There’s a reason that we associate the whooping cough with the Dickensian: It is. The illness has, since the introduction of a pertussis vaccine in 1940, has been conquered in the developed world. For two or three generations, we’ve come to think of it as an ailment suffered in sub-Saharan Africa or in Brontë novels. And for two or three generations, it was.

Until, that is, the anti-vaccination movement really got going in the last few years. Led by discredited doctors and, incredibly, a former Playmate, the movement has frightened new parents with claptrap about autism, Alzheimer’s, aluminum, and formaldehyde. The movement that was once a fringe freak show has become a menace, with foot soldiers whose main weapon is their self-righteousness. For them, vaccinating their children is merely a consumer choice, like joining an organic food co-op or sending their kids to a Montessori school or drinking coconut water.

The problem is that it is not an individual choice; it is a choice that acutely affects the rest of us. Vaccinations work by creating something called herd immunity: When most of a population is immunized against a disease, it protects even those in it who are not vaccinated, either because they are pregnant or babies or old or sick. For herd immunity to work, 95 percent of the population needs to be immunized. But the anti-vaccinators have done a good job undermining it. In 2010, for example, only 91 percent of California kindergarteners were up to date on their shots. Unsurprisingly, California had a massive pertussis outbreak.