A man receives his third dose of COVID19 vaccine at Sheba Medical Center on July 14, 2021 in Ramat Gan, Israel.

Amir Levy | Getty Images

A third dose of Pfizer‘s Covid vaccine six months after a second shot restores protection from infection to 95% in a real-world setting in Israel, according to data submitted by the company to the Food and Drug Administration.

While the effectiveness of the mRNA vaccine wanes over time, a booster shot was shown to elicit an immune response similar to the protection generated after a second dose, Pfizer said in a 52-page presentation released by the agency Wednesday.

Pfizer said data from Israel’s Covid vaccination program administering boosters to the entire population show that a third shot “has a reactogenicity profile similar to that seen after receipt of the second primary series dose and restores high levels of protection against Covid-19 outcomes (back to approximately 95% protection).” The data was collected from July 1 through Aug. 30 when the delta variant was surging throughout the country.

The FDA released the data as the agency faces pressure from the Biden administration to authorize booster shots for the general population as early as next week. But agency staff declined to take a stance on the need for a third shot, citing the lack of verified data in a 23-page report released later Wednesday.

The staff said it’s reviewing other “potentially relevant” studies on waning immunity from Pfizer’s vaccine, but the studies have produced mixed results and some of that data may be more reliable than others. The Israeli data came from an observational study, which doesn’t adhere to the same standards of a formal clinical trial.

“It should be recognized that while observational studies can enable understanding of real-world effectiveness, there are known and unknown biases that can affect their reliability. Due to these biases some studies may be more reliable than others,” the FDA staff wrote in their analysis.

Pfizer’s report is meant to brief the FDA’s Vaccines and Related Biological Products Advisory Committee, which meets Friday to review the request by Pfizer and its coronavirus vaccine partner, BioNTech, to approve Covid booster doses for the general public. The documents published offer a glimpse of the FDA’s view on third shots.

Based on the data, Pfizer said it “is requesting licensure of a booster dose of [the Pfizer vaccine] administered intramuscularly approximately 6 months after dose 2 in individuals greater than 16 years of age.”

The company also included data from a Phase 3 trial of about 300 people aged 19 to 55. One-third of participants were overweight and one-third were obese, according to the documents.

Pfizer and BioNTech are seeking the agency’s OK to distribute booster doses to people 16 and older across the U.S.

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