JENNY MCCARTHY, a celebrity who introduced herself to the world on the pages of Playboy 20 years ago, is the proud owner of a Pigasus award, bestowed every April Fool’s day on “the performer who fooled the greatest number of people using the least talent”. Ms McCarthy, an anti-vaccination campaigner, says she is not opposed to vaccination. But she has defended debunked claims that jabs can trigger autism, and reckons her son was cured of his autism through vitamins and diet. More recently the anti-vaccination cause has been taken up by Alicia Silverstone, an actress whose name may now forever be linked to “Clueless” (pictured), a 1995 update of Jane Austen’s Emma in which she starred.

Whooping cough (pertussis), a contagious bacterial infection that is deeply unpleasant for adults and can be fatal for small children, was supposed to have been largely eradicated from the United States, thanks to widespread vaccination. Infections fell from 222,202 in 1941 to 1,010 in 1976. But lately it has made an unwelcome return. In 2012 48,277 cases were reported, the highest figure in over half a century. On June 13th California declared an epidemic; 3,458 cases, including two deaths, have been reported so far this year. Other parts of the country, including Tennessee and Alabama, have also seen big rises, and there has been a worrying climb in measles cases.

Ms McCarthy and her ill-informed followers bear only part of the blame. At least as important is the phasing-out, in the 1990s, of an old vaccine which had nasty side-effects. The immunity conferred by the replacement appears to wear off sooner; health officials urge older children and adults to take a booster jab, but few do. Still, kooky anti-vaccination fears appear to be doing real harm. A study of a 2010 whooping-cough epidemic in California, in which ten babies died, found that areas where many people refused to vaccinate their kids were 2.5 times likelier to have high incidences of whooping cough. No such study has been conducted on this year’s outbreak, although the wealthy coastal enclaves of Marin, Napa and Sonoma counties are among the hardest-hit.

Listening to the ideas of Californian celebrities has not always been bad for Americans, as Ronald Reagan demonstrated. But when it comes to vaccination, probably best to leave it to the experts.