Information About Boosters and Additional Doses

COVID-19 vaccines are working very well to prevent severe illness, hospitalization, and death, even against the widely circulating Delta variant. However, public health experts are starting to see reduced protection against mild and moderate disease and the Centers for Disease Control and Prevention (CDC) has recommended booster doses for certain groups and has authorized boosters six months after completion of the primary series for recipients of Pfizer or Moderna and two months after receipt of Johnson & Johnson.

Medical studies have suggested that individuals whose immune systems are compromised may have had a reduced antibody response after the usual two-dose vaccine primary series. The U.S. Food and Drug Administration (FDA) recently expanded the Emergency Use Authorizations (EUAs) for the Pfizer and Moderna vaccines to allow for the administration of an additional dose of these vaccines to those who are moderately to severely immunocompromised.

What’s the difference between an additional dose and a booster?

An additional dose is recommended for people who do not have an adequate response to their original vaccine series due to conditions or medications that suppress their immune system. Getting an additional dose can help these individuals make more antibodies and protect against COVID-19.

A booster refers to another dose of a vaccine that is given to someone who built enough protection after vaccination, but then that protection decreased over time (this is called waning immunity).

So far, reactions reported after the additional dose or booster were similar to that of the two-dose series: fatigue and pain at injection site were the most commonly reported side effects, and overall, most symptoms were mild to moderate. However, as with the two-dose series, serious side effects are rare, but may occur.

Who is eligible for a booster dose of COVID-19 vaccines?

The CDC has recommended booster doses of the Pfizer, Moderna and Johnson & Johnson vaccines in certain populations to increase protection against infection with COVID-19. 

Individuals who initially received the Pfizer or Moderna vaccines are eligible for a booster shot if they are:

Individuals who initially received the J&J vaccine are eligible for a booster shot if they are:

  • two months or more from their initial vaccination and
  • 18 years of age or older.

In its recommendations, the CDC has emphasized the particular importance of boosters in people 65 years of age and older, and those who are age 50-64 with underlying medical conditions, because they are more likely to show waning immunity and become seriously ill if they contract COVID-19. 

More information:

  • You will be asked to attest that you meet criteria for a booster dose and recommended to receive the vaccine from the same manufacturer.  The CDC has stated that mixing vaccines is not preferred but is permitted and will be an option for scheduling.

  • The CDC confirmed that it continues to consider individuals to be “fully vaccinated” two weeks after receiving two doses of the Pfizer or Moderna vaccines or one dose of the J&J vaccine. 

Who is eligible for an additional dose of the Pfizer or Moderna vaccine?

The FDA amended the EUAs for both the Pfizer and Moderna COVID-19 Vaccines to allow for the use of an additional dose in certain immunocompromised individuals. This is as a result of medical studies suggesting a reduced antibody response after the usual two-dose vaccine primary series.

The CDC now recommends an additional dose for patients who are moderately to severely immunocompromised with the following conditions: 

  • Active cancer treatment for cancers of the blood and for a solid tumor within one year of your initial mRNA COVID-19 vaccine series (including chemotherapy, hormonal therapy, immunotherapy, surgery and/or radiation therapy) 
  • Received an organ transplant and are taking medicine to suppress the immune system 
  • Received a stem cell transplant within the last 2 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 (or were taking at the time of your initial mRNA COVID-19 vaccine series) with immune-suppressing medications, including high-dose corticosteroids (at least 20 mg of prednisone a day), chemotherapy, tumor necrosis factor (TNF) inhibitors, and other biologic agents that suppress the immune response 

More information: 

  • Additional doses must be administered at least 28 days from the last dose of Pfizer (ages 12 and older) or Moderna (ages 18 and older). 
  • The same manufacturer (Pfizer or Moderna) for additional dose is preferred, but mixing is permissible.
  • Patients who received Johnson & Johnson vaccine are not eligible for an additional dose. The CDC is studying this issue and updates will be provided as available.

Self-schedule for an additional dose or booster through the Yale COVID-19 vaccine program

You will be asked to identify and confirm that you have one or more of the qualifying conditions at the time of scheduling. If you have questions about whether you are immunocompromised, please speak to your treating clinician.

If you have questions about the vaccine or need help scheduling your vaccine, please call the Campus COVID Resource Line at 203-432-6604 for assistance.

Updated October 22, 2021