FDA official casts doubt on 'challenge trials' for Covid-19 vaccine

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A top FDA official overseeing vaccine approvals raised doubts Wednesday about the possibility of intentionally infecting people with the coronavirus to see whether vaccines work, saying that could represent “ethical heartburn” because there’s still no easy way to treat the potentially severe disease.

Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, also defended the FDA’s recent guidance requiring Covid-19 vaccine candidates must be at least 50 percent more effective than a placebo.

“I think we got to the perfect spot there,” Marks said at an industry event, adding that FDA has received criticism from all corners. “If you go much lower than 50 percent, then you go to bounds of very little efficacy … but 70 to 80 percent might mean there isn’t a vaccine until herd immunity occurs naturally."

The ethical debate: Typical vaccine studies enroll tens of thousands of healthy volunteers in separate vaccine and placebo arms under the assumption that a certain amount of each group will come in contact with the virus. Human challenge trials are controversial since test subjects are intentionally infected, but the idea has gained traction as the pandemic rages on and multiple vaccine-makers are trying to line up trial participants.

Thirty-five House members, including former HHS chief Donna Shalala, wrote to HHS in April urging the agency to consider human challenge studies. The World Health Organization in May published guidance that green-lighted ethical versions of the trials. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease, told POLITICO last month that the option was on the table, but he hoped researchers would not need to use that approach.

Challenge studies have typically been used for mild diseases with known treatments like a common cold or diarrhea, Marks said Wednesday during an Alliance for a Stronger FDA event. There are still too many questions about how Covid-19 affects people, he added. It’s not clear why some people get severely ill while others show no symptoms, or why some have lung problems while others develop blood clots.

“If something bad happens, you don’t have a perfect fix for it,” Marks said. Still, he didn’t rule out the option of a challenge trial.

“It’s not a no, it’s a ‘We’ll see what you submit,’” Marks said.

The pressure is on: President Donald Trump has promised a vaccine would be available by the end of the year even as health officials try to hedge expectations. Multiple potential Covid-19 vaccines are hurtling through clinical trials, with several expected to start the final, sweeping phase III trial by the fall. Two are expected to begin this month — one for a Pfizer candidate and another for a candidate developed by NIH and Moderna.

The speed of vaccine development and recent FDA stumbles, including the hasty emergency use authorization — and subsequent reversal — for hydroxychloroquine have raised alarms with current and former officials concerned the agency would be pressured to approve a candidate on sparse data.

Marks said that safety has been top of mind as vaccine trials go at record speed.

“At the end of the day, we’ll have to be able to look at the public and say corners were not cut,” Marks said.

Zachary Brennan contributed to this report.



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