Other parents fret about thimerosal, a preservative that contains trace amounts of mercury. Not only were these amounts minute and safe, but thimerasol has now been eliminated from all vaccines, with the exception of multi-dose flu shots. Often these parental conversations then turn into new-agey free-for-alls, where vaccines somehow join the list of conventionally grown avocados and unfiltered tap water as lethal menaces.
Nonetheless the issue runs straight into the classic American tension between individual choice, which is good, and public health and safety, which is also good. All states save Mississippi and West Virginia allow a religious exemption for vaccinations, and 20 states also allow a more vague philosophical exemption. So what can health officials do?
Principally they can try to educate more parents with good science rather than internet drivel. Mr Pan is also pushing a law through California’s legislature that would require parents to discuss vaccination with their paediatricians. If the parents still want to opt out, their doctors would have to sign a form to show that the parents were told about all the risks and benefits.
John Talarico, the chief of immunisation in California’s public-health department, says that vaccination rates will probably keep dropping in some demographic groups for a while longer. The root problem is that today’s parents are the first in history with no memory of the maiming and killing caused by polio, tetanus, diphtheria or measles. At some point an epidemic will remind them.