Fourth Vaccine Reduces Risk of Dying From COVID by 78 Percent, Israeli Study Finds

As omicron's BA.2 variant is fueling a spike in COVID-19 infections, the latest large-scale study by an Israeli HMO suggests that a fourth dose reduces both the risk of infection and severe illness

Yaron Kelner
New studies suggest the fourth vaccine dose significantly reduces COVID fatality rates.
New studies suggest the fourth vaccine dose significantly reduces COVID fatality rates.Credit: Hadas Parush
Yaron Kelner

Separate studies by Israel’s two largest health care providers published Saturday suggest that the fourth vaccine dose significantly reduces the risk of dying from COVID-19 when compared to the protection offered by three doses of the vaccine.

The study by Clalit Health Services, Israel’s largest health maintenance organization, demonstrates a reduced risk of death, while Maccabi Healthcare Services’ study shows that a fourth vaccine reduces both the risk of infection and of severe illness.

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These findings are particularly relevant as omicron's BA.2 variant is fueling a spike in COVID-19 infections throughout Israel and many other countries.

Clalit’s study covered 563,465 people aged 60 to 100 who had received three doses of the vaccine. They were divided into two groups: those who chose to receive a fourth dose, and those who chose not to receive a fourth dose. Of the participants, 58 percent received a fourth vaccine.

The researchers compared the mortality rate in the two populations between January 10, about a week after the approval of the fourth dose, and February 20. During this period 232 people died in the group that received only three doses, compared with 92 in the group that received four.

According to the researchers, the data show that the fourth vaccine reduces the risk of dying from the coronavirus in older adults by 78 percent.

The Clalit study has not yet been peer-reviewed, and is currently in the process of being accepted for publication in a journal. It was carried out by Clalit’s Community Medicine Division in collaboration with the Faculty of Health Sciences at Ben-Gurion University of the Negev and the Maximizing Health Outcomes Research Lab at Sapir Academic College.

The head of the Community Medicine Division, Dr. Doron Netzer, explains that the findings are important because the prevailing perception is that the omicron variant causes only mild illness, so no additional vaccine is needed.

“The results of the study show that the fourth dose is significantly associated with a reduced risk of mortality from coronavirus, including from omicron,” he said.

Maccabi’s study examined the effectiveness of the vaccine for nine weeks, from January to March, among about 100,000 Maccabi members 60 and older who were vaccinated in three doses. It showed that the fourth dose was 73 percent more effective in preventing severe illness than three doses. However, fewer than 1 percent of the participants who were vaccinated with at least three doses experienced severe COVID-19.

The results also showed the efficacy of the fourth dose against infection with the coronavirus. According to the study, about three weeks after receiving the fourth vaccine, the risk of becoming infected decreases by 64 percent compared to those vaccinated with only three doses. However, 10 weeks after the fourth vaccine the reduction in risk drops to 29 percent, indicating that the added protection it offers dissipates more quickly than that provided by the third dose.

The study was conducted by KSM, the Maccabi Research and Innovation Center, and is awaiting peer review.

According to the researchers, more studies are needed over a longer period to determine the duration of protection afforded by the fourth dose over time. They added that more studies could examine how re-exposure to the same vaccine affects protection against different variants.

The fourth dose of vaccine was approved by the Health Ministry on January 2 for people 60 and over as well as health care workers, provided that four months have passed since receiving the third vaccine. The decision, which set a global precedent, was made at the beginning of the omicron wave in Israel, in a bid to increase protection against the variant that broke through the immune defense of many vaccinated people.

Yet despite the high rates of infection and illness, relatively few people have agreed to a fourth dose: about 750,000 people, compared with 6.7 million people in Israel who have received one dose of the coronavirus vaccine, 6.1 million who have had two doses and 4.4 million with three doses.

On Thursday, Prime Minister Naftali Bennett and Health Minister Nitzan Horowitz met with the heads of the country’s four HMOs and offered them a 100 shekel ($31) bonus for each person age 60 and over who receives a fourth dose.

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