Mayo Clinic Staff
Key takeaways
An additional primary shot of a COVID-19 vaccine is recommended for people who are vaccinated and might not have had a strong enough immune response. In contrast, a booster dose is recommended for people who are vaccinated and whose immune response weakened over time. Immune response fades naturally over time. It can also happen when the virus that causes COVID-19 changes so the immune system doesn’t recognize it as well. Research suggests that getting a booster dose can decrease your risk of infection and severe illness with COVID-19.
The CDC recommends additional primary shots and booster doses of COVID-19 vaccines in specific instances:
- Additional primary shot. For people age 5 and older, the CDC recommends a third dose of an mRNA COVID-19 vaccine for some people with weakened immune systems, such as those who have had an organ transplant. People with weakened immune systems might not develop enough immunity after vaccination with two doses of an mRNA COVID-19 vaccine or one dose of the Janssen/Johnson & Johnson COVID-19 vaccine. An additional shot using an mRNA COVID-19 vaccine might improve their protection against COVID-19.The CDC now recommends that children ages 5 through 11 who have moderately or severely weakened immune systems should get an additional primary shot of the Pfizer-BioNTech COVID-19 vaccine.The additional primary shot should be given at least four weeks after a second dose of an mRNA COVID-19 vaccine or one dose of the Janssen/Johnson & Johnson COVID-19 vaccine. The additional shot should be the same brand as the other two mRNA COVID-19 vaccine doses that were given. If the brand given isn’t known, either brand of mRNA COVID-19 vaccine can be given as a third dose.
- Booster dose. These recommendations differ by age, what vaccines you have been given and the state of your immune system.Kids ages 5 through 11 can get a Pfizer-BioNTech COVID-19 booster based on the original viral strain, called a monovalent booster, if they have been given both doses of the Pfizer-BioNTech COVID-19 vaccine. They can get the booster if it’s been at least five months since the last shot.People ages 12 to 17 who had all recommended doses of the Moderna, Pfizer-BioNTech, or Novavax COVID-19 vaccines can only get the Pfizer-BioNTech COVID-19 updated, or bivalent, booster. This booster is based on the original virus strain and two Omicron strains. People can get this shot at least two months after their last shot.
People who are ages 18 and older who had one of these COVID-19 vaccines may get either the Pfizer or Moderna mRNA COVID-19 bivalent booster at least two months after their last shot.
If you are age 18 or older, and got the Janssen COVID-19 vaccine, you can get either of the mRNA vaccine bivalent boosters at least two months after your shot.
Pregnant women can also get a COVID-19 booster shot.
- Booster dose for people with weakened immune systems. Kids ages 5 through 11 who have a weakened immune system should get a monovalent Pfizer-BioNTech COVID-19 vaccine booster shot if they have been given both all recommended doses of the Pfizer-BioNTech COVID-19 vaccine and it’s been at least three months since the additional primary shot.People age 12 to 17 who have a weakened immune system and have had all recommended doses of the Moderna, Pfizer-BioNTech or Novavax COVID-19 vaccines can get an updated, or bivalent, booster dose of the Pfizer-BioNTech COVID-19 vaccine. The bivalent booster can be given at least two months after the last shot.People age 18 and older who have a weakened immune system and have had all recommended doses of the these COVID-19 vaccines can get a bivalent booster dose of either of the Pfizer or Moderna mRNA COVID-19 bivalent boosters. The bivalent booster can be given at least two months after the last shot.