It’s not clear smallpox-infected blankets even worked.
It’s also not clear whether or not the attempt at biological warfare had the intended effect. According to Fenn’s article, the Native Americans around Fort Pitt were “struck hard” by smallpox in the spring and summer of 1763. “We can’t be sure,” Kelton says. Around that time, “we know that smallpox was circulating in the area, but they [Native Americans] could have come down with the disease by other means.”
Historian Philip Ranlet of Hunter College and author of a 2000 article on the smallpox blanket incident in Pennsylvania History: A Journal of Mid-Atlantic Studies, also casts doubt. “There is no evidence that the scheme worked,” Ranlet says. “The infection on the blankets was apparently old, so no one could catch smallpox from the blankets. Besides, the Indians just had smallpox—the smallpox that reached Fort Pitt had come from Indians—and anyone susceptible to smallpox had already had it.”
The most important indication that the scheme was a bust, Ranlet says, “is that Trent would have bragged in his journal if the scheme had worked. He is silent as to what happened.”
Even if it didn’t work, British officers’ willingness to contemplate using smallpox against the Indians was a sign of their callousness. “Even for that time period, it violated civilized notions of war,” says Kelton, who notes that disease “kills indiscriminately—it would kill women and children, not just warriors.”