Of a force of 10,000 Continental Army soldiers in Quebec, about 5,000 fell ill with smallpox. A British commander may have deliberately intended to spread the disease by sending recently variolated civilians into Continental Army encampments.
The Continental task force commander, Major General John Thomas, died of smallpox. The unit retreated southward in May 1776. Arguably, this defeat preserved the status of the northern British colonies, permitting Canada to become the separate country it is today. John Adams wrote:
“Our misfortunes in Canada are enough to melt the heart of stone. The smallpox is ten times more terrible than the British, Canadians and Indians together. This was the cause of our precipitate retreat from Quebec.”