Pfizer booster lowers risk for mortality, severe illness from COVID-19 in Israeli studies

Adults aged 50 years or older who received a Pfizer-BioNTech booster at least 5 months after a second dose of the vaccine had a 90% lower COVID-19 mortality rate compared with those who did not receive a booster.

The findings, published in The New England Journal of Medicine, date before the omicron variant was first detected.

The evidence generated in the study “shows significant lifesaving potential from providing the booster,” Ronen Arbel, PhD, a health outcomes researcher at Clalit Health Services in Tel Aviv, Israel, and colleagues wrote.

Arbel and colleagues conducted an observational study in Israel that included 843,208 adults aged 50 years or older. All participants were members of Clalit Health Services and vaccinated with two doses of the Pfizer vaccine. Of those, 90% received the booster during the 54-day study period, from Aug. 6 to Sept. 29. The participants’ mean age was 68.5 years. Common coexisting conditions included hypertension (46%), obesity (33%) and diabetes (29%).

Mortality estimates

Overall, 65 participants in the booster group (0.16 deaths per 100,000 persons per day) and 137 participants in the nonbooster group (2.98 deaths per 100,000 persons per day) died from COVID-19 during the study period (adjusted HR = 0.1; 95% CI, 0.07-0.14), according to Arbel and colleagues. Among a specific subgroup of participants aged 65 years or older, 60 of 470,808 participants in the booster group and 123 of 35,208 participants in the nonbooster group died from COVID-19 (aHR = 0.09; 95% CI, 0.07-0.13). Similarly, among participants aged younger than 65 years, the mortality rate was lower in the booster group vs. the nonbooster group (aHR = 0.13; 95% CI, 0.04-0.4). When Arbel and colleagues stratified for sex, they observed fewer deaths among men and women in the booster group than among those who did not receive the booster.

Infection and severe illness

A separate study published in The New England Journal of Medicine demonstrated lower rates of confirmed infection and severe illness among individuals aged 16 years or older in Israel who received the Pfizer booster. Specifically, Yinon M. Bar-On, MSc, from the Weizmann Institute of Science in Rehovot, Israel, and colleagues observed that the rate of confirmed infection was about 10 times lower in the booster group than in the nonbooster group. The researchers extracted data from more than 4.6 million individuals who received both doses of the Pfizer vaccine at least 5 months earlier. The study captured outcomes from July 30 to Oct. 10.

Overall, the rate of severe illness was 17.9 times lower in the booster group than in the nonbooster group among those aged 60 years or older (95% CI, 15.1-21.2) and 21.7 times lower among those aged 40 to 59 years. Also, the rate of COVID-19-associated death was 14.7 times lower among those aged 60 years or older who received a booster.

“Booster vaccination programs may provide a way to control transmission without costly social distancing measures and quarantines,” Bar-On and colleagues wrote. “Our findings provide evidence for the short-term effectiveness of the booster dose against the currently dominant delta variant in persons aged 16 years or older.”

The study findings were published shortly after Pfizer and BioNTech released new data that showed a booster dose of their vaccine appears to provide improved protection against the rapidly spreading omicron variant. According to a company press release, a lab study showed that participants who received two doses experienced, on average, a more than 25-fold reduction in neutralization titers against omicron compared with the original virus 3 weeks after the second dose. However, sera collected from people 1 month after a third dose neutralized the variant to levels comparable to the wild-type strain after two doses, the companies said, and there were indications that two doses still protect against more serious infections.

References:

Arbel R, et al. N Engl J Med. 2021;doi:10.1056/NEJMoa2115624.

Bar-On YM, et al. N Engl J Med. 2021;doi:10.1056/NEJMoa2115926.

Pfizer. Pfizer and BioNTech provide update on omicron variant. https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-provide-update-omicron-variant. Accessed Dec. 8, 2021.