Assessing a drug for an eradicated human disease: US Food and Drug Administration review of tecovirimat for the treatment of smallpox.

The development and ultimate approval of tecovirimat for the antiviral treatment of smallpox, a disease that has been eradicated from the world for nearly 40 years, required a unique regulatory approach based on the US Food and Drug Administration's Animal Rule. We summarise the regulatory pathway and describe the challenges involved.