COVID-19 Booster Shots: Eligibility, Safety, and More You Should Know

MSK healthcare worker administering a COVID-19 shot to a patient

You should bring your CDC-issued COVID-19 vaccination card(s) to your booster dose appointment.

The US Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) recommend getting a booster dose in order to provide greater protection against severe illness from the disease.

The CDC endorses booster shots of the Pfizer-BioNTech, Moderna, and Johnson & Johnson/Janssen (J & J) COVID-19 vaccines. The CDC also endorses the mix-and-match approach to boosters, saying eligible people can choose whichever vaccine they wish as a booster.

Mini Kamboj, Memorial Sloan Kettering Cancer Center’s Chief Medical Epidemiologist, has answers to your questions about who is eligible and how you can schedule an appointment.

Who is eligible to receive a COVID-19 booster dose?

If you are eligible to receive a COVID-19 booster dose, the FDA and CDC recommend that you get that booster shot as soon as possible.

If I received the Pfizer-BioNTech vaccine, when can I get a booster?

People age 12 through 17 who received the Pfizer vaccine are eligible for a booster dose of Pfizer five months after their second shot of Pfizer. Those 18 or older may receive a booster of Pfizer or J & J or a half-dose of the Moderna vaccine five months after their second shot of Pfizer.

Note: On January 5, 2022, the CDC agreed with the FDA’s updated recommendations regarding booster doses of the Pfizer vaccine for teens ages 12 to 15. The recommendation is based on studies from more than 6,300 teens ages 12 to 15 in Israel who received a booster dose of the vaccine at least five months following completion of the primary two-dose vaccination series.

If I received the Moderna vaccine, when can I get a booster?

People over age 18 who received the Moderna vaccine are eligible for either a half-dose of the Moderna vaccine or a full dose of Pfizer-BioNTech or J & J. They can receive a booster dose five months after their second shot of Moderna.

If I received the Johnson & Johnson/Janssen vaccine, when can I get a booster?

People over age 18 who received the J & J vaccine are eligible for a Pfizer or J & J booster, or half-dose of Moderna booster. These people are eligible for a booster shot two months after receiving the J & J vaccine. Note: In December 2021, the CDC recommended that adults get the Pfizer or Moderna COVID-19 vaccine rather than J & J, following growing concerns about a rare blood clotting disorder – called thrombosis with thrombocytopenia syndrome (TTS) — after getting the J & J vaccine.

If you received both doses of the Moderna or Pfizer vaccine plus a booster shot, or a single dose of the J & J vaccine plus a booster shot, the FDA and CDC do not recommend that you receive any additional COVID-19 vaccine shots.

Those who received a third dose because they are immunocompromised

People over age 18 who have moderate-to-severe immunosuppression qualify to receive an additional dose, usually because of an organ or stem cell transplant, HIV infection, steroid therapy, or certain cancer treatments that impair the body’s ability to fight infections. If you received that additional dose, you also qualify to get a booster dose — which would be your fourth dose — at least five months later (if you first received the Pfizer or Moderna vaccine). If you first received the J & J vaccine, you can get a booster dose at least two months later.

Update on Blood Clotting Risk From the Johnson & Johnson/Janssen COVID-19 Vaccine
Learn more about the safety of the Johnson & Johnson/Janssen vaccine.
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Why is the Moderna booster shot a half-dose? 

According to data submitted to the FDA and CDC by Moderna, a half-dose booster shot of its COVID-19 vaccine effectively strengthens a person’s immunity against COVID-19 and its variants. In addition, Moderna stated that giving patients a 50-microgram booster shot — half the dose of the original two shots — may reduce side effects a person can experience, such as fatigue, headache, body aches, and fever. The FDA and CDC did not approve a 100-microgram booster dose of the Moderna vaccine.

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Is it safe and effective to mix-and-match vaccine brands?

Yes, a different type of vaccine to boost immune response after the initial vaccination is safe and effective. Federal health officials endorsed this approach, especially for situations where the original vaccine may not be available. It is important to remember that the data on this approach is still limited, and health officials did not recommend one vaccine brand over another as a booster.

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When will MSK be offering these additional booster shots?

MSK is offering additional booster shots now. To check your eligibility and to schedule a booster vaccination at MSK, please use this link. If you have questions about the booster shot, please call your MSK doctor’s office.

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Can I get my booster dose outside of MSK?

Yes. Patients don’t need wait to get a booster shot at MSK. We encourage them to look for a vaccination location with availability near you, using the following links:

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I am getting a COVID-19 vaccine booster dose at MSK. What do I need to bring to my appointment?

Please bring your CDC-issued COVID-19 vaccination card(s) to your booster dose appointment. This is important for us to confirm the date of your last dose. We will update your vaccination card with your booster dose information.

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What side effects should I anticipate if I get a COVID-19 booster dose?

The side effects from an additional dose of the COVID-19 vaccine are similar to those experienced after receiving the original vaccines; the most common are soreness at the injection site, fatigue, headache, body aches, and fever. These symptoms don’t last long typically — about one to three days.

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Is it safe for pregnant people to get a booster shot?

Yes, a growing amount of data continues to confirm that COVID-19 vaccines are safe during pregnancy. On Sept. 29, 2021, the CDC issued an “urgent health advisory,” calling on pregnant people to get vaccinated against COVID-19. The American College of Obstetricians and Gynecologists (AGOC) followed suit on Oct. 1, and encouraged pregnant people who received the Pfizer vaccine at least six months ago to get a booster dose.

The organizations made their recommendations after hospitals nationwide saw a sudden uptick in unvaccinated pregnant women becoming severely ill or hospitalized with COVID-19.  People who are pregnant, unvaccinated against COVID-19, and contract the virus are at higher risk of serious complications, including being admitted to the ICU, needing a breathing tube, and even death. They may also be at higher risk of adverse pregnancy outcomes, such as preterm birth and stillbirth.

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If public health experts are recommending a booster dose, does this mean the COVID-19 vaccines aren’t working?

No. Immune protection tends to weaken over time, and a booster dose can help train the immune system to continue recognizing the virus to protect the body against it. For example, an additional dose of the tetanus and diphtheria vaccine is recommended every 10 years.

The COVID-19 vaccines continue to be very effective in preventing severe illness, hospitalization, and death, including against the highly contagious Delta variant. However, studies show fully vaccinated people have begun to experience reduced protection against mild and moderate infection from COVID-19 and its variants, including Delta. For that reason, people who are eligible should get a COVID-19 booster dose to enhance their protection.

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Is it safe to receive a flu shot and a COVID-19 vaccine booster dose at the same time?

Yes, it is safe to receive a booster dose of the COVID-19 vaccine and other vaccines — such as a flu shot — during the same visit. MSK’s medical experts encourage patients to get both — it is important to protect yourself from both COVID-19 and the flu. If you do get a flu shot and a COVID-19 booster dose at the same time, the CDC advises receiving the injections in different arms to avoid soreness.

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What is the difference between a booster dose and a third dose?

A booster dose is given to someone whose immune system has built excellent immunity after receiving the initial vaccine, but then that protection decreased naturally over time (this is called waning immunity).

A third dose of the vaccine is given to people who may not have achieved strong protection when they were first vaccinated. A vaccine works by activating the immune system. In some people with moderately to severely weakened immune systems (immunocompromised), this ability is impaired, so a third dose of a vaccine can help their immune systems build more protection against a disease.

A small group of these patients became eligible for a third dose of the Moderna and Pfizer vaccines based on recommendations from the FDA and the CDC’s independent advisory board.

These patients may receive a third dose as early as 28 days after the second COVID-19 vaccine dose, instead of waiting 6 months for a booster. The third dose is also a full dose of the vaccine for both Pfizer and Moderna.

For a complete list of eligible patients, click here.


January 10, 2022


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