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Vaccine Safety

The UFT has compiled some frequently-asked questions about the safety of the available vaccines for COVID-19. For more information about vaccine appointments and other concerns, visit our vaccine information page

Are the vaccines safe? 

Yes. The COVID-19 vaccines have gone through large clinical studies involving tens of thousands of people of various ages, races and ethnicities. The Food and Drug Administration and independent organizations closely reviewed the evidence from those studies before the government gave emergency use authorization.

How many doses need to be taken of the COVID-19 vaccines to be effective?

Both the Pfizer and Moderna vaccines need two shots to be effective. The first shot starts building protection. A second shot 21 to 28 days later, depending on the vaccine, is needed to get the most protection the vaccine has to offer. The Johnson & Johnson vaccine only requires one dose. 

How well do the vaccines work? 

In clinical studies, both the Pfizer and Moderna vaccines were more than 94% effective at protecting participants from COVID-19 once both doses were received. The Johnson & Johnson vaccine was over was 65% effective and provides high protection against serious illness and hospitalization. 

Will a COVID-19 vaccination protect me from getting sick with COVID-19?

Yes. COVID-19 vaccination works by teaching your immune system how to recognize and fight the virus that causes COVID-19, and this protects you from getting sick with COVID-19.

Are there side effects from the COVID-19 vaccines? 

It is normal to experience side effects after the first or second dose of the vaccine, which is also a sign that the body is building immunity. Common side effects include soreness in the arm where you received your immunization, tiredness or a headache. Other side effects from COVID-19 vaccination could include flu-like symptoms and fever, but these should go away in a few days. Learn more about what side effects to expect and get helpful tips on how to reduce pain and discomfort after your vaccination. If you experience any side effects after taking the vaccine, contact your health care provider as soon as possible. 

Can I get COVID-19 from the vaccine? 

No. None of the COVID-19 vaccines contain the live virus that causes COVID-19, so receiving the vaccine cannot make you sick with COVID-19. 

How long will it take the vaccines to work once administered?

It typically takes a few weeks for the body to build immunity after vaccination. It is possible a person could be infected with the virus that causes COVID-19 just before or just after vaccination and still get sick because the vaccine has not had enough time to provide protection. A person is considered to be fully vaccinated two weeks after the last dose of vaccine. 

I had COVID-19 already. Do I need the vaccine?

Since it is possible to get COVID-19 again, you should be vaccinated. The vaccine may also boost the protection your body has already built up. Talk to your health care provider if you have more questions.

I have allergies and am concerned about complications from the vaccine. Should I get immunized right now? 

Your health care provider knows your personal medical history best, so we recommend you speak with your provider before scheduling an appointment. 

Should women who are pregnant or breastfeeding receive the vaccine?

Pregnant and breastfeeding women should consult with their obstetricians and pediatricians about whether to get the vaccine. Until findings are available from clinical trials and additional studies, only limited data are available on the safety of COVID-19 vaccines administered during pregnancy.

How do mRNA vaccines like the Pfizer and Moderna vaccines work? 

Messenger RNA (mRNA) vaccines make proteins from the coronavirus, which can stimulate the immune system. While the immune protection from these vaccines may last for months or perhaps even years, their mRNA does not — it is destroyed by our cells within days.  Learn more about how COVID-19 mRNA vaccines work. ​

Can the vaccine change my genes or DNA?

No, these vaccines do not have any impact on your genes or DNA. Messenger RNA (mRNA) vaccines teach our cells how to make a protein that triggers an immune response. The mRNA from a COVID-19 vaccine never enters the nucleus of the cell, which is where your DNA is kept. This means the mRNA cannot affect or interact with your DNA in any way and breaks down in the body shortly after it is taken up into our cells. 

To learn more about the COVID-19 vaccines, talk to your health care provider, call 311 within New York City, or visit or