Blankets used by smallpox victims were given by the British to Indian tribes in N.A. during the 18th century. While the actual causative agent of smallpox was not known until very much later, the fact that clothing/bedclothes of the sick could transmit the disease was known (eg: smallpox virus from exfoliating crust containing viable virus on blankets etc). Beginning in the early 18th century the technique of "variolization" was introduced in the west using matter from a smallpox sore to induce a less serious (hopefully) case in a non-immune - this was imported from the east &/or Africa. Modern vaccination, using cowpox material rather than smallpox, was discovered by Dr Edward Jenner towards the end of the 18th century in England.
By WWI smallpox vaccination was essentially universal in all western militaries. while smallpox is a devastating disease - highly contagious airborne & contact, 30-35% mortality in those who have never been vaccinated, about 5% of survivors have serious permanent problems (lungs, blindness etc - ignoring scars) & the sick require a lot of attention, vaccination is straightforward, and almost always completely protective. The current discussions/fears about smallpox as a bioweapon are because no case has been seen since it was eradicated in the 1970s ( a human only disease) and the only known samples of the virus are frozen at CDC in Atlanta & Viron in Novosibersk under tight security so until after 9/11 and concerns about the possibility of some virus being loose out there in a rogue lab, nobody had been vaccinated. That has changed, and the USA (and several other countries) have enough vaccines in storage for their entire [populations should the need rise,,,,,