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.

A COVID-19 vaccine might:

• Protect you from getting COVID-19
• Prevent you from becoming seriously ill, becoming hospitalized or dying due to COVID-19
• Limit the spread of COVID-19

Getting COVID-19 offers 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 six months.

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.

Because there is an urgent need for COVID-19 vaccines and the Food and Drug Administration's (FDA's) vaccine approval process can take years, the FDA first gave emergency use authorization to COVID-19 vaccines based on less data than is typically 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 through 15.

  For people age 12 and older, the Pfizer-BioNTech COVID-19 vaccine 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 three 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. It requires one shot. Due to the risk of a potentially life-threatening blood-clotting problem, the FDA is restricting use of the Janssen/Johnson & Johnson vaccine to certain people age 18 and older. Examples include people who had a severe allergic reaction after getting an mRNA COVID-19 vaccine and people who can’t get an mRNA COVID-19 vaccine due to limited access or personal or religious concerns. If you get this vaccine, be sure to understand the risks and symptoms of the 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.

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 Janssen/Johnson & Johnson COVID-19 vaccine is a vector vaccine. In this type of vaccine, genetic material from the COVID-19 virus is placed in a different kind of weakened live virus, such as an adenovirus. When the weakened virus (viral vector) gets into your cells, it delivers genetic 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.

No. The COVID-19 vaccines currently being developed in the U.S. don't use the live virus that causes COVID-19. As a result, 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

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.

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 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 29. 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 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.

Some people who received the Janssen/Johnson & Johnson COVID-19 vaccine have developed Guillain-Barre syndrome. This is a rare disorder in which your body's immune system attacks your nerves. The chances of this happening are very low.

This disorder is most often reported in men ages 50 to 64. Symptoms most often appeared within 42 days of vaccination. Seek immediate medical care after getting the Janssen/Johnson & Johnson COVID-19 vaccine if you have:

• Weakness or tingling sensations, especially in the legs or arms, that worsen and spread to other body parts
• Difficulty walking
• Difficulty with facial movements, including speaking, chewing or swallowing
• Double vision or inability to move eyes
• Difficulty with bladder control or bowel function

The Janssen/Johnson & Johnson COVID-19 vaccine can cause thrombosis with thrombocytopenia syndrome. This is a blood-clotting problem that can be life-threatening.

As a result, the FDA is restricting use of the Janssen/Johnson & Johnson vaccine to certain people age 18 and older. Examples include people who had a severe allergic reaction after getting an mRNA COVID-19 vaccine and people who can’t get an mRNA COVID-19 vaccine due to limited access or personal or religious concerns. Research suggests there isn't an increased risk of this blood-clotting problem after mRNA COVID-19 vaccination.

Serious side effects of the Janssen/Johnson & Johnson COVID-19 vaccine typically happen 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

This vaccine shouldn't be given to anyone who develops thrombosis with thrombocytopenia after getting the Janssen/Johnson & Johnson COVID-19 vaccine or any other adenovirus vector COVID-19 vaccine.

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, BA.3, BA.1.1 and BA.2.12.1. BA.2 made up about 62% of COVID-19 infections that had genetic sequencing in the U.S. during a week in late April, according to the CDC.

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 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 and a booster shot.

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.

There is no COVID-19 vaccine yet for children under age 5. Clinical trials involving younger children are in progress.

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 medications, 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 medications, 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. However, you might be able to get a different vaccine for your second dose.

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.

If you are trying to get pregnant or might become pregnant in the near future, it's recommended 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.

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 with 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.

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 through 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 age 16 and older. Research has shown that this vaccine is 100% effective in preventing COVID-19 in children ages 12 through 15.
• Age 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.

The Pfizer-BioNTech COVID-19 vaccine for children ages 5 through 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 through 11.

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

A COVID-19 vaccine can prevent your child from getting COVID-19 and spreading it at home and in 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 play dates and participate in sports and other group activities.

For kids 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 kids 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.

You are considered fully vaccinated two weeks after you get a second dose of an mRNA COVID-19 vaccine or two 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're 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 will also 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 three 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 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.

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 primary shots 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 shot using an mRNA COVID-19 vaccine might improve their protection against COVID-19.

  The additional primary shot should be given at least four weeks 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 that 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 or older, have been given both doses of the Pfizer-BioNTech COVID-19 vaccine and it's been at least five months, get a single 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 vaccine boosters 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.