When the psychiatrist Leo Kanner first defined autism in 1943, it was estimated that 4 to 5 children per 10,000 were affected by the condition. Today, the Centers for Disease Control puts that number at 1 in 36, or almost one child in every classroom. If any other medical condition—blindness, epilepsy, or paralysis—showed a spike like this, it would trigger a pandemic-level outcry. But after parental panic across the West and a search for a causal villain in vaccines that followed reports of 1