COVID-19 vaccines: Get the facts

Vaccines to prevent coronavirus disease 2019 (COVID-19) are perhaps the best hope for ending the pandemic. But as the U.S. Food and Drug Administration (FDA) continues approving or authorizing emergency use of COVID-19 vaccines, you likely have questions. Find out about the benefits of the COVID-19 vaccines, how they work, the possible side effects and the importance of continuing to take infection prevention steps.

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

Getting COVID-19 offers some natural protection or immunity from reinfection with the virus that causes COVID-19. It's estimated that infection with the virus that causes COVID-19 and vaccination both result in a low risk of another infection with a similar variant for at least 6 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, wait 90 days before getting a COVID-19 vaccine.

Currently, several COVID-19 vaccines are in clinical trials. The FDA continues to review the results of these trials before approving or authorizing COVID-19 vaccines for use. But because there is an urgent need for COVID-19 vaccines and the FDA's 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 the COVID-19 virus with symptoms 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. It requires two injections given 21 days apart. The second dose can be given up to six weeks after the first dose, if needed.

  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 injection, given 21 days 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 Moderna COVID-19 vaccine is 94% effective in preventing COVID-19 with symptoms. This vaccine is authorized for people age 18 and older. It requires two injections given 28 days apart. The second dose can be given up to six weeks after the first dose, if needed.
• 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 injection. The FDA and the Centers for Disease Control and Prevention (CDC) have recommended that use of this vaccine continue in the U.S. because the benefits outweigh the risks. If you are given this vaccine, you should be educated about the possible risks and symptoms of a blood clotting problem.

Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use messenger RNA (mRNA). Coronaviruses have a spikelike structure on their surface called an S protein. COVID-19 mRNA vaccines give cells instructions 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 the protein and begin building an immune response and making antibodies.

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 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 components.

Keep in mind that it will 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.

A COVID-19 vaccine may cause side effects similar to signs and symptoms of COVID-19. If you've been exposed to COVID-19 and you develop symptoms more than three days after getting vaccinated or the symptoms last more than two days, self-isolate and get tested.

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 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. One study suggests that the risk of myocarditis in the week after being fully vaccinated with the Pfizer-BioNTech vaccine is about 54 cases per million doses given to males ages 12 to 17.

Of the cases reported, the problem happened more often after the second dose of the COVID-19 vaccine and typically within several days after 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 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.

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.

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 worsens and spreads 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

Use of the Janssen/Johnson & Johnson COVID-19 vaccine might increase the risk of a rare and serious blood clotting disorder. Nearly all of those affected have been women ages 18 to 49, with the disorder happening at a rate of 7 for every 1 million vaccinated women in this age group. For women age 50 and older and men of all ages, the disorder is even more rare.

The FDA and the CDC have recommended that use of the vaccine in the U.S. can continue because the benefits outweigh the risks. (36) Evidence of these blood clots haven’t been reported in the Pfizer-BioNTech or Moderna COVID-19 vaccines.

Serious side effects of the Janssen/Johnson & Johnson COVID-19 vaccine can occur within three 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

Mild to moderate headaches and muscle aches are common in the first three days after vaccination and don't require emergency care.

Currently, the Centers for Disease Control and Prevention 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. (49;50;51) 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). This variant might spread more easily than other variants, including delta. But it’s not yet clear if omicron causes more severe disease. It’s expected that people who are fully vaccinated likely can get breakthrough infections and spread the virus to others. However, the COVID-19 vaccines are expected to be effective at preventing severe illness. This variant also might reduce the effectiveness of some monoclonal antibody treatments.

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, if you have an existing health condition you can get a COVID-19 vaccine — as long as you haven't had an allergic reaction to a first dose of a COVID-19 vaccine or any of its ingredients. But there is limited information about the safety of the COVID-19 vaccines in people who have weakened immune systems or autoimmune conditions.

COVID-19 vaccines also might not fully protect people from COVID-19 who have a weakened immune system that is caused by HIV, certain conditions or medications. It might be necessary to continue taking precautions.

It isn’t recommended that you take an over-the-counter 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 allergic reaction to a COVID-19 vaccine if you experience these signs 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 should be 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 if you should get 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. 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.

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.

While further research is needed, early findings suggests that getting an mRNA COVID-19 vaccine during pregnancy poses no serious risks for pregnant women who were vaccinated or their babies. The findings are based on data from the CDC’s coronavirus vaccine safety monitoring system. Also, keep in mind that mRNA COVID-19 vaccines don't alter your DNA.

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 have concerns, talk to your health care provider about the risks and benefits of getting a COVID-19 vaccine.

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 COVID-19 vaccines cause fertility problems.

A small number of women have reported experiencing temporary menstrual changes after getting a COVID-19 vaccine. A small study has also shown that some women experienced temporary menstrual changes after getting COVID-19. It's not clear if getting COVID-19 or a COVID-19 vaccine causes these changes. Further research is needed.

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

If you become pregnant after getting the first dose of a COVID-19 vaccine that requires two doses, it’s recommended that you get your second shot.

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

• Ages 5 through 11. The U.S. Food and Drug Administration (FDA) has given emergency use authorization to a Pfizer-BioNTech COVID-19 vaccine for this age group. This vaccine involves two injections, 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 injections, given three weeks apart. 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 through 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 injections, given three weeks apart. The second dose can be given up to six weeks after the first dose, if needed. This vaccine is 91% effective in preventing severe illness with COVID-19 in people age 16 and older.

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 Pfizer-BioNTech COVID-19 vaccine for children ages 5 through 11 also contains a different buffer than the vaccine used for older children and adults. This different buffer, which is used in other FDA-approved vaccines, will help keep the vaccine stable in refrigerated temperatures for longer.

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 and spreading the virus that causes COVID-19.

If your child gets COVID-19, a COVID-19 vaccine could prevent him or her from becoming severely ill or experiencing short-term or long-term complications. Children with other health conditions, such as obesity, diabetes and asthma, might be at higher risk of serious illness with COVID-19.

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.

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 2 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 3 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 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. Currently, there is no time limit after vaccination on your fully vaccinated status.

After you are fully vaccinated, you can more safely return to doing activities that you might not have been able to do because of the pandemic. You can also stop wearing a mask or social distancing in any setting, except where required by a rule or law. However, if you are in an area with a high number of new COVID-19 cases in the last week, the CDC recommends wearing a mask indoors in public and outdoors in crowded areas or when you are in close contact with unvaccinated people. If you are fully vaccinated and have a condition or are taking medications that weaken your immune system, you may need to keep wearing a mask.

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. It’s also recommended that you get tested 3 to 5 days after international travel. However, quarantining isn't needed.

If you’ve been fully vaccinated and you’ve had close contact with someone who has the COVID-19 virus, get tested 5 to 7 days afterward. And if you are a resident or employee of a correctional or detention facility or a homeless shelter and are around someone who has COVID-19, you should still get tested even if you don’t have symptoms of COVID-19.

COVID-19 vaccination will protect most people from getting sick with COVID-19.

A small percentage of fully vaccinated people will still get COVID-19 if they are exposed to the virus that causes COVID-19. These are called vaccine breakthrough infections.

People with vaccine breakthrough infections may spread COVID-19 to others. However, it appears that vaccinated people spread COVID-19 for a shorter period than do unvaccinated people.

Vaccination also might make illness less severe. If you are fully vaccinated, the overall risk of hospitalization and death due to COVID-19 is much lower than among unvaccinated people with similar risk factors.

An additional dose of a COVID-19 vaccine is recommended for people who are fully vaccinated and might not have had a strong enough immune response. In contrast, a booster dose is recommended for people who are fully vaccinated and whose immune response weakened over time.

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

• Additional dose. The CDC recommends a third dose 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. An additional dose might improve their protection against COVID-19.

  The third dose should be given at least 28 days after a second dose of an mRNA COVID-19 vaccine. The additional dose 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. If you are age 18 or older, have been given both doses of the Pfizer-BioNTech COVID-19 vaccine or the Moderna COVID-19 vaccine and it’s been at least 6 months, you should get a single booster dose.

  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 2 months, you should get a single booster dose.

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

  You may choose which vaccine you get as a booster dose. You can get a booster dose that is the same brand as your previous shot or shots or choose a different brand.