This Is How Protected You Are After a Pfizer Booster, New Study Says

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The long-running debate over whether or not COVID-19 vaccine boosters would be needed finally ended when the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) authorized their use in some people. The decisions came as more studies found that initial doses showed decreasing effectiveness against the virus. Now, new research has shed light on just how protected people who receive a booster shot of the Pfizer vaccine really are.

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The latest study was published in the journal The Lancet on Oct. 29 and conducted in Israel by the Clalit Research Institute in collaboration with Harvard University. In it, researchers analyzed health record data from July 30, 2021, through Sept. 23, 2021, which is when the Delta variant had become the dominant strain in the country. The team then carefully matched 728,321 patients who had received the initial two doses of the Pfizer COVID-19 vaccine at least five months earlier with 728,321 patients who had received a third shot, pairing them based on similarities in risk, health, age, sex, and location to offer an accurate comparison.

Results found that patients who received Pfizer booster shots were at a 93 percent lower risk of being hospitalized, a 92 percent lower risk of severe disease, and an 81 percent lower risk of death from COVID-19 compared to those who had only received their initial two shots. The researchers also noted that the booster's effectiveness was similar for sexes, age groups, and the number of comorbidities that increased health risk.

According to the study's authors, the research provides the most extensive peer-reviewed study of COVID-19 vaccine booster efficacy in a nationwide setting. "These results show convincingly that the third dose of the vaccine is highly effective against severe COVID-19-related outcomes in different age groups and population subgroups, one week after the third dose," Ran Balicer, MD, PhD, senior author of the study and director of the Clalit Research Institute and Chief Innovation Officer for Israeli health service organization Clalit, said in a press release. "These data should facilitate informed policy decision-making."

RELATED: If You Got Pfizer, This Is When Your Protection Plummets, New Research Says.

Researchers pointed out that the study could not determine the effectiveness of boosters against hospitalization or death in younger patients between the ages of 16 and 39 due to the rate being too low in the group. However, it did also find that infection rates for each age group in Israel began to fall seven to 10 days after it became eligible to receive the third dose.

"To date, one of the main drivers of vaccine hesitancy has been a lack of information regarding the effectiveness of the vaccine," said Ben Reis, PhD, director of the Predictive Medicine Group at Harvard Medical School and the Boston Children's Hospital Computational Health Informatics Program, said in the press release. "This careful epidemiological study provides reliable information on third-dose vaccine effectiveness, which we hope will be helpful to those who have not yet decided about vaccination with a third dose."

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The latest study comes nearly two weeks after Pfizer and BioTech released new results from their Phase 3 controlled trial on Oct. 21, which evaluated the efficacy and safety of a 30-microgram booster dose of the Pfizer vaccine in more than 10,000 patients 16 years and older. Results of the trial found that the Pfizer booster increased relative vaccine efficacy to 95.6 percent compared to those who did not receive a booster during a period in which Delta was the dominant strain in the U.S. The researchers noted that this "restored vaccine protection against COVID-19 to the high levels achieved after the second dose."

Results also found that while there were 109 breakthrough cases in the group that had not received boosters, there were only five reported in the boosted group over the course of the study. "These results provide further evidence of the benefits of boosters as we aim to keep people well-protected against this disease," Albert Bourla, PhD, the chairman and chief executive officer of Pfizer, said in a statement.

RELATED: This Is the Only COVID Vaccine That's More Effective Over Time, CDC Says.