It has been recorded that many outbreaks of yellow fever from 1668 to 1853 occurred in the U.S.

The first outbreak started in New York  of 1668, America was still a child, living in England's house alone.

England was away on a business trip, so America was left to deal with the outbreak by himself.

That's why Canada would sneak over to England's house to help America deal with the yellow fever.

"Best brother out there, Canada." He hugged him. "Thanks brother."
                 《☆》《☆》《☆》

Aw, go Canada, my home and native land, xD. I love this headcanon and support it with my heart because Canada would be the one to do that. Not to mention, my twin little sisters did that when one of them gets sick.