With the spread of the Omicron variant and the rapid increase in the number of confirmed cases, Israel approved the administration of a fourth vaccine dose to people aged over 60 years and at-risk populations, and later expanded to younger populations.
A new study that was published in the New England Journal of Medicine examined the effectiveness of the fourth dose based on data of over one million people aged 60 or older who were eligible for the vaccine, in the period between January 10 and March 2.
The study found that the rate of severe disease among people who received the fourth dose was lower by a factor of about three compared to people who only received three vaccine doses, and that this protection did not wane throughout the study period.
The rate of confirmed infection in those receiving the fourth dose was lower by a factor of about two compared to people who only received three doses, but this protection waned throughout the eight-week study period.
To avoid possible biases related to differences between those who chose to receive the fourth dose and those who did not, the study also compared the rates of severe disease and confirmed infection among people who received the fourth dose when it became effective, to the rates observed in the first week following the vaccine, during which the vaccine is not yet effective. This analysis yielded similar results showing enhanced protection conferred by the fourth dose.
The study was conducted by a team of researchers from the Weizmann Institute of Science, the Israeli Ministry of Health, the Technion, the Hebrew University, and the Gertner Institute at Sheba Medical Center.