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A pharmacist administers a third dose of the Pfizer-BioNTech COVID-19 vaccine to a customer at a pharmacy in Livonia, Mich., on Aug. 17, 2021.
A pharmacist administers a third dose of the Pfizer-BioNTech COVID-19 vaccine to a customer at a pharmacy in Livonia, Mich., on Aug. 17, 2021. (Emily Elconin/Bloomberg)

Pfizer said that data from the U.S. and Israel suggest that the efficacy of its COVID-19 vaccine wanes over time, and that a booster dose was safe and effective at warding off the virus and new variants.

The company detailed the data in a presentation it will deliver to a meeting of outside advisers to the Food and Drug Administration on Friday. The panel is expected to make recommendations for whether more Americans should receive booster shots.

"Real-world data from Israel and the United States suggest that rates of breakthrough infections are rising faster in individuals who were vaccinated earlier," Pfizer said in its presentation, which was posted on the FDA website. The drug giant is partnering with Germany's BioNTech SE to make the shots.

The decrease in effectiveness is "primarily due to waning of vaccine immune responses over time," rather than the delta variant, Pfizer researchers said in the presentation.

Pfizer shares rose 0.4% as of 11:51 a.m. in New York. BioNTech's American depositary receipts rose 3.2%. Shares of Moderna Inc., the other maker of a U.S.-cleared messenger RNA vaccine, rose 0.3%.

According to a meeting agenda the FDA posted on its website, the Friday panel meeting will include presentations from the Centers for Disease Control and Prevention, FDA staff, researchers from Israel and the U.K., along with Pfizer.

Marion Gruber, one of two top vaccine officials who FDA recently said will step down later this year, is also scheduled to speak. Gruber was co-author of an article in The Lancet earlier this week arguing that booster shots weren't yet necessary for most people. The departure of the two longtime agency staffers is a potential sign of friction over the Biden booster plan.

Officials from Israel will present data from that country on booster protection against infections and severe disease, according to the agenda, and a professor of medical statistics from the University of Bristol will present data on real-world vaccine effectiveness.

FDA staff also posted its report for the panel's consideration Wednesday, summarizing much of the same data that Pfizer presented earlier. Like Pfizer, the staff found that a booster shot of the Pfizer vaccine was safe and raised antibody levels. Still, the staff said it hasn't yet independently reviewed or verified the underlying data or conclusions of some relevant studies, such as the Israel study, which will be summarized in Friday's meeting.

The staff's 23-page briefing paper noted that the likely benefit of a booster shot would depend on how much the third shot reduces disease relative to the first two. If the first two shots are still highly effective, then the efficacy of the booster shot "is likely to be more limited," the staff said. Overall data in the U.S. indicate that the first two shots of the vaccine still protect against severe disease and death, the staff said.

The staff also noted that it is not currently clear whether there will be an increased risk of inflammation of the heart and heart lining after a booster shot, and that potential risks of a booster shot also must be considered. It didn't offer a clear indication of which way the agency was leaning, which it often does before meetings.

While its vaccine continues to provide strong protection against hospitalizations and severe disease in the U.S., Pfizer said in its report, the data from Israel and elsewhere suggest that a reduction in efficacy against infection may be followed by reduced effectiveness against severe disease, especially among vulnerable elderly people.

Early unpublished data from an Israeli health maintenance organization suggest that a third booster dose is highly effective in areas where the delta variant is dominant, according to the Pfizer document. Giving a third dose to people more than 60 years old was associated with 86% effectiveness against testing positive for COVID starting at least a week after the booster, Pfizer said.

Pfizer also detailed immune response results from a final-stage trial of booster shots in over 300 people, showing that a third dose bolstered blood antibody levels. One month after the third dose, levels of the protective antibodies were more than triple what they had been a month after the second shot.

No new unexpected side effects were identified from safety data associated with boosters in the final-stage study, according to the Pfizer report. Consideration of a booster dose six months after a second dose of its shot is warranted, based on similarities between the outbreaks in Israel and the U.S., Pfizer said.

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