Last Thursday, three special masters in a federal “vaccine court”  bluntly ruled that vaccines do not cause autism. Thousands of families with autistic children are thus not entitled to compensation from the National Vaccine Injury Compensation Program. Drawing on 5,000 pages of transcripts studded with academic footnotes and expert reports, these special masters made the right call.

One of my first forays in the internet badlands was a February 2008 HuffPo column titled “No, Vaccines aren’t behind the rise in autism.” That column harshly criticized the otherwise-enjoyable ABC series, “Eli Stone” for airing a thinly-disguised and quite misleading account of the thimerisol controversy. I’m still getting hostile emails for that one, but I stand behind what I wrote: Vaccines must be carefully regulated. Some vaccines have harmed specific children. Yet the alleged link between vaccines and the rising prevalence of diagnosed autism has been thoroughly debunked. There is simply no scientific debate here. I won’t recap the findings, but if you want more, check out the websites of the Institute of Medicine here, and the American Academy of Pediatrics here.

Alas, the same social currents that lead people to fear vaccines lead them to distrust the messengers and messages that might assuage these fears. Elaine Showalter's Hystories: Hysterical Epidemics and Modern Culture explained how unfounded beliefs spread through an interaction of families in pain, underlying cultural anxieties, charismatic issue advocates, and the media.

On one side, the vaccine-autism controversy features heart-wrenching testimony from parents such as Jenny McCarthy who faithfully took their child in for shots, only to witness the onset of autism following close behind. On the other side, the debate features…. Big Pharma. Need I say more? This issue taps into widespread distrust of the financial and cultural hegemony of scientific medicine. It touches our primeval fear of putting strange chemicals into our bodies in novel combinations to do strange things--all in the service of preventing diseases that, to all outward appearance, were eradicated in America in the “Leave it to Beaver” era.

The public health consequences of these myths are real. U.S. measles cases have markedly increased. Citing January-July 2008 data from fifteen states and Washington DC, the New York Times reports,

Most of those who were sickened were unvaccinated or had an unknown vaccination status. Sixteen were younger than a year old, too young to have been vaccinated. But two-thirds of the rest--or 63 people--were unvaccinated because of their or their parents' philosophical or religious beliefs.

Immunization rates are lower in Britain, and have also been traced to parents declining to vaccinate their children. Resurgent measles has proved especially serious in Britian in recent years. The combined measles, mumps and rubella (MMR) vaccine is our standard weapon against measles. MMR also has attracted the most controversy for its alleged autism links. About 95 percent of American school-age children have received at least one MMR shot.

We don’t have to vaccinate everyone to protect ourselves against an infectious disease. We must merely vaccinate enough people to reach what epidemiologists call “herd immunity,” in which we cross a critical threshold sufficient to prevent outbreaks from taking hold. When herd immunity is achieved, local outbreaks may occur, but they cannot become self-sustaining.

Every infectious disease has its own critical threshold, which depends on how people mix to spread the disease, the biological properties of the infectious agent, and other factors. Alas measles is exceptionally infectious. By most estimates, one must maintain more than 90 percent coverage to keep it at bay.

On the whole, American society does a pretty good job maintaining herd immunity. Unfortunately, particular communities and subcultures fall far short of this threshold. Public health authorities become especially alarmed when a measles case is reported within a parochial school that serves many families opposed to vaccination. Some other communities and subcultures—some relatively educated and affluent—also have low immunization rates that allow measles to gain a foothold.

This is a serious public health problem. In my view, media figures such as Oprah do a great disservice by giving sincere but misguided parents airtime to say things that aren’t true.

In light of this history, pharmaceutical companies, medical providers, and the public health community are especially tempted to crow about Thursday’s ruling. I hope we resist that temptation. Our society includes many economic, cultural, and religious constituencies which seek to deny or obscure scientific findings. Given our ignorant and lazy popular culture, it is depressingly easy to confuse millions of people.

The vaccine-autism meme draws force from a particular anti-corporate, anti-medical populism. So Thursday’s decision was greeted with satisfaction by the Wall Street Journal editorial page, which can for one moment affect the anti-populism of H.L. Mencken before returning to its familiar terrain haranguing the cultural (thus presumed liberal) elite. Conservatives seem visibly less indignant about corporate anti-scientific arguments that reflect balder economic motives. (Case in point: My TNR colleague Brad Plumer posts a great essay debunking George Will’s surprisingly meretricious denial of global warming.)

Thursday’s court decisions should improve public debate. I would be surprised if these cases really settled things. Parents believe that vaccines cause autism because they do not trust medical authorities and pharmaceutical companies. Thus they do not believe claims that vaccines are safe. Such distrust runs deep, and is hardly confined to vaccination issues. It is impossible to understand the popularity of complementary and alternative medications, for example, without acknowledging their appeal in offering patients an escape from traditional medicine.

As any good pediatrician will admit, we cannot debunk myths about vaccines by correcting or belittling misguided parents. The only effective strategy is to act with the transparency, effectiveness, respect, and care that earn people’s trust. Right now, we do not earn the trust of many beleaguered parents. Until we do, some will embrace harmful rumors that defy our epidemiological logic, but that ring true to their own deeply-held experiences.

Harold Pollack is a public health policy researcher at the University of Chicago's School of Social Service Administration, where he is faculty chair of the Center for Health Administration Studies. He is a regular contributor to The Treatment.

By Harold Pollack