Efficacy of a Fourth Dose of Covid-19 mRNA Vaccine against Omicron

A Fourth Dose of mRNA Vaccine in Health Care Workers Health care workers in Israel were given a fourth dose of BNT162b2 or mRNA-1273 vaccine during a period of omicron-variant predominance. Levels of antibodies to SARS-CoV-2 had waned 5 months after a third dose, and the fourth dose boosted antibodies to the maximum level observed after the third dose but no higher. Vaccine efficacy was 31 to 43% against symptomatic disease.

Automated summary

Health care workers in Israel received a fourth dose of mRNA vaccine during the prevalence of the omicron variant. The fourth dose boosted antibody levels but did not surpass the maximum observed after the third dose. The vaccine demonstrated an efficacy of 31 to 43% against symptomatic disease.