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The study was led by Prof. Khitam Muhsen and Prof. Dani Cohen of the School of Public Health at Tel Aviv University, Prof. Ron Dagan of Ben Gurion University, Prof. Nimrod Maimon, director of the Internal Medicine Department at Soroka Medical Center and until recently head of the Ministry of Health’s Senior Shield program, as well as program staff members Ami Mizrahi, Omri Bodenheimer, and Boris Boltyansky, in collaboration with Lea Gaon and Zafrira Hillel-Diamant of the Ministry’s Department of Geriatrics. The study was published in the journal JAMA Internal Medicine.

“Our study compared 24,088 residents of Senior Shield facilities who received a fourth dose of the Pfizer vaccine — that is, the second booster shot — with 19,687 residents who were vaccinated with the first three doses four months or more prior to the follow-up, but who chose not to get the second booster,” explains Prof. Muhsen. “These are residents of geriatric institutions, nursing homes and assisted living facilities that are part of the Ministry of Health’s Senior Shield system — a total of about 1,000 institutions across the country. This population is particularly vulnerable to infection, morbidity and mortality from the coronavirus, due to the nature and living conditions of the institutions, the fact that many residents need help with daily activities, and the previous health issues that many of the residents suffer from.”

When the Omicron wave spread throughout Israel between January and March of this year, there was no registered and available vaccine for this particular variant, which underwent significant mutations in the spike protein that allows the virus to attach to and penetrate human cells. Because the existing COVID-19 vaccines target the spike protein, there has been much discussion in Israel and the rest of the world about the effectiveness of existing vaccines against the Omicron variant in general, and in particular with regards to a second booster shot. Israel was the first country to approve the second booster (the fourth dose of the vaccine) for those aged 60 and above. The present study is based on data from the Senior Shield population database, which constituted the first large group to receive the second booster.

Prof. Muhsen points out that this new study was conducted on a national scale, and that it successfully addressed the methodological problems that characterize observational epidemiological studies on the effectiveness of COVID vaccines. “We monitored the infections, hospitalizations and mortality rates in these two groups throughout the Omicron wave, and found that the members of the group that received the fourth vaccine were infected at a rate that was 34 percent less than the control group; were hospitalized for mild-to-moderate illness 64 percent less, and for severe illness 67 percent less than the control group; and had a mortality rate that was 72 percent less than the group vaccinated with only the first three doses. These are significant data, because the Senior Shield population is one of the groups who suffer the most severe morbidity from the coronavirus, at a much higher rate than the general population. We assume that the fourth dose of the vaccine boosted the level of neutralizing antibodies, which conferred cross-protection against the Omicron variant. Our study points to the significant benefit of administering the fourth dose of the vaccine, and confirms that the policy adopted by the State of Israel was the correct one. The decision to vaccinate at-risk populations with the fourth dose was a wise choice that saved a lot of human lives.”

Prof. Muhsen adds: “This is a groundbreaking and innovative study based on a database of the elderly population in care facilities. Previous studies have been conducted in the general population, and therefore also among relatively young populations with an average age of around 72, whereas the average age in our study was 80. Moreover, in general, people who go to be tested or vaccinated against COVID tend to exhibit positive health behaviors, so it is very difficult to compare their morbidity levels to those of unvaccinated people or those who have been vaccinated with three doses. We have no information as to why some of the residents chose not to receive the fourth vaccine dose, but both groups in our study underwent routine and ‘blind’ COVID tests according to uniform Senior Shield protocol, regardless of whether or not they received the vaccine. Therefore, our study was less affected by the ‘healthy vaccinee effect,’ and its results can also be applied to other populations, in Israel and around the world.”

According to Prof. Dani Cohen, “The study indicates that giving booster shots and raising the level of antibodies through a vaccine based on the original COVID-19 strain provides significant protection against the onset of serious illness even after infection with new variants, including those that are very different from the original, such as Omicron.”

Prof. Nimrod Maimon adds that “The task of protecting institutions for people living outside of the home is a very important aspect of the Ministry of Health’s Senior Shield program. The database that the project has built and accumulated about the institutions and their residents has allowed for rapid and effective vaccination campaigns, which have yielded dramatic results in curbing illness from the coronavirus amongst these populations. The impressive results of the program have received widespread international praise, with health authorities from many countries around the world seeking to learn from the Senior Shield program.”

Prof. Ron Dagan concludes that the results presented in the study demonstrate once again the critical role of vaccines and the use of structured and effective systems in curbing waves of severe morbidity and mortality in at-risk populations.

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Materials provided by Tel-Aviv University. Note: Content may be edited for style and length.