Israeli study points to modest 4-dose vaccine protection against OmicronFour-dose efficacy of mRNA vaccines against symptomatic Omicron COVID-19 infection is modest, according to a research letter yesterday in the New England Journal of Medicine that described a small study in Israel.Of 1,050 eligible Israeli healthcare workers, 154 received a fourth dose of Pfizer and 120 received a fourth dose of Moderna.
The researchers selected two age-matched controls from the remaining eligible participants for each person vaccinated.The fourth dose produced a robust immune response and caused no concerning adverse events.
Overall, 25.0% of the volunteers in the control group were infected with Omicron, compared with 18.3% in the Pfizer group and 20.7% in the Moderna group.The researchers reported vaccine efficacy of 30% for Pfizer and 11% for Moderna for any SAR-CoV-2 infection, but neither vaccine achieved statistical significance for this measure.
Vaccine protection against symptomatic COVID-19 was 43% for Pfizer and 31% for Moderna. Omicron accounted for 100% of circulating SARS-CoV-2 in Israel at the time of the study.The authors note, "Our cohort was too small to allow for accurate determination of vaccine efficacy.