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Take a look at the list of conditions that have treatments available thanks to what’s known as the “Animal Rule” and you’ll see a rogues’ gallery of plagues you hope never see the light of day. There’s smallpox, anthrax, and, well, the actual plague.

The Animal Rule is a Food and Drug Administration policy that gives the agency the authority to approve treatments without efficacy data from human clinical trials in instances when those trials aren’t possible. Instead, regulators rely on data from animal models to give the treatments the green light.


The rule has gotten attention recently because Tpoxx, or tecovirimat, was approved under the rule to treat smallpox and is now being used to treat people infected with monkeypox in the unprecedented global outbreak.

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