The British repeatedly gave blankets they new had smallpox. Todays evidence is that nothing happened, the virus was already dead. But it's worth mentioning that from a Native American perspective this still happened, they received blankets and shortly after they had an epidemic. Whether they contracted it from the blankets or not is sort of besides they point, they intended to infect Native Americans with smallpox and local tribes ended up having a smallpox epidemic shortly after. Maybe they found another way, or maybe someone got infected by coming in contact with the British during one of the conflicts. But does it really matter? With or without blankets they still murdered millions (thought to be the largest genocide in human history) of native people on their own land simply because they wanted to steal all the land. They didn't need smallpox to do that, they did it with guns, and forced starvation.