The FDA has issued emergency approval for a vaccine only once, for an experimental anthrax vaccine in 2005. The FDA had originally declined to issue an emergency use authorization, but the Department of Defense pushed for one due to concerns over possible anthrax attacks against U.S. military forces.
Vaccine-associated enhanced respiratory disease
A clear concern in the FDA’s guidance for the coronavirus vaccine is whether vaccine candidates might cause enhanced respiratory disease —not only failing to decrease the severity of COVID-19, but causing it to get worse.
While rare, data from animal studies in some vaccine candidates for other coronaviruses, such as SARS-CoV and MERS-CoV, has raised concerns regarding COVID-19, the FDA said.
Infecting healthy people to test a vaccine
The FDA also said challenge trials could be considered to test COVID-19 vaccines. In those trials, healthy people are intentionally infected to see if the vaccine keeps them from getting COVID-19.
That might be necessary if there were so little SARS-CoV-2 virus circulating that it was no longer possible to study whether a vaccine was effective. If there’s no chance people who’ve gotten test injections could get infected, it wouldn’t be possible to test whether the vaccine works.
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The agency made clear in its document that challenge trials are not ideal. “Many issues, including logistical, human subject protection, ethical, and scientific issues, would need to be satisfactorily addressed,” it said.
Side effects, public trust could undermine vaccine
There are several possible downsides to issuing a vaccine prematurely.
Side effects and bad outcomes may be rare enough that they appear only when many people receive the vaccine, or after enough time has passed for them to appear. That could give fuel to anti-vaccine groups that claim without evidence that vaccines are harmful.
Some people could be scared away from the vaccine if they don’t believe it has been properly and thoroughly tested. If people won’t take the vaccine, it doesn’t matter how soon it’s available.
Paul Offit, a vaccine expert at the University of Pennsylvania, has spoken of the possibility that a vaccine could be unveiled as an “October surprise” and the harm that could cause. The FDA’s guidance made him less concerned, he said.
“I think this is all very reassuring,” he said. “Now all they have to do is follow their own guidelines.