A Lost Uncle

My mother was born in 1932, and she had twin brothers who were born about two years later. While the youngest boys were still infants, their next-older brother, who was in kindergarten, came home from school with whooping cough (pertussis).

The kindergartner missed half a year of school and had to repeat the grade, but one of the twins died. 

This was right around the time the pertussis vaccine were just starting field trials in Michigan, nowhere near my grandparents' home in upstate New York. According to the linked History channel article, in the early 1930s, "6,000 kids in the United States were dying from whooping cough...each year—more than from diphtheria, scarlet fever, tuberculosis or polio."

Whooping cough is no joke, and to this day infants still rely on others to be vaccinated because they can't be fully vaccinated themselves before 12 months.