When Dr. Paul A. Offit published “Autism’s False Prophets” in 2008, he elected to skip the usual round of book signings. His defense of childhood vaccinations so enraged some people who consider them a cause of autism that he was getting credible death threats. Others might have chosen to flee the public arena after that, but not Dr. Offit, the chief of infectious diseases at Children’s Hospital of Philadelphia, whose appetite for the good fight seems only to have grown. Over the last decade he has become a leading debunker of mass misconceptions surrounding infections and vaccines, and now he...