-19 vaccine is a vector vaccine. In this type of vaccine, material from the COVID-19 virus is inserted into a different kind of weakened live virus, such as an adenovirus. When the weakened virus (viral vector) gets into your cells, it delivers material from the COVID-19 virus that gives your cells instructions to make copies of the S protein. Once your cells display the S proteins on their surfaces, your immune system responds by creating antibodies and defensive white blood cells. If you become infected with the virus that causes COVID-19, the antibodies will fight the virus.

Viral vector vaccines can't cause you to become infected with the COVID-19 virus or the viral vector virus. Also, the genetic material that's delivered doesn't become part of your DNA.

If I am vaccinated and develop side effects should I get tested?

While many people do not have reactions after vaccination, it is normal if you do. It does not mean you have the COVID-19 infection. If you have a reaction, take some time to rest and allow your body to recover.

These reactions should not keep you from going to work or doing other activities. However, stay home if you have a fever. It is not necessary to have a COVID-19 test or to quarantine.

What are the possible side effects of the COVID-19 vaccine?

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

You’ll be monitored for 15 minutes after getting a COVID-19 vaccine to see if you have an allergic reaction. Most side effects go away in a few days. Side effects after the second dose might be more intense. Many people have no side effects. Side effects of booster shots appear to be similar to side effects experienced after the two-dose or single-dose primary shots.

Can I get a COVID-19 vaccine if I have an existing health condition?

Yes, COVID-19 vaccines are safe for people who have existing health conditions, including conditions that increase the risk of severe illness with COVID-19. People who have a moderately or severely weakened immune system should get an additional primary shot or booster shot.

What are the long-term side effects of the COVID-19 vaccines?

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.

Is it safe to use fever-reducing pain medications like acetaminophen before or after receiving the COVID-19 vaccine?

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

Do the COVID-19 vaccines protect against the COVID-19 variants?

Currently, the CDC has identified two variants of the virus (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19) as variants of concern:

Delta (B.1.617.2)

This variant is nearly twice as contagious as earlier variants and might cause more severe illness. The greatest risk of transmission is among unvaccinated people. People who are fully vaccinated can get vaccine breakthrough infections and spread the virus to others. However, it appears that fully vaccinated people spread COVID-19 for a shorter period than do unvaccinated people. While research suggests that COVID-19 vaccines are slightly less effective against the delta variant, the Pfizer-BioNTech, Moderna and Janssen/Johnson & Johnson COVID-19 vaccines still appear to provide protection against severe COVID-19.

Omicron (B.1.1.529) and BA lineages

The variant B.1.1.529 spreads more easily than the original virus that causes COVID-19 and the delta variant. However, omicron appears to cause less severe disease. People who are fully vaccinated can get breakthrough infections and spread the virus to others. But, the COVID-19 vaccines are effective at preventing severe illness. This variant also reduces the effectiveness of some monoclonal antibody treatments. Omicron has a few major offshoots (sublineages), including BA.1, BA.2 and BA.3. BA.2 made up about 55% of COVID-19 infections that had genetic sequencing in the U.S. during a week in late March, according to the CDC.

What COVID-19 vaccines have been approved for kids?

In the U.S., COVID-19 vaccines are available to children by age group:

Ages 5 through 11

The FDA has given emergency use authorization to a Pfizer-BioNTech COVID-19 vaccine for this age group. This vaccine involves two shots, given three weeks apart. It contains a lower dose than the Pfizer-BioNTech COVID-19 vaccine used for people age 12 and older.

Research shows that this vaccine is about 91% effective in preventing COVID-19 in children ages 5 through 11.

Ages 12–15

The FDA has given emergency use authorization to a Pfizer-BioNTech COVID-19 vaccine for this age group. This vaccine involves two shots. The second dose can be given three to eight weeks after the first dose. It contains the same dose as the Pfizer-BioNTech COVID-19 vaccine for people ages 16 and older. The second dose can be given up to six weeks after the first dose, if needed.
Research has shown that this vaccine is 100% effective in preventing COVID-19 in children ages 12–15.

Ages 16 and older

The FDA has approved a Pfizer-BioNTech COVID-19 vaccine, now called Comirnaty, for this age group. This vaccine involves two shots. The second dose can be given three to eight weeks after the first dose. This vaccine is 91% effective in preventing severe illness with COVID-19 in people age 16 and older.

The shortest interval between the first and second doses of mRNA COVID-19 vaccines is still recommended for people who have weakened immune systems and others who need rapid protection due to concern about community transmission or risk of severe illness. An eight-week interval between the first and second doses might be best for some people age 12 and older, especially males ages 12 to 39.

Is there any difference in the ingredients or dosing of the Pfizer-BioNTech COVID-19 vaccines for younger children, older children or adults?

The Pfizer-BioNTech COVID-19 vaccine for children ages 5–11 contains a lower dose (10 micrograms) than the vaccine used for older children and adults (30 micrograms). Smaller needles are being used to deliver the vaccine to children ages 5–11.

The ingredients and dosing of the Pfizer-BioNTech COVID-19 vaccine are the same for children ages 12–15 and people age 16 and older.

If children don’t frequently experience severe illness with COVID-19, why do they need a COVID-19 vaccine?

A COVID-19 vaccine can prevent your child from getting COVID-19 and spreading it at home and at school.

If your child gets COVID-19, a COVID-19 vaccine could prevent severe illness.

Getting a COVID-19 vaccine can also help keep your child in school and more safely have playdates and participate in sports and other group activities.

How did the FDA determine the safety and effectiveness of the Pfizer-BioNTech COVID-19 vaccines for use in kids?

For kids ages 5–11, 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 kids ages 12–15, 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.

Can pregnant or breastfeeding women get the COVID-19 vaccine?

If you are pregnant or breastfeeding, it's recommended that you get a COVID-19 vaccine.

The overall risk of COVID-19 to pregnant women is low. However, women who are pregnant or were recently pregnant are at increased risk of severe illness with COVID-19. Pregnant women with COVID-19 are also more likely to deliver a baby before the start of the 37th week of pregnancy (premature birth). They might also be at increased 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 can also 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. In addition, vaccines that use the same viral vector as the Janssen/Johnson & Johnson COVID-19 vaccine have been given to pregnant women in each trimester of pregnancy in clinical trials. No harmful effects were found.

Can a COVID-19 vaccine affect fertility or menstruation?

It's recommended that you get a COVID-19 vaccine if you are trying to get pregnant or might become pregnant in the future. There is no evidence that any vaccines, including COVID-19 vaccines, cause fertility problems in men or women.

It's not clear if getting COVID-19 or a COVID-19 vaccine causes changes in menstruation. A new study of about 4,000 people suggests that getting a COVID-19 vaccine is linked to a less than one-day change in menstrual cycle length for each dose.

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

Can COVID-19 vaccines affect the heart?

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 through 17. Myocarditis is the inflammation of the heart muscle, while pericarditis is the inflammation of the lining outside the heart. These reports are rare.

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 received care felt better after receiving medicine and resting.

Symptoms to watch for include:

• Chest pain
• Shortness of breath
• Feelings of having a fluttering or pounding heart

Of 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.

What are the symptoms of a blood clotting reaction to the Janssen/Johnson & Johnson COVID-19 vaccine?

Use of the Janssen/Johnson & Johnson COVID-19 vaccine as a primary dose or booster dose may increase the risk of a rare and serious blood clotting disorder, especially in women ages 30 to 49.

As a result, the CDC recommends getting an mRNA COVID-19 vaccine over getting the Janssen/Johnson & Johnson COVID-19 vaccine. Research suggests there isn't an increased risk of this disorder after mRNA COVID-19 vaccination.

Serious side effects of the Janssen/Johnson & Johnson COVID-19 vaccine can occur within two weeks of vaccination and require emergency care.

Possible symptoms include:

• Shortness of breath
• Persistent stomach pain
• Severe or persistent headaches or blurred vision
• Chest pain
• Leg swelling
• Easy bruising or tiny red spots on the skin beyond the injection site

Should people who have recovered from COVID-19 get vaccinated?

People who've had COVID-19 infection should still get vaccinated because the vaccine might provide them a longer duration of protection than COVID-19 itself would. This is something that we're still learning and, hopefully, we'll know more about over the next few months.

In general, we recommend that people should wait for about 90 days from infection before they get vaccinated. There is no harm if they get vaccinated beforehand. We know that they're fully protected from their own infection for the first three months, so they can wait for a few months before they get the vaccine and let the others get vaccinated.

Can I stop taking safety precautions after getting a COVID-19 vaccine?

You are considered fully vaccinated 2 weeks after you get a second dose of an mRNA COVID-19 vaccine or 2 weeks after you get a single dose of the Janssen/Johnson & Johnson COVID-19 vaccine. You are considered up to date with your vaccines if you have gotten all recommended COVID-19 vaccines, including booster doses, 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 are in an area with a high number of people with COVID-19 in the hospital and new COVID-19 cases, 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 and new COVID-19 cases. Check with your health care provider to see if you should wear a mask when you're in an area with a lower number of new COVID-19 cases and people with COVID-19 in the hospital.

You also will still be required to 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 are traveling in the U.S., you don’t need to get tested before or after your trip or quarantine after you return. If you are traveling outside of the U.S., you don’t need to get tested before you leave the U.S. unless your destination requires it. You still need to show a negative test result or proof that you’ve recovered from COVID-19 in the past 3 months before boarding an international flight to the U.S.

If you’ve gotten all recommended vaccine doses, including boosters and additional primary shots, and you’ve had close contact with someone who has the COVID-19 virus, get tested at least 5 days after the contact happens.

Are COVID-19 vaccine additional doses or boosters recommended?

An additional primary dose of a COVID-19 vaccine is recommended for people who are vaccinated and might not have had a strong enough immune response. In contrast, a booster dose is recommended for people who are vaccinated and whose immune response weakened over time. Research suggests that getting a booster dose can decrease your risk of infection and severe illness with COVID-19.

People who have a moderately or severely weakened immune system should get an additional primary shot and a booster shot.

The CDC recommends additional doses and booster doses of COVID-19 vaccines in specific instances:

Additional primary shot

The CDC recommends an additional primary shot of an mRNA COVID-19 vaccine for some people with weakened immune systems, such as those who have had an organ transplant. People with weakened immune systems might not develop enough immunity after vaccination with two doses of an mRNA COVID-19 vaccine or one dose of the Janssen/Johnson & Johnson COVID-19 vaccine. An additional dose might improve their protection against COVID-19.

The additional primary shot should be given at least four weeks days after a second dose of an mRNA COVID-19 vaccine or one dose of the Janssen/Johnson & Johnson COVID-19 vaccine. The additional primary shot should be the same brand as the other two mRNA COVID-19 vaccine doses you were given. If the brand given isn’t known, either brand of mRNA COVID-19 vaccine can be given as a third dose.

Booster dose

A single booster dose is recommended for people age 12 and older after getting two doses of an mRNA COVID-19 vaccine or one dose of a Janssen/Johnson & Johnson COVID-19 vaccine.

If you are age 12 and older, have been given both doses of the Pfizer-BioNTech COVID-19 vaccine and it’s been at least five months, get a booster dose. Teens ages 12 to 17 should only get the Pfizer-BioNTech COVID-19 vaccine booster. For people age 18 or older, the Pfizer-BioNTech or Moderna COVID-19 vaccines are preferred in most situations.

If you are age 18 or older, have been given both doses of the Moderna COVID-19 vaccine and it's been at least five months, get a single booster dose. The Pfizer-BioNTech or Moderna COVID-19 vaccine boosters are preferred in most situations.

If you are age 18 or older, have been given one dose of the Janssen/Johnson & Johnson COVID-19 vaccine and it's been at least two months, get a single booster dose. The Pfizer-BioNTech or Moderna COVID-19 vaccine boosters are preferred in most situations.

Pregnant women can also get a COVID-19 booster dose.

If you have a weakened immune system, had two doses of an mRNA COVID-19 vaccine and an additional primary shot, and it’s been at least three months since the additional shot, get a single booster dose. An mRNA COVID-19 vaccine is preferred.

If you have a weakened immune system, had one dose of the Janssen/Johnson & Johnson COVID-19 vaccine and an additional primary shot of an mRNA COVID-19 vaccine, and it’s been at least two months since the additional shot, get a single booster dose. An mRNA COVID-19 vaccine is preferred.

Second booster dose

A second booster dose of an mRNA COVID-19 vaccine is recommended for certain people who have a weakened immune system and people age 50 or older. This second booster dose can be given to those eligible four months after a first booster dose of any authorized or approved COVID-19 vaccine.

Were COVID-19 vaccines developed using fetal tissue?

Neither the Pfizer/BioNTech nor Moderna vaccines for COVID-19 contain fetal cells, and fetal cells were not used in their development or production.

In two animal studies, researchers performed laboratory testing of the vaccines using historically harvested fetal cell lines. However, both animal studies were conducted after these vaccines were already in phase 3 clinical trials.

Can I still get COVID-19 after I’m vaccinated?

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 cases. Some people might not experience any symptoms and some people could become sick due to COVID-19.

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.

Should I delay getting COVID-19 vaccine if I’ve received another type of vaccine recently?

Mayo Clinic experts suggest that you consider delaying your vaccination for COVID-19 if you've received another vaccine within the past 14 days. You also should wait a couple of weeks after being vaccinated for COVID-19 to receive a different vaccine, like the flu vaccine.

While there is no reason to believe that one vaccine will interfere with another, when COVID-19 vaccines were being studied, research volunteers did not receive vaccines at the same time or within two to four weeks of being vaccinated for COVID-19. If you have a reaction after being vaccinated, separating vaccinations helps to correctly identify which vaccine may have been responsible.

Should I delay my COVID-19 vaccine if I am scheduled for surgery?

There is no need to postpone being vaccinated for COVID-19 until after your surgery. Any side effects, such as fever, that may occur from being vaccinated for COVID-19 the vaccine would resolve within seven days. Most side effects resolve within three days.

Mayo does not recommend that you schedule your vaccination for COVID-19 within a few days of your surgery, especially the second dose of the Pfizer/BioNTech or Moderna vaccines for COVID-19. About 15% of people will experience a fever after the second dose of these vaccines. For the first dose, less than 1% will experience a fever.

If you check in on the day of surgery and you have a fever, you may need to reschedule your surgery. A fever immediately after surgery raises concerns about a surgical wound infection, so it's ideal if you can allow a week between being vaccinated for COVID-19 and surgery, especially for the second dose.

Mayo Clinic experts have no concerns with the safety or effectiveness of COVID-19 vaccines for those who choose to be vaccinated for COVID-19 despite a recent vaccination.

Information in this post was accurate at the time of its posting. Due to the fluid nature of the COVID-19 pandemic, scientific understanding, along with guidelines and recommendations, may have changed since the original publication date.