As the days grow cooler and the sun drops toward the southern horizon, we can be certain that we're moving into the vaccine season as well as the fall season. With the start of school comes the requirement that children be vaccinated against disease, an important requirement because schools can serve as distribution points for diseases. That's why it's also important to pay attention to the latest findings on the link between autism and vaccines.

The news is that there isn't any news - again. Researchers recently repeated a decade-old study which had suggested a link between the onset of childhood autism and the mumps-measles-rubella vaccine. Their more sensitive modern techniques erased the link. And yet the result was not enough to satisfy one advocate who in a news report insisted on more testing of more vaccines, and here we come to a central problem: the difference between belief and evidence.

Belief is not evidence, but many advocates for the autistic cling to the belief that vaccines are to blame for autism. For years these advocates blamed vaccines because they contained thimerosal, a mercury-based preservative. Thimerosal has gradually been eliminated from all but a handful of vaccines, yet the incidence of autism has continued to increase. Still, the vaccine belief persists.

Autism may be the result of other disorders; some scientists speculate that some undefined gastrointestinal difference causes whole-body inflammation and that this brings on brain changes. Earlier this year, scientists wrote that one unstable region of one chromosome is associated with autism and a number of other disorders. By insisting on study after study to justify their beliefs and by ignoring other evidence, advocates for autistic people may push aside whatever the truth turns out to be, and thus they may bury the very result they desire.

Beyond hurting their own cause is the very real risk that they will hurt others, for one still hears parents worry aloud about the potential side effects of vaccines. This is despite the fact that the original 1998 study linking autism to the MMR vaccine has been refuted time and again, and the fact that 10 of the original 13 scientist-authors later retracted their assertion. After the original article appeared, in a British medical journal, the MMR vaccination rate in some parts of Great Britain dropped from 90 percent to 70 percent over several years, and there was an expected consequence: measles, mumps, and rubella had a resurgence.

If you have a child whose health is delicate, it may be worth discussing the vaccination schedule with your physician, but it's dangerous to decide on your own to not vaccinate your children. These diseases are still very real, and if we drop our guard by stopping vaccination, they will hit and hit hard. We'll have a good old-fashioned plague, but we'll know whom to blame.