> Because smallpox is eradicated, the effectiveness of Tembexa was studied in animals infected with viruses that are closely related to the variola virus. Effectiveness was determined by measuring animals’ survival at the end of the studies. More animals treated with Tembexa survived compared to the animals treated with placebo. FDA approved Tembexa under the agency’s Animal Rule, which allows findings from adequate and well-controlled animal efficacy studies to serve as the basis of an approval when it is not feasible or ethical to conduct efficacy trials in humans.
That's a little disconcerting that there are viruses that are similar, that they're severe enough to kill the host, and that they're willing to use it in tests. Perhaps these viruses they're using aren't nearly as contagious? Or they're not transmissible to humans?