In 1998, the British medical journal The Lancet published a study that, indirectly, led to the first outbreak of measles in the British Isles in decades. How could one study in a journal that’s mostly read by scientists and doctors have such a far-ranging impact? The study argued that autism symptoms could be explained by the use of the Measles-Mumps-Rubella (MMR) vaccine.

Since then, an entire movement of parents and activists sprung up — including, most notably, Jenny McCarthy — who were convinced that the cause of their children’s autism were nefarious pharmaceutical companies who were hiding the truth so that they could sell more vaccines. In 2005, activist and lawyer Robert F. Kennedy Jr. published a piece in Rolling Stone alleging that there was a conspiracy of pharmaceutical companies and the U.S. government to repress evidence of the vaccine-autism connection.

This past week, however, The Lancet retracted the study. Although the scientific community had rejected the study’s conclusions for years, The Lancet was finally forced to formally retract the study when Britain’s medical regulator, the General Medical Council, sanctioned the lead researcher behind the study, Dr. Andrew Wakefield, for not disclosing payments he got from lawyers representing parents who’s kids had received the vaccines and for conducting unnecessary, unhealthful tests on children.

The study, which was based on tests done on all of 12 children and were followed up by a statement by Dr. Wakefield recommending that parents not get the vaccine, caused a plummet in vaccinations in the UK, well past the 95% threshold needed for so-called “herd immunity.” In England, vaccination rates for measles, mumps, and rubella cratered in 2004 when only 80% of children were vaccinated. Subsequently, there were 1,000 cases of measles in the U.K. Measles, of course, was previously thought to have been eliminated in the modern world. There were even more cases of mumps: in 2004, there were more than 16,000 reported mumps cases in England and Wales, a fourfold increase over the previous year.  In 2008, “Fourteen years after the local transmission of measles was halted in the United Kingdom,” there was a measles epidemic.

The irony is that in the developing world, parents and kids would love to have access to a measles vaccine. In 2008, some 164,000 died of the disease despite a vaccine being available; 95% of those deaths were in poor countries where there isn’t the medical infrastructure to distribute the vaccine. Unfounded concerns over the MMR vaccine seem to be a first-world luxury.

The populist movement against vaccines, and more specifically, the totally bogus claim that the MMR vaccine causes autism, is not just another example of a great number of people misunderstanding science — it’s a real movement that has real consequences for the kids whose rights to health care are being violated by their sadly misinformed parents. The vaccine delusion has even seeped into politics. In 2002, Indiana Republican Dan Burton took up the cause, saying that “My only grandson became autistic right before my eyes — shortly after receiving his federally recommended and state-mandated vaccines.” But obscure Indiana congressman aren’t the most prominent leaders of this movement: celebrities are.

Jenny McCarthy, who became famous posing for Playboy, has directly blamed vaccines for causing her son, who was otherwise developing normally, to develop symptoms connected with autism. Since then she has started a foundation (which supports Dr. Wakefield) and has become an advocate for untraditional treatments for autism such as chelation therapy. Chelation therapy is in widespread use among alternative medicine practioners and removes heavy metals — like mercury — from the body. There is, not surprisingly, no scientific evidence that chelation therapy does anything to mitigate the symptoms of autism.

McCarthy’s situation, minus the relentless and reckless self-promotion, is a perfectly representative example of why the vaccine-autism connection has such a powerful grip on so many. The symptoms of autism often first manifest themselves as missed developmental landmarks, such as not being able to speak. Parents often describe, or retrospectively “remember,” a radical shift in their child’s behavior. They go from functioning, happy and normal to distant, sick and alien.

That some parents become aware of their children’s autism at around two years, as in the case of McCarthy, means that they are more likely to attribute their child’s condition to the MMR vaccine, which is often given to children at 15 months. Up until then, their child appears to be “normal,” and then their expectations are totally upended and they look for explanations. And since many people just see vaccines as something they need to get their children without any understanding of why they’re doing so, it is easy for them to scapegoat  the vaccine for such a dramatic apparent change in their child. Or, as McCarthy puts it, after her son was given the MMR shot, “soon thereafter — boom — the soul’s gone from his eyes.”