Amy Wallace reports on the consequences of the anti-vaccine movement:

In certain parts of the US, vaccination rates have dropped so low that occurrences of some children’s diseases are approaching pre-vaccine levels for the first time ever. And the number of people who choose not to vaccinate their children (so-called philosophical exemptions are available in about 20 states, including Pennsylvania, Texas, and much of the West) continues to rise. In states where such opting out is allowed, 2.6 percent of parents did so last year, up from 1 percent in 1991, according to the CDC. In some communities, like California’s affluent Marin County, just north of San Francisco, non-vaccination rates are approaching 6 percent (counterintuitively, higher rates of non-vaccination often correspond with higher levels of education and wealth).

That may not sound like much, but a recent study by the Los Angeles Times indicates that the impact can be devastating. The Times found that even though only about 2 percent of California’s kindergartners are unvaccinated (10,000 kids, or about twice the number as in 1997), they tend to be clustered, disproportionately increasing the risk of an outbreak of such largely eradicated diseases as measles, mumps, and pertussis (whooping cough). The clustering means almost 10 percent of elementary schools statewide may already be at risk.

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