It’s full-on spring here in Middle Tennessee, and the world is suddenly blooming with infants. There’s a new baby in my family and three more in my small neighborhood alone. All winter, the babies were tucked safely away at home, but now the sidewalks and the parks and the malls have filled up with strollers.

My first child was born during flu season, too, and I well remember the stern admonitions to keep him home till infections waned. But that was 1992. There was no reason for his pediatrician to warn me that I needed to keep him away from anyone who wasn’t vaccinated against other deadly infectious diseases. Before the internet deluded people into believing that an online search was commensurate with a medical degree, vaccination rates were high enough in this country to provide de facto herd immunity.

By the time my last child was born in 1998, the whole conversation had changed. That year, a long since discredited study published in The Lancet, a medical journal, claimed a link between autism and the M.M.R. vaccine, which protects against measles, mumps and rubella. Suddenly parents were turning themselves inside out in an effort to calculate what constitutes a reasonable risk to take with a deeply loved child.

More and more of them concluded that it made no sense to take any risk, however small, when vaccine rates overall made the likelihood of encountering these diseases seem minuscule. As long as most others were accepting the risk of vaccines, their thinking went, there was no need for all parents to do so.

The study that initially raised so many concerns was debunked more than 20 years ago. Today there is absolutely no reason to believe that the measles vaccine causes autism. Nevertheless, vaccination rates continue to fall.

Now a measles outbreak is raging in unvaccinated communities in West Texas and New Mexico, and a longtime anti-vaccine activist oversees health policy in this country. Robert F. Kennedy Jr., the secretary of health and human services, can bring himself to offer only the barest acknowledgment that vaccines prevent measles. He urges useless and unscientific alternatives and insists that vaccination is a personal choice.