When the Omicron variant led to a global resurgence of Covid-19, Israel approved a fourth vaccine dose (second-booster) for individuals aged 60 and above who received a first booster dose four or more months earlier.

Now, a study of all 563,465 eligible 60- to 100-year-old members of Clalit Health Services, the largest HMO in israel, shows that mortality due to Covid-19 among participants who received the second-booster was was 78% lower compared with participants who received only one booster dose.

“The main conclusion is that the second booster is lifesaving,” said Ronen Arbel, Health Outcomes Researcher at Clalit Health Services and Sapir College.

A paper about the results is under consideration for publication in a Nature Portfolio journal. Click here to read the preprint — a preliminary version of a manuscript that has not completed peer review. Authors include Arbel as well as personnel from Clalit’s Community Medical Services Division and from Ben-Gurion University.

Meanwhile, an article in the New England Journal of Medicine from Sheba Medical Center assessing the effectiveness and safety of the second booster in healthy young healthcare workers concludes that it is safe but has “only marginal benefits.”

“Along with previous data showing the superiority of a third dose to a second dose, our results suggest that maximal immunogenicity of mRNA vaccines is achieved after three doses and that antibody levels can be restored by a fourth dose. Furthermore, we observed low vaccine efficacy against infections in health care workers, as well as relatively high viral loads suggesting that those who were infected were infectious,” the authors conclude, noting that older and vulnerable populations were not assessed.