The non-binding decision by the Vaccines and Related Biological Products Advisory Committee comes as Moderna
The FDA is expected to make a final decision later Friday, while the CDC plans to hold a two-day meeting next week to discuss booster shot distribution in the United States.
Earlier this week, FDA staff had declined to take a stance on whether or not to support third doses of the Pfizer-BioNTech vaccine, saying that U.S. regulators have yet to verify all available data.
"There are many potentially relevant studies, but FDA has not independently reviewed or verified the underlying data or their conclusions," they wrote in a 23-page document published on the agency's website on Wednesday. "Some of these studies, including data from the vaccination program in Israel, will be summarized during the [Friday] meeting."
The staff were referencing an Israeli observational study that showed a third dose of the Pfizer-BioNTech vaccine six months after the second shot boosts immune system protection against infection back to 95%. The data was collected from July 1 through August 30, when the highly-contagious Delta variant was spreading throughout Israel.
"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," the FDA staff added. "Furthermore, U.S.-based studies of post-authorization effectiveness of [the Pfizer-BioNTech vaccine] may most accurately represent vaccine effectiveness in the U.S. population."
Moreover, in a paper published earlier this week in The Lancet, a group of scientists, including staff of the FDA and the World Health Organization (WHO), said that all available data shows that vaccine protection against severe disease continues to persist in the general population, even if immune protection against mild disease begins to wane over time. The scientists concluded that booster shots are not appropriate for the general public at this time, but may be needed in the future.
The FDA's advisory committee said recently that it needs more time to review Moderna's application for general population booster shots.
Moderna on Wednesday released more data on breakthrough infections among those fully vaccinated with its vaccine, which the biotech says supports the need for widespread booster shots.
The company's new analysis of its Phase 3 clinical trial showed that breakthrough infections were less common among participants who were vaccination more recently, suggesting that immunity protection against infection for those who were inoculated earlier started to decrease.
Moderna's analysis has yet to be peer-reviewed.