You should follow the advice of your healthcare provider. Some immunocompromised people may be eligible for an additional dose of COVID-19 vaccine because of their medical condition. The additional dose should be administered at least 28 days after the second mRNA dose or the first Johnson & Johnson dose. An additional dose is not authorized for those who received the Novavax primary series or those who received the 3-dose Pfizer primary series for children 6 months to 4 years. No doctor’s order necessary, but you may be asked to give verbal confirmation of eligibility.
The CDC recommends people 5 and older receive an age-appropriate, updated mRNA booster dose if at least 2 months have passed since their primary series or since their most recent booster dose. Updated boosters of Pfizer-BioNTech and Moderna contain a bivalent formula that both boosts immunity against the original coronavirus strain and also protects against the Omicron variants that now cause most cases.
CDC recommendations for moderately or severely immunocompromised people can be found here.