[hinckley buzzard]

Smallpox is caused by the Variola virus, so antibiotics have never been useful against it, "hardened" or otherwise. Your comment, or perhaps your source, makes no sense.

[HogsBreath]

Thanks for the correction; I should have caught that. According to the author, the Soviets were weaponizing smallpox (a strain they referred to as India-1) AND the plague. The plague (Yersinia pestis), being a bacteria, is susceptible to anti-biotics and was ‘hardened’ by exposing it to anti-biotics and using the surviving strains. I guess I merged the details in my memory!