Frequently Asked Questions

Is COVID-19 really worse than the flu?

Yes. COVID-19 is more likely to result in severe illness or death than influenza in most age groups, except perhaps young children. Because there is little preexisting immunity to SARS-CoV-2—the virus that causes COVID-19people are also more susceptible to getting sick. Learn more here.

What is herd immunity? How do we get to herd immunity?

Herd immunity occurs when a large portion of a community becomes immune to a disease, making the spread of disease from person to person unlikely. This reduced transmission helps protect the whole community — not just those who are immune. Vaccines are an important tool to help reduce transmission and reach herd immunity with far fewer illnesses and deaths. Learn more here.

What does efficacy mean?

Vaccine efficacy refers to how well a vaccine performs in a clinical trial, under ideal conditions. This is different from effectiveness, which describes how well the vaccine works against the target pathogen in the real world, when it's used in the population. Learn more about efficacy and effectiveness of vaccines here.

Questions about other terminology? Learn more here.

Which COVID-19 vaccine should I get?

All of COVID-19 vaccines available in the U.S. are safe and effective at preventing COVID-19 disease. Get vaccinated as soon as you can, when it's your turn, with whichever vaccine is available. That's how we're going to protect ourselves and our communities, and turn the tide on the pandemic. Learn more about COVID-19 vaccines in Module 2.

(Note from CDC: If you have had a severe allergic reaction (anaphylaxis) or an immediate allergic reaction to any ingredient in the vaccine you are scheduled to receive, you should not get that vaccine. If you have been instructed not to get one type of COVID-19 vaccine, you may still be able to get another type. Learn more information for people with allergies.)

How many doses of COVID-19 vaccine do I need?

The number of doses that you need depends on the vaccine you get, and so does the timing of those doses.

  • For the Johnson & Johnson/Janssen vaccine, you only need 1 dose.

  • For the Pfizer-BioNTech vaccine, you need 2 doses of the vaccine. Your second dose will be given 3 weeks (21 days) after your first dose.

  • For the Moderna vaccine, you need 2 doses. Your second dose will be given 4 weeks (28 days) after your first dose.

You should get your second shot as close to the recommended 3-week or 4-week interval as possible, but not earlier. However, if necessary, your second dose may be given up to 6 weeks (42 days) after the first dose. Learn more here.

Do COVID-19 vaccines hurt? What are the common side effects?

You may have some mild side effects after being vaccinated—these are normal signs that your body is responding to the vaccine and building protection against the SARS-CoV-2 virus. It's common to have a sore arm and some redness and swelling in the arm where you received the vaccine. You may also feel tired and have a fever, chills, or headache. These side effects may affect your ability to do daily activities, but they should go away in a few days. If you registered to participate in CDC's v-safe program, you'll receive a daily text to report these kinds of side effects. Learn more about common side effects.

Who should I contact if I have an adverse event or serious side effect after the vaccine?

If you experience an adverse event after being vaccinated, you can talk to your healthcare provider and report the adverse event to VAERSthe Vaccine Adverse Event Reporting System. You can also talk to your healthcare provider.

Important: If you are experiencing a medical emergency, seek immediate assistance from a healthcare provider or call 9-1-1. CDC and FDA do not provide individual medical treatment, advice, or diagnosis. If you need individual medical or health care advice, consult a qualified healthcare provider.

Learn more about reporting adverse events.

How long does it take after a vaccine for me to develop antibodies?

It typically takes a couple weeks after vaccination for the body to produce the antibodies needed to fight off the target virus. It is possible to become infected with the SARS-CoV-2 virus just before or just after vaccination and then get sick because your body hasn't had enough time to respond to the vaccine and develop antibodies. You are considered "fully vaccinated" 2 weeks after receiving the Johnson & Johnson/Janssen vaccine or 2 weeks after your second dose of the Pfizer-BioNTech or Moderna vaccine. Learn more about how COVID-19 vaccines work in Module 2.

Do I need to wear a mask after I get the COVID-19 vaccine?

Yes. It’s important for everyone to continue using all the tools available to help stop this pandemic as we learn more about how COVID-19 vaccines work in real-world conditions. We are still learning whether getting a COVID-19 vaccine can help prevent you from spreading the virus that causes COVID-19 to other people, even if you don’t get sick yourself. The CDC advises that fully vaccinated people—those who received their final dose of a COVID-19 vaccine at least 2 weeks ago—may:

  • Sit inside a home or private setting without a mask with other fully vaccinated people, and with one household of unvaccinated people, who are not at risk for severe illness

  • Travel without a pre- or post-travel test (depending on the destination) and without quarantining after travel

However, even fully vaccinated people should not visit indoors, without a mask, with people at increased risk for severe COVID-19 illness, nor attend medium or large gatherings.

Learn more about what to do after you are fully vaccinated.

When will I get the COVID-19 vaccine?

Each state has its own plan for rolling out COVID-19 vaccines. You can contact your state health department for more information. As the vaccine supply increases, more groups will be able to access COVID-19 vaccines.

Can I get the vaccine at the same time as I receive other vaccines?

No. You need to wait two weeks after getting the COVID-19 vaccine before getting other immunizations.

Who should not get the COVID-19 vaccine?

People with a severe allergic reaction (anaphylaxis) to any component of the COVID-19 vaccine should NOT receive the vaccine.

Can pregnant or breastfeeding women get the vaccine?

A pregnant or breastfeeding person may choose to be vaccinated against COVID-19. The American College of Obstetricians and Gynecologists (ACOG) recommends that the COVID-19 vaccine should not be withheld from pregnant or breastfeeding individuals. Talk to your healthcare provider if you have questions.