The only way to accurately compare the effectiveness of medical products, such as vaccines or drugs, is by direct comparison in head-to-head clinical trials, which did not happen for these vaccines. The CDC recommends the Moderna, Novavax and Pfizer-BioNTech COVID-19 vaccines for the primary vaccination series.
For booster vaccination, Pfizer-BioNTech and Moderna have each created an updated booster dose designed to protect against original strains of the virus, as well as Omicron variants that cause most new infections. The CDC recommends people 6 months 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 newer Omicron variants.
For children age 6 months to 4 years who get the Pfizer primary series, the updated bivalent vaccine will be used as the third dose in the series, rather than as a separate booster. Children in this age group who previously received 3 monovalent Pfizer primary series doses are eligible to receive 1 bivalent Pfizer booster dose at least 2 months after completion of the monovalent primary series. The available COVID-19 vaccines help prevent severe illness, hospitalization, and death. CDC continues to recommend everyone 6 months and older get vaccinated against COVID-19.