What to Know about Getting a Booster Dose of the COVID-19 Vaccine

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

MSK patients age 18 and over are eligible for a booster dose of the Pfizer-BioNTech vaccine if they received two doses of it at least six months ago.

The US Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) are now recommending that certain people who received two doses of the Pfizer-BioNTech vaccine receive a booster dose in order to provide greater protection against severe illness from COVID-19. 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 for a booster dose?

New guidelines from the FDA and CDC recommend a booster shot to boost the body’s immune response and offer extra protection for several groups of people (if they received two doses of the Pfizer-BioNTech vaccine at least six months ago). These groups include:

  • adults age 65 and older
  • residents of long-term care facilities
  • adults 18-64 with underlying medical conditions
  • adults working in healthcare or other occupations putting them at high risk of contracting COVID-19
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Are all MSK patients eligible for a booster dose?

Because of the CDC and FDA guidelines, we consider our adult patients who are currently in treatment or previously treated for cancer to be eligible for a booster dose if they received two doses of the Pfizer-BioNTech vaccine at least six months ago. This booster dose must be the Pfizer-BioNTech vaccine.

A select group of cancer patients had already been eligible for an additional dose due to their moderately or severely weakened immune systems. These patients can learn more here. Anyone who has already had three doses of the vaccine should not get a fourth dose at this time.

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    If I am now eligible for a booster dose, when should I get it?

    The booster dose should be scheduled at least six months after the second dose.

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    How can I schedule a booster dose?

    Currently, MSK has limited capacity to administer the Pfizer-BioNTech vaccines. As more becomes available, we will be emailing our patients in phases with information on how to schedule an appointment online.

    In the meantime, we encourage all eligible patients to look for a vaccination location with availability near you, using the following links:

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    If I’ve already been fully vaccinated against COVID-19, why is a booster shot necessary?

    Immune protection tends to weaken over time, and a booster shot can help train the immune system to continue recognizing the virus to protect the body against it. For example, a booster shot of the tetanus and diphtheria vaccine is recommended every 10 years.

    The COVID-19 vaccines are working very well to prevent severe illness, hospitalization, and death, including against the highly contagious Delta variant. However, studies show that some 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 booster shot to enhance their protection.

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    Can I get a booster shot of the Pfizer-BioNTech vaccine if I had previously received Moderna or J&J?

    If you are in the select group of patients whose immune system is moderately or severely weakened and you received two doses of the Moderna vaccine, you may receive an additional dose of Moderna.

    None of the other people who received the Moderna or J&J vaccines are eligible for a booster dose at this time. Moderna submitted to the FDA its application for its booster shot on September 1, 2021, and the federal agency continues to review the data.

    J&J has not yet applied for additional dose clearance. We will share information when the FDA and CDC provide recommendations for either group.

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    What do I need to bring to prove I’m eligible for a booster?

    Please bring your CDC vaccination card or other proof that you have received two doses of the Pfizer-BioNTech vaccine to your vaccine appointment.

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    What side effects should I anticipate if I get a booster dose of the vaccine?

    The side effects from a COVID-19 vaccine booster are similar to the side effects experienced after receiving the first two doses of the vaccine. Scientists in Israel recently began giving an additional dose of the Pfizer-BioNTech vaccine to people with compromised immune systems. Side effects were reported by 31% of people, the most common being soreness at the injection site. Other side effects included fatigue, headache, body aches, and fever. These symptoms don’t last long — about one to three days.

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

    Yes, it is safe to receive the COVID-19 vaccine booster and other vaccines. There does not need to be any interval between the two shots. It is important to protect yourself from both COVID-19 and the flu.


    September 24, 2021


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