A new study by Tel Aviv University (TAU) and Ben Gurion University of the Negev, in collaboration with the Israeli Ministry of Health, has found that a fourth dose of the existing COVID-19 vaccine is effective in protecting the elderly population in long-term care facilities from the Omicron variant.

The research was based on a study of approximately 40,000 elderly Israelis living in institutions supervised by the Ministry of Health’s “Senior Shield” program, a task force launched by Israel’s government to oversee the prevention and control of COVID-19 in the country’s geriatric facilities. According to its results, elderly at-risk individuals vaccinated with the fourth dose of the Pfizer vaccine have a 34 percent reduced risk of contracting the Omicron variant, a 64 to 67 percent reduced risk of requiring hospitalization due to COVID, and a 72 percent reduced risk of death from the virus.

The study was led by Professor Khitam Muhsen and Professor Dani Cohen of TAU’s School of Public Health; Professor Ron Dagan of Ben Gurion University; Professor 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; program staff members Ami Mizrahi, Omri Bodenheimer, and Boris Boltyansky; and Lea Gaon and Zafrira Hillel-Diamant of the Ministry’s Department of Geriatrics. The study was published on June 23 in JAMA Internal Medicine.

When the Omicron wave spread throughout Israel between January and March of this year, there was no registered and available vaccine for that 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.

Professor Muhsen points out that this new study was conducted on a national scale and 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,” Professor Muhsen says. “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.

“This is a groundbreaking and innovative study based on a database of the elderly population in care facilities,” Professor Muhsen adds. “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 vaccine effect,’ and its results can also be applied to other populations, in Israel and around the world.”

“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,” Professor Cohen concludes.