COVID-19: Vaccine Safety and Effectiveness
Why should you get vaccinated?
The COVID-19 vaccines are the best tools to protect yourself and your loved ones from getting sick with COVID-19. There are many reasons to get the COVID-19 vaccine:
- COVID-19 vaccines are safe and effective. Hundreds of millions of people have received COVID-19 vaccines under the most intense safety monitoring in U.S. history.
- Staying up to date with your COVID-19 vaccines can help keep you from getting severely sick, being hospitalized, or dying from the disease.
- Getting vaccinated can help protect people around you since the vaccine helps reduce the spread of COVID-19.
- COVID-19 vaccines offer protection against variants and can help prevent future, possibly more dangerous, variants from developing.
- Vaccination is a safer and more reliable way to build protection than getting sick with COVID-19. COVID-19 vaccination helps protect you by creating an antibody response without you having to experience sickness, potentially including severe illness, or post-COVID conditions. The COVID-19 vaccines do not cause you to become sick with COVID-19 or test positive on a viral test (PCR or antigen).
- COVID-19 vaccines can offer added protection to people who had COVID-19, including protection against being hospitalized from a new infection.
In summary, by receiving all the COVID-19 vaccine doses that are recommended, you can feel safer and know that you have done all you can to protect your health and the lives of the people around you.
Information on available vaccines
There are currently four COVID-19 vaccine brands available in the United States: Pfizer-BioNTech (also called Comirnaty for some ages), Moderna (also called Spikevax for some ages), Johnson & Johnson (Janssen), and Novavax.
Here’s what’s important to know:
- Everyone 6 months and older in the United States is recommended to get an updated COVID-19 vaccine for the best protection.
- In most situations, Pfizer-BioNTech, Moderna, or Novavax COVID-19 vaccines are recommended over Johnson & Johnson's COVID-19 vaccine.
- All COVID-19 vaccines are effective in preventing serious outcomes of COVID-19, including severe disease, hospitalization, and death.
See recent data on COVID-19 vaccine effectiveness
Pfizer-BioNTech COVID-19 vaccines are authorized for individuals 6 months and older. Pfizer (Comirnaty) is fully approved for individuals 12 years and older. Once vaccines are approved by the FDA, companies can market the vaccines under brand names. Comirnaty is the brand name for the Pfizer COVID-19 vaccine for individuals ages 12 years and older. No change has been made to the vaccine’s formula with the name change.
Type: mRNA. This COVID-19 vaccine delivers instructions (using mRNA) so our bodies can make spike proteins. The immune system creates antibodies to attack the spike proteins and learns how to fight COVID-19.
Safety: Side effects throughout the body (such as fever, chills, tiredness, and headache) are more common after the second dose of the vaccine. These are a normal sign that the immune system is learning to fight the virus. Rare cases of myocarditis and pericarditis in adolescents and young adults have been reported after receipt of the Pfizer COVID-19 vaccine. Most patients with myocarditis or pericarditis who received care responded well to medicine and rest and felt better quickly.
How well the vaccine works: Clinical trials and recent vaccine effectiveness studies show that being up to date with Pfizer COVID-19 vaccines provides strong protection against severe disease, hospitalization, and death in all age groups.
- Children 6 months–5 years: In clinical trials, the Pfizer vaccine was 80% effective at preventing symptomatic, laboratory-confirmed COVID-19 in children 6 months–4 years with or without evidence of previous SARS-CoV-2 infection. Children 6–23 months and 2–5 years who received three doses of the Pfizer vaccine had an immune response (measured with antibodies) that was at least as strong as the immune response in people 16–25 years who received two doses of the Pfizer vaccine.
- Children 5–11 years: In clinical trials, the Pfizer-BioNTech vaccine was more than 90% effective at preventing laboratory-confirmed COVID-19 infection in children 5–11 years. The immune response in children 5–11 years was as strong as the immune response in people 16–25 years.
- Children 12–15 years: In clinical trials, the Pfizer-BioNTech vaccine was approximately 100% effective at preventing laboratory-confirmed COVID-19 infection in children 12–15 years. The immune response in children 12–15 years was at least as strong as or stronger than the immune response in people 16–25 years.
- People 16 years and older: In clinical trials, the Pfizer-BioNTech (Comirnaty) vaccine was 95% effective at preventing laboratory-confirmed COVID-19 illness in people 16 years and older who got two doses and had not been previously infected.
Moderna COVID-19 vaccines are authorized for individuals 6 months and older. Moderna (Spikevax) is fully approved for individuals 18 years and older. Once vaccines are approved by the FDA, companies can market the vaccines under brand names. Spikevax is the brand name for the Moderna COVID-19 vaccine for individuals ages 18 years and older. No change has been made to the vaccine’s formula with the name change.
Type: mRNA. This COVID-19 vaccine delivers instructions (using mRNA) so our bodies can make spike proteins. The immune system creates antibodies to attack the spike proteins and learns how to fight COVID-19.
Safety: Side effects throughout the body (such as fever, chills, tiredness, and headache) are more common after the second dose of the vaccine. These are a normal sign that the immune system is learning to fight the virus. Rare cases of myocarditis and pericarditis in adolescents and young adults have been reported after receipt of the Moderna COVID-19 vaccine. Most patients with myocarditis or pericarditis who received care responded well to medicine and rest and felt better quickly.
How well the vaccine works: Clinical trials and recent vaccine effectiveness studies show that being up to date with Moderna COVID-19 vaccines provides strong protection against severe disease, hospitalization, and death in all age groups.
- Children 6 months–5 years: In clinical trials, the Moderna vaccine was around 37.8% effective at preventing symptomatic, laboratory-confirmed COVID-19 in children 6 months–5 years with or without evidence of previous SARS-CoV-2 infection. Children 6–23 months and 2–5 years who received the Moderna vaccine had an immune response (measured with antibodies) that was at least as strong as the immune response in people 18–25 years.
- Children 6–11 years: In clinical trials when the Delta variant was dominant, the vaccine was estimated to be 76.7% effective against symptomatic COVID-19 for children 6–11. However, this analysis may not be reliable due to the low number of COVID-19 cases that occurred in the approximately 4,000 study participants. The vaccine is effective because children 6–11 years had an immune response (measured with antibodies) that was at least as strong as the immune response in people 18–25 years.
- Children 12–17 years: In clinical trials when the original coronavirus and the Alpha variant were dominant, Moderna's vaccine was estimated to be 93.3% effective against symptomatic disease for adolescents 12–17 years old.
- People 18 years and older: In clinical trials, the Moderna vaccine was 94.1% effective at preventing laboratory-confirmed COVID-19 illness in people who received two doses who had no evidence of being previously infected.
Johnson & Johnson COVID-19 vaccine is authorized for individuals 18 years and older.
Type: Viral vector. This COVID-19 vaccine delivers instructions (using a harmless virus) so our bodies can make spike proteins. The immune system creates antibodies to attack the spike proteins and learns how to fight COVID-19.
Safety: There is an increased risk for getting thrombosis with thrombocytopenia syndrome (TTS) following Johnson & Johnson COVID-19 vaccination. TTS is a serious, but rare, adverse event that causes blood clots with low platelets. Women 18–49 years, especially, should be aware of the rare but increased risk of this adverse event. Tragically, nine of the 54 people with TTS died. TTS death rates are highest among women 30–39 years of age (1.93 death per million doses) and 40–49 years of age (1.8 deaths per million doses). There are other COVID-19 vaccine options available for which this risk has not been seen. CDC recommends people receive Pfizer-BioNTech, Moderna, or Novavax COVID-19 vaccines over Johnson & Johnson’s COVID-19 vaccine. Learn more about the Johnson & Johnson COVID-19 vaccine and TTS.
How well the vaccine works: Clinical trials and vaccine effectiveness studies show that being up to date with COVID-19 vaccines provides protection against severe disease, hospitalization, and death.
- The Johnson & Johnson (Janssen) vaccine was 66.3% effective in clinical trials at preventing laboratory-confirmed COVID-19 illness in people who had no evidence of prior infection two weeks after receiving the vaccine. People had the most protection two weeks after getting vaccinated.
- During Omicron circulation, protection was higher for adults who received three COVID-19 mRNA vaccine doses (Pfizer or Moderna) or a Johnson & Johnson vaccine followed by an mRNA booster dose compared to those who received two Johnson & Johnson vaccine doses.
Note: The Novavax COVID-19 vaccine recently received federal regulatory approval and is the fourth vaccine now available for COVID-19. Doses of the Novavax vaccine are expected to begin arriving in Wisconsin in early to mid August.
Novavax COVID-19 vaccine is authorized for individuals 12 years and older.
Type: Protein subunit. This COVID-19 vaccine contains the spike protein of the coronavirus itself, which cannot cause disease. This vaccine uses an older technology whether the protein is made outside of the human body. It also has an adjuvant, an ingredient used to get a better the immune response. The immune system creates antibodies to attack the spike proteins and learns how to fight COVID-19.
Safety: Side effects throughout the body (such as fever, chills, tiredness, and headache) are possible. These are a normal sign that the immune system is learning to fight the virus. Rare cases of myocarditis and pericarditis (six cases in 40,000 participants) were found in the clinical trials. Most patients with myocarditis or pericarditis who received care responded well to medicine and rest and felt better quickly.
How well the vaccine works: In clinical trials, the vaccine was approximately 90% effective against lab-confirmed, symptomatic infection and 100% against moderate and severe disease.
Vaccine development
Developing new vaccines is a thorough and careful process. Safety is the top priority during all phases of vaccine development, approval, and use.
FDA clinical trials
Before the U.S. Food and Drug Administration (FDA) can approve a vaccine, it must be tested through clinical trials to make sure it is safe and to see how well it prevents illness. COVID-19 vaccines were, and continue to be, tested in large clinical trials, made up of far more participants than is usually required, to make sure they met well-established safety standards. Vaccines are also continually assessed and evaluated for safety with new populations, such as children. The participants of the trials include people of different ages, races, and ethnicities, as well as those with different medical conditions to make sure each vaccine is effective. Learn more about how medical experts ensure vaccines work both in clinical trials and the real world through this overview of the COVID-19 vaccine clinical trial and approval process or the FDA webpage on Vaccine Development 101.
Authorization or approval
During a public health emergency, such as the COVID-19 pandemic, the FDA can authorize safe and effective medical devices, treatments and vaccines more quickly using emergency use authorization (EUA). The main differences between EUA and full approval of COVID-19 vaccines are:
- Scientists review the data at every stage, rather than reviewing everything at the end, which takes longer.
- For full approval, FDA needs to review six months of safety data (rather than two months for EUA) and more detailed manufacturing and chemistry data.
After a vaccine receives EUA, additional data can be submitted and reviewed for full FDA approval. The Pfizer, Moderna, and Johnson & Johnson COVID-19 vaccines met FDA's safety and effectiveness standards and were authorized under EUAs. The FDA has now granted full approval for the Moderna (also called Spikevax) vaccine for people ages 18 years and older and the Pfizer-BioNTech (also called Comirnaty) vaccine for people ages 12 and older. These full approvals are further confirmation that these vaccines are effective and safe.
Learn more by visiting the DHS COVID-19 Vaccine Safety fact sheet, FDA's website about EUAs, or FDA's website on approval process terminology.
Continuous safety monitoring
Several systems continue to track common side effects and rare adverse, sometimes serious, reactions in people who receive any vaccine, including COVID-19 vaccines. The CDC and FDA monitor these systems in real time to make sure safety issues are detected as quickly as possible.
- The Vaccine Adverse Event Reporting System (VAERS) is the national system that collects reports from health care professionals, vaccine manufacturers, and the public on adverse events that happen after vaccination. Reports of adverse events that are unexpected, appear to happen more often than expected, or have unusual patterns are followed up with specific studies. Providers are required to report any adverse events to this system. VAERS has alerted public health experts and the public about the very rare adverse events following COVID-19 vaccination: Thrombosis with thrombocytopenia syndrome (TTS), Guillain-Barré Syndrome (GBS), myocarditis, and pericarditis.
- V-safe is a new smartphone-based tool that makes it easy for people to report any health problems or serious reactions after they get their COVID-19 vaccines. Learn how to register and use v-safe by visiting the CDC’s website.
- Vaccine Safety Data Link is a network of nine integrated health care organizations across the U.S. that conduct active surveillance and research. The system is also used to help determine whether possible side effects identified through VAERS are actually related to vaccination.
Frequently asked questions
See answers to frequently asked questions about COVID-19 vaccines, safety, and efficacy by opening the tabs below.
COVID-19 vaccination is recommended for all people ages 6 months and older, including people who are pregnant, breastfeeding, or trying to get pregnant now or might become pregnant in the future.
Based on current data from the v-safe COVID-19 Vaccine Pregnancy Registry, scientists did not find an increased risk for miscarriage among people who received an mRNA COVID-19 vaccine before 20 weeks of pregnancy. This adds to the growing evidence of the safety of these vaccines. Additionally, previous findings from three safety monitoring systems did not find any safety concerns for pregnant people who were vaccinated late in pregnancy or for their babies.
The American College of Obstetricians and Gynecologists and 21 of the leading organizations representing experts in maternal care and public health professionals also issued a statement urging pregnant individuals to be vaccinated.
The increased risk of severe illness and pregnancy complications related to COVID-19 infection makes vaccination for pregnant people more urgent than ever. CDC and DHS recommend that pregnant people should be vaccinated now against COVID-19 if they have not yet received a COVID-19 vaccine. Learn more on the CDC website.
No safety steps were skipped during the development of COVID-19 vaccines. A number of factors allowed safe and effective COVID-19 vaccines to be available quickly.
- Earlier research on other coronaviruses (SARS and MERS) jump-started the COVID-19 vaccine development process. SARS was first detected in 2002, while MERS was first detected in 2012, and both have been researched ever since.
- Through ground-breaking partnerships between leading medical experts, scientists were able to build on lessons learned from past pandemics (Zika, Ebola, H1N1) to make the COVID-19 vaccines.
- Issuing an EUA allowed the vaccines to get to the public faster but did not skip any safety steps. This shortened process still required clinical trials, robust data on safety and effectiveness, and included more experts reviewing the data than previous vaccines. The FDA has now granted full approval for the Pfizer-BioNTech (Comirnaty) vaccine for people 16 years and older and Moderna (Spikevax) for people 18 years and older.
No. The Pfizer and Moderna COVID-19 vaccines are made with mRNA technology. The Johnson & Johnson vaccine (a viral vector vaccine) and the Novavax (a protein-based vaccine) contain just a part of the virus that causes COVID-19 which does not cause illness in humans. Each of these vaccines cannot infect you with COVID-19. Instead, they teach your body how to fight COVID-19 if you do become exposed. Learn more about How Our Bodies Respond to the COVID-19 Vaccine, P-02941.
Nearly all of the ingredients in COVID-19 vaccines are ingredients found in the foods we eat: fats, sugars, and salts. The Pfizer and Moderna COVID-19 vaccines also contain mRNA, and the Johnson & Johnson vaccine contains a part of the virus that causes COVID-19 but does not cause illness in humans. This is what teaches your body how to respond to COVID-19 if you become exposed. See full lists of ingredients for the Pfizer-BioNTech, Moderna, Johnson & Johnson, and Novavax COVID-19 vaccines
The vaccines do not contain fetal cells, blood products, the live SARS-CoV-2 virus, mercury, egg, latex, pork products, preservatives, or microchips.
Yes. Vaccination is important for people with underlying medical conditions, especially those who are moderately to severely immunocompromised, because they may be at an increased risk of severe illness from COVID-19. Everyone 6 months and older should get a COVID-19 vaccine, as long as they are not allergic to any of the ingredients in the vaccine. See the full list of ingredients in the Pfizer-BioNTech, Moderna, Johnson & Johnson, and Novavax COVID-19 vaccines.
Learn more about vaccine considerations for people with underlying medical conditions to make an informed decision.
Serious adverse reactions are possible, although they are very rare. Systems, like VAERS and v-safe, are in place to monitor for reactions to COVID-19 vaccines.
- Severe allergic reaction, including anaphylaxis: Severe allergic reactions can happen after receiving any vaccination or medication. This is why you may be asked to wait 15 minutes after receiving the COVID-19 vaccine. If any severe allergic reaction occurs, medical staff are available to immediately address and treat the reaction.
- Myocarditis and pericarditis: Myocarditis is inflammation of the heart muscle and pericarditis is inflammation of the outer lining of the heart. Symptoms of both myocarditis and pericarditis include:
- Chest pain
- Shortness of breath
- Feelings of having a fast-beating, fluttering, or pounding heart
Seek medical care if you or your child have any of these symptoms, especially if it’s within a week after COVID-19 vaccination. The CDC is actively monitoring reports of myocarditis and pericarditis after COVID-19 vaccination.
- Thrombosis with thrombocytopenia syndrome (TTS): TTS is a very rare but severe type of blood clotting that has occurred following Johnson & Johnson vaccination. There is a risk of TTS, primarily for women 18–49 years old.
In most situations, Pfizer-BioNTech, Moderna, or Novavax COVID-19 vaccines are recommended over Johnson & Johnson's COVID-19 vaccine.
Data from the Vaccine Adverse Event Reporting System (VAERS) shows there is an increased risk, primarily for women 18–49 years old, of a rare but severe type of blood clotting, Thrombosis with thrombocytopenia syndrome (TTS). Of the 54 people who reported having TTS by December 2, 2021, nine people have died. For more data and information see CDC’s webpage on reported adverse events, the Advisory Committee on Immunization Practices (ACIP) updates on TTS, and/or the benefit/risk analysis of Johnson & Johnson COVID-19 vaccination.
The Johnson & Johnson COVID-19 vaccine remains available and may benefit people who:
- Have a contraindication to mRNA COVID-19 vaccines (such as a severe allergic reaction after a previous dose or to a component of an mRNA COVID-19 vaccine).
- Would otherwise remain unvaccinated for COVID-19 due to limited access to mRNA COVID-19 vaccines.
- Want to receive the Johnson & Johnson COVID-19 vaccine despite the safety concerns identified.
It is much safer to get the vaccine than it is to stay unvaccinated and get infected with COVID-19. People are far more likely to get blood clots after COVID-19 infection than after the vaccine. You can look for vaccine by brand at Vaccines.gov or by calling 211.
If you do receive the Johnson & Johnson vaccine, contact your health care provider immediately if you experience any of the following symptoms within three weeks of receiving your vaccine:
- Shortness of breath
- Chest pain
- Leg swelling
- Persistent abdominal pain
- Severe or persistent headaches
- Blurred vision
- Easy bruising or tiny spots under the skin beyond their injection site
Based on initial evidence all authorized or approved vaccines continue to effectively reduce the risk of severe illness and death from COVID-19 for all of the emerging variants. Some variants are able to get around our immune system’s protections more easily and cause infections. As new variants develop, additional doses of the vaccine, or new vaccines, may be recommended to increase protection.
You can use CDC’s COVID-19 booster tool to learn if and when you can get booster doses to get the best protection.
Additional COVID-19 vaccine resources
Access resources and data about the COVID-19 vaccines, including their development and approval, safety, efficacy and more.
Staying up to date with your vaccines
Being up to date on your COVID-19 vaccines ensures you have the best protection possible against severe illness, hospitalization, and death. Learn what it means to be up to date on your vaccines, including what you can and should do afterwards.
