Like most American children of my generation, I lined up with my classmates in the mid-1950s to get the first vaccine for polio, then causing 15,000 cases of paralysis and 1,900 deaths a year in the United States, mostly in children. Likewise, we lined up for the vaccine against smallpox, then still causing millions of deaths worldwide each year. I’ve continued to update my immunizations ever since, including a few exotic ones for National Geographic assignments abroad, among them vaccines for anthrax, rabies, Japanese encephalitis, typhoid, and yellow fever.

Having grown up in the shadow of polio (my uncle was on crutches for life), and having made first-hand acquaintance with measles (I was part of the pre-vaccine peak year of