Third COVID injection reduces hospitalization by 93% and mortality by 81%

A third injection of Pfizer’s coronavirus vaccine reduces the chances of hospitalization by 93%, severe illness by 92% and mortality by 81%, according to an Israeli-American study published Friday night in the Lancet.

The study, which compared nearly 730,000 people who received the third injection to the same number who were vaccinated with two injections five months or more earlier and did not receive the booster, was conducted by researchers from Clalit Health Services and Harvard University.

The observational study was conducted during the peak of the Delta wave, from July 30, 2021 to September 23, 2021. It is the first study to be peer-reviewed evaluating the effectiveness of a third dose of the Pfizer vaccine against severe outcomes while regulating a variety of variables, including comorbidities and behavioral factors

“These data provide immediate evidence for other countries now deliberating the need for a booster vaccination campaign similar” to Israel, “said Ran Balicer, Clalit’s chief innovation officer.” Each country will have to make its own decision based on of your environment and the schedule of vaccinations that were provided during the last year.

“In Israel, it suggests that in view of its very early vaccination campaign and waning immunity, the decision for an early vaccination campaign was probably correct and saved many lives,” he said.

Israel was the first nation in the world to carry out a mass vaccination campaign using third-party reinforcements. Since more than 3.9 million Israelis have received the booster, the infection rate in the country has dropped markedly. Less than 1% of people tested for the virus test positive and Israel only has about 230 severe cases.

Many countries around the world are now seeing a resurgence of the virus, largely driven by the Delta variant and its descendants. As such, these countries are considering following Israel and running a reinforcement campaign for the entire population.

Members of the Shaare Zedek Hospital team with security equipment as they work in the coronavirus ward of the Shaare Zedek Hospital in Jerusalem on September 23, 2021 (credit: YONATAN SINDEL / FLASH90).

Specifically, the Clalit and Harvard researchers analyzed anonymous data from 728,321 Clalit patients who received a third dose of the vaccine compared to a control group that included 728,321 people who had received only two doses. Participants were matched for demographic, geographic, and health characteristics related to serious illness, as well as other health or behavioral problems.

Because the study was dynamically based on the participants’ daily vaccination status, about 198,000 people switched from the unvaccinated group to the vaccinated group during the study period.

The study also included another layer of population-level analysis, which found that in each age group, the coronavirus infection rate decreased around seven to 10 days after the age group became eligible for the third vaccine.

“These results … convincingly demonstrate that the third dose of the vaccine is more effective in preventing severe morbidity and hospitalization from coronavirus in different age groups and subgroups of the population,” added Balicer. “These results are extremely important and provide well-founded and valid information to anyone still hesitating to receive the third dose, in Israel and in other countries around the world.”

Professor Ben Rice, director of the Predictive Medicine Group at Boston Children’s Hospital and Harvard Medical School, who also worked on the study, said that “one of the main reasons for hesitation in deciding to get vaccinated with the third dose of the vaccine has been lack of information on the efficacy of the vaccine.

“This rigorous epidemiological study provides reliable information on the effectiveness of the third dose vaccine,” he continued. “We hope it helps those who have not yet decided to get a third dose vaccine.”

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