You may need extra doses if you have a health problem that weakens your immune system. For example:
- You have had or will have an organ or stem cell transplant.
- You have kidney disease and need dialysis.
- You have acquired immunodeficiency syndrome (AIDS).
- You take certain medicines that weaken your immune system.
If you have a weak immune system, you need at least 3 doses of a COVID-19 vaccine. The XBB.1.5 vaccines can start or complete your 3-dose series. A 3-dose series is “off-label use,” and it is supported by vaccine experts.
If you have already had 3 or more doses of a non-XBB.1.5 COVID-19 vaccine, you can get 1 dose of an XBB.1.5 vaccine at least 3 months after your last dose. If you get a dose of an XBB.1.5 vaccine sooner than 6 months after your last dose, it is “off-label use” if:
- You get Moderna XBB.1.5.
- You get Pfizer-BioNTech XBB.1.5 and you are age 5 to 11 years.
Vaccine experts support the 3-month spacing, and research has found no safety concerns.
Studies show that extra doses may give better protection to adolescents and adults with a weak immune system. In babies and children with a weak immune system, extra doses may also give better protection, but research is still happening to learn more.
Research has shown mRNA vaccines provide the best protection for people with a weak immune system. Information from the use of the original mRNA vaccines shows that the Moderna mRNA vaccine may provide better protection than the Pfizer-BioNTech vaccine for people with a weak immune system.
If you are age 12 to 29 years with a weak immune system and have not had 3 doses of a COVID-19 vaccine, the Pfizer-BioNTech XBB.1.5 vaccine is recommended to start or complete your 3-dose series. This is because the risk of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) was shown to be lower after the first and second dose of the original Pfizer-BioNTech mRNA vaccine compared with the original Moderna mRNA vaccine. However, you can choose to have either vaccine.
Both vaccines have a similar lower risk of myocarditis and pericarditis following additional doses that are given after the second dose. Talk to your healthcare provider if you have questions.
If you have had a stem cell transplant or are getting CAR T-cell therapy (a type of cancer treatment), talk to your healthcare provider about when you can get a dose of XBB.1.5 vaccine and how many doses you need.