FDA on Tuesday released data on potential Covid-19 booster shots for Moderna and Johnson & Johnson (J&J) vaccine recipients, but the agency's staff chose not to take a position on whether those boosters were necessary ahead of the meeting of an independent advisory panel.

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FDA releases data on booster shots

In its application, which is requesting booster authorization for the same population groups already authorized for a booster dose of the Pfizer-BioNTech vaccine, Moderna argued a half-dose booster shot of its vaccine is necessary because the vaccine's protection against mild Covid-19 cases drops over time. The company noted that neutralizing antibodies start waning six to eight months after a person receives their second dose, adding that there is "real-world evidence of reduced effectiveness against the delta variant."

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FDA staff, however, noted that "[s]ome real-world effectiveness studies have suggested declining efficacy of Moderna Covid-19 vaccine over time against symptomatic infection or against the delta variant, while others have not."

Neither Moderna nor FDA said any current data suggests waning effectiveness at preventing severe Covid-19 cases or death.

According to Moderna, the average antibody level of participants in a study was 1.8 times greater following a booster shot than it was following the second shot. The booster also increased neutralizing antibodies at least fourfold in 87.9% of participants compared to the second dose, Moderna said.

FDA's documents also discussed potential side effects of Moderna's booster shot, noting that analyses of insurance claims data conducted by FDA found the number of myocarditis cases in men ages 18 to 25 ranged between 72.4 per million vaccinated to 283.7 per million.

"It is currently not known if there will be an increased risk of myocarditis/pericarditis or other adverse reactions after a booster dose of the Moderna Covid-19 vaccine," FDA wrote.

The documents released by FDA did not include a detailed analysis on the effectiveness of a J&J booster shot. However, J&J in the documents said that booster shots of its vaccine improved protection against Covid-19, including against severe cases of the disease, and increased immune system response against variants of the virus.

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J&J said that a booster dose of its vaccine could be administered as soon as two months after a person's first dose, but it recommended the booster shot be administered after at least a six-month gap to prompt a stronger immune response. However, an agency analysis released on Wednesday questioned the strength of J&J’s booster shot evidence, citing concerns over the sensitivity of a test used to measure the immune response of a six-month-boost. FDA also stated it did not have enough time to review much of the raw data from the company’s clinical trials ahead of this week’s VRBPAC meeting.

The FDA documents also included data on the side effects of J&J's vaccine, noting some rare reports of acute liver failure, autoimmune disorders, blood clots, and heart inflammation. However, none of the reports were common enough to raise significant new safety concerns.

What's next

In the documents, FDA staff did not take a specific stance on the necessity of booster shots for either the Moderna or J&J vaccine. Currently, booster doses are approved only for certain recipients of the Pfizer-BioNTech vaccine.

On Thursday and Friday, FDA's independent vaccine advisory committee is expected to discuss whether to recommend booster shots of Moderna and J&J's vaccines. FDA has proposed the committee consider a potential recommendation for the same population groups already authorized for a booster dose of the Pfizer-BioNTech vaccine.

FDA is not required to follow the recommendations of the advisory committee. However the agency typically does so, the New York Times reports. (LaFraniere, New York Times, 10/12; Anderson, Becker's Hospital Review, 10/12; Herper, STAT News, 10/12; Schwartz/Loftus, Wall Street Journal, 10/12; Neergaard/Perrone, Associated Press, 10/12; Zimmer/Weiland, New York Times, 10/13)