Frequently Asked Questions (FAQs)

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As of today, three vaccines for COVID-19 have received Emergency Use Authorization (EUA) from the U.S. Food and Drug Administration (FDA):

Yes, there are some medical considerations to keep in mind when scheduling your appointment for a COVID-19 vaccine. Vaccination will not be administered if any of the following are true, and scheduling your appointment at a later date is recommended:
  • ●You have received another vaccine in the last 14 days (including vaccines such as Hepatitis B, Shingrix, Tetanus, seasonal flu, etc.).
  • ●You have been diagnosed with COVID-19 in the last 10 days.
  • ●You have received an infusion of COVID-19 monoclonal antibodies to treat COVID-19 in the past 90 days.


Each vaccine uses a slightly different approach with the same goal: to generate an immune response in the body against SARS-CoV2, the virus that causes COVID-19. The vaccines produced by Pfizer and Moderna are both mRNA vaccines. The Janssen vaccine (from Johnson & Johnson) is a viral vector vaccine.

The Pfizer and Moderna mRNA vaccines contain a message from the COVID-19 virus that gives our cells instructions for how to make a harmless protein that is unique to the virus.

After our cells make copies of the protein, they destroy the genetic material from the vaccine. The genetic material from the vaccine does not affect our DNA. Our bodies also recognize that the protein should not be there and build immune cells that will remember how to fight the virus that causes COVID-19 if we are exposed in the future. Both vaccines require two shots, with the second shot received 21 to 28 days after the first, depending on the vaccine.

The Janssen (Johnson & Johnson) vaccine creates a similar immune system response but uses an inactivated harmless cold virus (adenovirus 26) to deliver instructions to your immune system for fighting the virus that causes COVID-19. It requires only one shot.



Producing a vaccine against COVID-19 has been the top priority of scientists and governments around the world to help bring an end to the pandemic. Other versions of the coronavirus have been around for a long time, so scientists had a head start with understanding the basics of how they work. Prior work, combined with the coordinated and enormous investment of resources, has meant the development of these vaccines has been accelerated, all while maintaining standards for safety and efficacy. Rather than eliminating steps from traditional vaccine development timelines, steps are proceeding simultaneously, such as scaling up manufacturing while safety and efficacy data are being collected.

Before receiving approval for emergency use, pharmaceutical companies must provide evidence that their vaccines are safe. A team of experts from the FDA and the CDC’s Advisory Committee on Immunization Practices reviewed all available data on the safety and efficacy of the vaccines before recommending them for use.

No, getting the vaccine cannot give you the virus.

Health care professionals and researchers are still learning about COVID-19 and new information is discovered nearly every day that is helpful in the fight against this disease. Because COVID-19 is still a relatively new virus, it is difficult to know exactly how the virus affects the body long-term and how long immunity from natural infection lasts. Therefore, it is also difficult to predict how long a vaccine will provide protection against the virus. As the vaccines are administered and new information is gathered, additional data about how long it will protect against the virus will be made available.

This is not known at this time. Scientists are continuing to collect data about long-term immunity to SARS-CoV2, the virus that causes COVID-19.

Yes. While experts learn more about the protection that COVID-19 vaccines provide under real-life conditions, it will be important for everyone to continue using all the tools available to us to help stop this pandemic, like covering your mouth and nose with a mask, washing hands often, and staying at least 6 feet away from others. Together, COVID-19 vaccination and following CDC’s recommendations for how to protect yourself and others will offer the best protection from getting and spreading COVID-19.

There is still more to learn about the protection that COVID-19 vaccines provide before deciding to change recommendations on steps everyone should take to slow the spread of the virus that causes COVID-19. Other factors, including how many people get vaccinated and how the virus is spreading in communities, will also affect this decision.



Common short-term side effects that have been reported with available COVID-19 vaccines include the following. Each person’s body will respond differently to getting the vaccine. Not everyone will experience side effects. When they do happen, they are the result of the work the body is doing to create the antibodies needed to protect you, and generally last a day to a few days.
  • ●injection site pain
  • ●tiredness
  • ●headache
  • ●muscle pain
  • ●chills
  • ●joint pain
  • ●fever
  • ●injection site swelling
  • ●injection site redness
  • ●nausea
  • ●feeling unwell
  • ●swollen lymph nodes (lymphadenopathy)

Side effects of individual COVID-19 vaccines may vary. You can find more information about what to expect after getting vaccinated on the CDC website: