Medicine: The Disease Year

The one thing certain about each year's polio epidemic is its uncertainty. The disease may spread with a rush early in the summer, reach a peak by mid-August (as in 1953's severe season) and then recede. Or it may come from behind and keep racing ahead into late September—as happened in 1952, one of the two worst polio years in U.S. history. Then, too, the disease usually plays hopscotch across the map. One year it will be most prevalent in the northern Midwest, only to hit the Northeast or the Pacific Coast with special...