Used to treat smallpox, monkeypox, and other orthopoxvirus infections by inhibiting the function of a viral envelope protein required for formation of infectious virus particles. It prevents the spread of the virus within the body. Approved for use in humans and considered a key medical countermeasure against poxvirus outbreaks. Also studied for use in animal models and during monkeypox outbreaks for outbreak control and high-risk exposure prevention.