Covid-19: Booster and Additional Doses

Booster doses and additional doses serve different purposes for different groups of people.

An additional dose is recommended for people who are moderately to severely immunocompromised, because they may not have built enough, or any, protection after the initial series.

In contrast, a booster dose helps boost immune systems for better, longer lasting protection after the strong, initial protection decreases over time.

Booster Dose Flyer

Booster Doses

A “booster dose” is a supplemental vaccine dose given to people when the immune response to a primary vaccine series is likely to have decreased over time. While the primary COVID-19 vaccination series continues to be effective at reducing severe disease, hospitalization, and death caused by COVID-19, experts are starting to see that protection against mild to moderate disease can fade over time. The booster dose is intended to boost your immune system for better, long lasting protection. 

Safety data from other countries and the Centers for Disease Control and Prevention (CDC) shows that booster and additional doses are safe. Side effects, which are expected with vaccination, are mostly mild, moderate, and lasted only a few days, similar to the last dose of the primary series. For Pfizer and Moderna vaccines, side effects were reported less frequently following a booster dose than the second dose of the primary series.

Who can get a booster dose?

Everyone ages 12 and older is recommended to get a booster dose for the best protection against COVID-19 and circulating variants. Booster doses are strongly recommended for people who are at the greatest risk for severe disease, such as people who live in long-term care settings and everyone 50 years and older.

If you are eligible, you can get your COVID-19 booster dose:

  • At least 5 months after you got your last dose of your Pfizer or Moderna primary vaccine series.
  • At least 2 months after you got your Johnson & Johnson COVID-19 vaccine.

If you are 18 years or older, you can choose which vaccine you get as a booster dose, no matter which vaccine you got in your primary series. CDC recommends people receive an mRNA COVID-19 vaccine (like Pfizer or Moderna) over Johnson & Johnson’s COVID-19 vaccine. At this time, 12 through 17-year-olds are only allowed to receive a Pfizer vaccine booster dose.

Additional Doses

An “additional dose” is recommended for people who may not have received adequate protection from their initial vaccine series. On August 13, the FDA updated the emergency use authorizations (EUAs) for the Pfizer and Moderna COVID-19 vaccines to allow for additional doses to very specific groups of people. Eligible people can get an additional mRNA dose at any time, as long as it is at least 28 days after completing the initial two-dose mRNA COVID-19 vaccine series (such as for Pfizer and Moderna).

Who should get an additional dose?

Individuals with specific medical conditions or receiving medical treatments that cause them to be moderately to severely immunocompromised are recommended to get an additional dose of Pfizer or Moderna COVID-19 vaccine, if they received a Pfizer vaccine (ages 5 and older) or a Moderna vaccine (ages 18 years and older). People who are immunocompromised have a reduced ability to fight disease, a lower immune response to the original vaccine series compared to other fully vaccinated people, and are especially vulnerable to COVID-19 infection. This includes people who have:

  • Been receiving active cancer treatment for tumors or cancers of the blood.
  • Received an organ transplant and are taking medicine to suppress the immune system.
  • Received a stem cell transplant within the last two years or are taking medicine to suppress the immune system.
  • Moderate or severe primary immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome).
  • Advanced or untreated HIV infection.
  • Active treatment with high-dose corticosteroids, alkylating agents, antimetabolites, transplant-related immunosuppressive drugs, cancer chemotherapeutic agents classified as severely immunosuppressive, tumor-necrosis (TNF) blockers, or other drugs that may suppress your immune response.

Even though the additional dose will be important to help prevent COVID-19 hospitalizations and death, immunocompromised people may still have a reduced immune response after getting the additional dose of the mRNA COVID-19 vaccine. This means it is still important for immunocompromised people to continue to follow current prevention measures (like wearing a mask and physical distancing) even after their additional mRNA COVID-19 vaccine dose and plan to get a booster dose 5 months after their primary series.

Children ages 5 though 11 who are moderately or severely immunocompromised should receive an additional primary dose of vaccine 28 days after their second dose to maximize potential benefit from vaccination.

Talk to your health care provider about:

  • Whether you need to get an additional dose.
  • Whether you will need to pause your treatment or medication before or after getting an additional dose of the vaccine.

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