Experts concerned by limited safety data required by FDA for COVID-19 vaccines

A number of panel members and outside experts speaking at an FDA advisory committee meeting expressed concern about the limited safety data that the agency is seeking before considering emergency-use approval of a vaccine against COVID-19. Panel member Hayley Altman-Gans said "they haven't gone far enough" in terms of safety.

The FDA is requiring a vaccine to work in at least 50% of people and for companies to collect two months of safety data on at least half of clinical trial participants. However, at the meeting, panel members and outside researchers suggested that the safety requirements are not enough, with Archana Chatterjee noting that the public has a lot of concern around this area.

Worries over reduced effectiveness, trial designs

Panel member Amanda Cohn expressed concern that the efficacy of a vaccine that just meets the 50% threshold after two months may see reduced effectiveness a few months later. "Very rarely do we look at [vaccine efficacy] so shortly after completing a series," Cohn said. Members of the committee also warned that if a vaccine turns out to be less effective than promised, or have safety problems, it could undermine public confidence for years to come.

Some outside experts also questioned the design of ongoing late-stage trials, with Diana Zuckerman of the National Center for Health Research suggesting that the studies "have serious design flaws." Zuckerman also believes the two-month follow-up requested by the FDA is too short to establish how long a vaccine will work. She added that the trials are too geared to preventing mild infections, and may not show whether they prevent severe infections and hospitalisations.

Questions over placebo recipients

The panel also discussed whether study participants that receive a placebo injection should be informed when a vaccine is deemed to be safe and effective. A federal official said that drugmakers should not advise subjects that they have received a placebo, even if preliminary data show that the vaccine is safe and effective.

Ahead of the advisory meeting, FDA deputy director Doran Fink noted that once a vaccine gains emergency-use authorisation, an application for full approval should follow as soon as possible. Fink explained that to meet the more-stringent criteria for full approval, it requires that drugmakers not reveal who is getting a placebo so they can generate more robust data on how well the vaccine works and how long it lasts.

Prior to the meeting, both Johnson & Johnson and Pfizer raised concerns about the ethics of leaving participants on a placebo if the vaccines have been shown to work. "If Pfizer's vaccine is granted emergency-use authorisation, we would propose to amend our ongoing study to allow cross-over of eligible placebo subjects to the active vaccine arm if they wish to do so at any time," remarked Peter Honig, the company's senior vice president of global regulatory affairs.

For further discussion of the advisory committee meeting, read ViewPoints: FDA makes its case for vaccine EUA.

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