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Experts answer your questions: COVID-19 Vaccine


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This is a hopeful time. At present, there are more than 125 Million people in the U.S. who have been vaccinated against COVID-19. With more and more people getting the vaccine, we can all look forward to a return to a more normal way of life.

To help address your questions about the vaccines that are now available to people, here are some facts from Tufts Medical Center’s Infectious Diseases doctors.

What COVID-19 vaccines are authorized for people in the United States?

Three vaccines have received Emergency Use Authorization (EUA) from the Food and Drug Administration (FDA). Vaccines from Moderna and Pfizer received authorization in December 2020 and a vaccine by Johnson & Johnson (Janssen) became available in late February 2021. All three vaccines are available at Tufts Medical Center’s Vaccine Clinic.

The Johnson & Johnson (Janssen) vaccine requires one dose while Pfizer and Moderna are given in two doses. Pfizer’s vaccine doses are given 21 days apart and Moderna’s vaccine doses are given 28 days apart.

The Pfizer vaccine is authorized for emergency use for those age 12 and older. Moderna’s and Johnson & Johnson (Janssen)'s vaccines are authorized for emergency use in those 18 and older.

Can I choose which vaccine to get? Should I try to get one vaccine over another because of their effectiveness rates or side effects?

All of the vaccines are highly effective in all of the populations studied. You will be able to choose whether you want an mRNA vaccine (Pfizer or Moderna) or the Johnson & Johnson (Janssen) vaccine. If you choose the mRNA vaccine, which one you get will depend on availability on the day you enter our Vaccine Clinic.

Can I get COVID-19 disease from the vaccine? Will I test positive after receiving the vaccine?

No, you cannot develop COVID-19 disease from any of the vaccines nor does the vaccine affect the results of a COVID-19 PCR or antigen test.

The vaccines were developed so quickly. Are we sure they are safe?

The FDA’s review of the vaccines was thorough and rigorous, and no steps were skipped in the process to review the safety of the vaccines. The FDA decided that the vaccines met safety and efficacy standards based on the currently available data from more than 70,000 diverse volunteers, and it was felt the benefits of the vaccines far outweighed the risk of any known side effects.

The FDA and the CDC paused administration of the Johnson & Johnson (Janssen) vaccine in April due to a small number of vaccine recipients experiencing serious blood clots coupled with low platelet counts. After a thorough review, the CDC advised that vaccination with Johnson & Johnson (Janssen) should resume, but with a warning about the risk of this condition occurring, particularly in women between the ages of 18 and 49. No such risks have been seen with the other two vaccines.

Will a COVID-19 vaccine alter my DNA?

No. The genetic material in the COVID-19 vaccines does not change or interact with your DNA in any way. All COVID-19 vaccines work with the body’s natural defenses to safely develop immunity to disease.

I heard there were side effects after people received the vaccine. What do we know about that?

The most commonly reported side effects for all COVID-19 vaccines are soreness at the site of the injection as well as flu-like symptoms, including fatigue, body aches, chills or fevers after the vaccine. For Pfizer and Moderna, side effects were most common after the second dose of the vaccine, and more likely to be experienced by younger people. These symptoms go away within the first few days after receiving the vaccine. The side effects tell us that the body is building protection against the virus.

What about allergic reactions due to the vaccine?

To date, people who have had allergic reactions to the vaccine have all recovered quickly. The risk of allergic reaction is very small and is similar to the risk of allergic reaction associated with all other medications and vaccines.

Do I need to receive a COVID-19 vaccine if I have been previously infected with COVID-19?

Yes. The CDC recommends that even people previously infected with COVID-19 be vaccinated. This is because the immunity from vaccination appears to be more reliable than the immunity from natural infection. You can choose to delay your vaccination until 90 days after your infection, because you can be fairly confident your immunity from the infection will last that long. Please wait until you have been released from isolation from your COVID-19 infection before going to a vaccination site.

If I receive the Pfizer or Moderna vaccine and I test positive for COVID-19 between dose 1 and dose 2, should I
still get dose 2?

Yes, just be sure to delay your vaccination until you are released from isolation, so that you are no longer contagious to others. Please schedule dose two for as soon as possible after your release from isolation and as long as it is at least 21 days after the first dose of Pfizer vaccine or at least 28 days after the first dose of the Moderna vaccine.

Is it safe for me to get a COVID-19 vaccine if I would like to have a baby one day?

Yes. Whether you are trying to become pregnant now or want to get pregnant in the future, there is no evidence that
COVID-19 vaccination causes any problems with pregnancy, including the development of the placenta. In addition, there is
no evidence that fertility problems are a side effect of any vaccine, including COVID-19 vaccines. Like all vaccines, scientists
are studying COVID-19 vaccines carefully for side effects now and will continue to study them for many years.

Can I get the COVID-19 vaccine if I am pregnant?

Yes. Pregnant individuals are at a higher risk of getting severe COVID-19. For this reason, the CDC, Society for Maternal- Fetal Medicine and American College of Obstetricians and Gynecologists strongly recommend that pregnant individuals have access to COVID-19 vaccines. A conversation with your obstetrical doctor or nurse might help you make a decision. For more information about COVID-19 vaccines and pregnancy, go here.

Can I receive the vaccine if I am breastfeeding?

Yes. The CDC and the Society for Maternal-Fetal Medicine report that there is no reason to believe that the vaccine affects the safety of breastmilk. For more information, go here.

Do the vaccines carry the same precaution/allergy statements?

No, the precautions/allergy statements are different for each vaccine. People who have a known allergy to Polyethylene Glycol (PEG) should not receive the Pfizer or Moderna vaccine. People who have a known allergy to polysorbate should not receive the Johnson & Johnson (Janssen) vaccine. If you have had a severe or immediate allergic reaction to a prior dose of the Moderna or Pfizer vaccine, you may be able to receive the Johnson & Johnson (Janssen) vaccine as your second dose or vice versa. It’s important to discuss this with your primary care physician.

Other types of allergy histories, such as an immediate allergic reaction to another vaccine or injectable therapy, or a history of anaphylaxis due to any cause are considered by the CDC to be a precaution. People who have these reactions should receive the vaccines, but should be observed for 30 minutes (rather than 15) after each dose of vaccine.

Allergic reactions (including severe allergic reactions) not related to vaccines or injectable therapies (e.g., allergic reactions to food, pet, venom, environmental or latex allergies. or oral medications including the oral equivalents of injectable medications) are not a contraindication or precaution to vaccination with COVID-19 vaccines. For more information, see CDC Vaccines & Immunizations.

Can I take the vaccine if I already take other oral medications (anti-anxiety/depression/home medications
and antibiotics)?

Yes. There are no known reactions or interactions between oral medications and the vaccines.

Do the vaccines protect against asymptomatic infection and against vaccinated people from spreading the virus?

Yes. Studies show that the vaccines are extremely effective at preventing COVID-19 illness in vaccinated people. The vaccines are also very effective at preventing asymptomatic infection. When vaccinated people do develop infection, the amount of virus carried in their secretions is lower. Overall, this means that vaccines protect not just you but others.

When I get the vaccine, do I need to continue wearing masks, social distancing, etc.?

The CDC issued guidance on May 16, 2021 for people who are fully vaccinated from COVID-19 indicating that it is safe to do pretty much anything without a mask. You are considered fully vaccinated two weeks after receiving your second dose of either the Pfizer or Moderna vaccines, or two weeks after receiving a single dose of the Johnson & Johnson (Janssen) vaccine. State, local and business-specific rules still apply, and you should expect to be wearing a mask in a variety of settings for a while.

While the CDC mask wearing guidance means a lifestyle change for many, it is important to note that this guidance does not apply to health care settings. At Tufts Medical Center, we continue to require our employees, patients and visitors to be screened at the entrance to our hospital and to wear a face mask at all times even if fully vaccinated.

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