LAST WEEK, my 15-month-old son got his Pentacel shot, which contains vaccines for diphtheria, tetanus, whooping cough, polio, and a form of influenza that can cause bacterial meningitis. By rights, I should have felt relieved: He’s now protected from a pack of dread diseases. But I was nervous for days, watching his every move. Was he still making eye contact? Saying “Hi, Dada’’? Or was this the moment he’d slip away?

Maybe I’ve read too many stories about parents like Doug Flutie, who swears that his child was normal, got some shots, and changed. But I know that few things strike terror into parents’ hearts like the dramatic increase in autism diagnoses, now estimated at one in 100 American children.

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