COVID-19 Vaccine Primary Series
The number of vaccine doses you need depends on which vaccine you receive.
- Two doses of Pfizer-BioNTech vaccine should be given 3 weeks (21 days) apart.
- Two doses of Moderna vaccine should be given 4 weeks (28 days) apart.
- Only one dose of Johnson & Johnson’s Janssen (J&J/Janssen) vaccine should be given.
If you receive a vaccine that requires two doses, you should get your second shot as close to the recommended interval as possible. You should not get the second dose earlier than the recommended interval.
COVID-19 vaccines are not interchangeable for your COVID-19 vaccine primary series. If you received a Pfizer-BioNTech or Moderna COVID-19 vaccine for your first shot, you should get the same product for your second shot.
Additional Primary Dose If You Are Immunocompromised
If you received a Pfizer-BioNTech (ages 12 and older) or Moderna (ages 18 and older) mRNA COVID-19 vaccine primary series and have a moderately or severely compromised immune system, you should receive an additional primary dose of the same mRNA COVID-19 vaccine at least 28 days after the second dose.
Additional primary doses are not interchangeable. The vaccine used for the additional primary dose should be the same as the vaccine used for the primary vaccine series. If the mRNA vaccine product given for the first two doses is not available or is unknown, either mRNA COVID-19 vaccine product may be administered.
Currently, CDC does not recommend an additional primary dose if you received a single-dose J&J/Janssen COVID-19 vaccine or in children less than 12 years old with moderate or severely compromised immune systems.
Everyone ages 16 years and older can get a booster shot after they have completed their COVID-19 vaccine primary series. People ages 16 to 17 years old can get the Pfizer-BioNTech COVID-19 booster shot.
People ages 18 years and older have the option to either get the same COVID-19 vaccine product as their primary series, or to get a different COVID-19 vaccine. People may have a preference for the vaccine type that they originally received, or they may prefer to get a different booster. CDC’s recommendations now allow for this type of mix and match dosing for booster shots (Pfizer-BioNTech, Moderna, or J&J/Janssen) for people ages 18 years and older. You may consider the benefits and risks of each product and discuss with your healthcare provider which COVID-19 vaccine product is the most appropriate booster for you.
Currently, a booster shot is not recommended for children younger than 16 years old.