Fourth vaccine dose 62% effective against severe COVID-19 in month after receipt
Retrospective data from Israel showed that in people ages 60 years and older, an additional booster dose of the Pfizer-BioNTech COVID-19 vaccine was 55% effective against symptomatic disease and 68% effective against hospitalization.
A new study provided data on the effectiveness of a fourth dose of the Pfizer-BioNTech COVID-19 vaccine.
To evaluate the effects of a fourth dose, researchers analyzed data from Jan. 3 to Feb. 18 from the largest health care organization in Israel. They matched patients ages 60 years and older who had received a fourth vaccine dose to patients who had only gotten three doses, the most recent dose at least four months earlier. The primary analysis included 182,122 matched pairs. Results were published by the New England Journal of Medicine on April 13.
The fourth dose was estimated to be 45% effective (95% CI, 44% to 47%) against a positive COVID-19 test in days 7 to 30 after receipt. In the same period, it was 55% effective (95% CI, 53% to 58%) against symptomatic disease, 68% effective (95% CI, 59% to 74%) against COVID-19–related hospitalization, 62% effective (95% CI, 50% to 74%) against severe disease, and 74% effective (95% CI, 50% to 90%) against death from COVID-19. In days 7 to 30, the decrease in absolute risk associated with a fourth dose was 180.1 cases per 100,000 persons (95% CI, 142.8 to 211.9) for COVID-19 hospitalization and 68.8 cases per 100,000 persons (95% CI, 48.5 to 91.9) for severe disease.
“The results of our real-world study suggest that a fourth vaccine dose is, at least initially, effective against the omicron variant,” the authors said, adding that “further studies will be needed to determine whether vaccinating less frequently or offering a combination of different Covid-19 vaccines may be a superior long-term strategy.”
An accompanying editorial noted that the FDA and CDC considered the study's findings in their decision making about an additional booster dose for people ages 50 years and older. The editorialist called on public health officials to moderate expectations that the vaccines should provide complete protection against COVID-19 infection, saying “a zero-tolerance strategy for mild or asymptomatic infection, which can be implemented only with frequent booster doses, will continue to mislead the public about what Covid-19 vaccines can and cannot do.”