IIRC, there's no antidote for smallpox. Only prior vaccination will help with smallpox which kills about 1/3 of those infected.
First off, I'm pretty sure there is something which can be given for smallpox after infection, but I could be wrong. Just something I remember from my stay at NBC Warfare School. OTOH, I'm pretty sure that a lab weaponized strain is going to be tougher to deal with; much more lethal and fast acting. I seriously doubt that there are antitoxins or antidotes available to anybody from any nation for these, except what may be carried in a national stockpile for use by the military, only.