Few people in the United States today are old enough to remember when diphtheria was a common and very dangerous disease. My mother, who is almost 100 years old, remembers when she contracted diphtheria as a teenager, how she lost all her hair, and how her parents despaired of her survival. Mom made it through that long and serious illness, but many other people did not.
As for me (and let's not discuss how old I am!), I had and recovered from measles, rubella, mumps, and chickenpox. I was unharmed by those diseases (not even a chickenpox scar), but lots of other kids had lasting damage from high fevers. I remember the little girl down the street who lived, but with severe mental retardation as a result of brain damage. I also recall the rejoicing with which the Salk polio vaccine was received, and how every parent breathed easier in the summers and let their children go to the public swimming pools that had been closed during polio epidemics.
Today, I find myself shocked to hear of parents who refuse to allow their children to be vaccinated. I cannot imagine that they have really thought through what it would mean to their families or communities to return to pre-vaccination days. I do understand, though, that in many cases they have the mistaken belief that their resistance to vaccination will protect their children from developing autism.
It is certainly true that when thousands of infants, toddlers, and preschoolers are immunized, a small proportion of them will at about the same time be diagnosed as autistic. The period of development when most vaccination takes place is also the period when characteristics of autism are usually noticed for the first time. For most families, the first serious symptom of autism they notice is that their toddlers do not talk or communicate in other ways, although other children of the same age are chattering away. Because there is a lot of variation in speech development, pediatricians often tell families not to worry about language until the child is 2 ½ or 3 years old. When the language delay is finally recognized as a serious one, families may or may not remember noticing unusual behaviors earlier on---- but they are likely to remember a recent immunization..
It's a common human logical error to assume that when things happen at about the same time, one must have caused the other. This assumption is sometimes described by the words "post hoc, ergo propter hoc"--- "after this, therefore because of this". It's all too easy to think that if a diagnosis of autism follows immunization, the disorder must have been caused by the immunization. But a plausible connection like this is not the same as evidence of causation, and no such evidence exists. In fact, there is quite contrary evidence; for example, although boys and girls are immunized in the same proportions and at the same ages, about four times as many boys as girls are diagnosed as autistic. If vaccination were the simple cause of the disorder-- or even one of the causes--- we would expect equal proportions of boys and of girls to develop autism.
One of the reasons people tend to consider that some event causes autism in a previously well-developed child is that autism and other pervasive developmental disorders sometimes appear to come on very quickly. Although some children with autistic-like symptoms are reported to be atypical in their development from a very early age, others are much like their brothers and sisters until toddlerhood. Children with the mutation causing Rett syndrome are a case in point. The Rett children whose behavior has been studied are all girls, because boys with this mutation die of respiratory problems in early infancy. The girls appear healthy for months, but as toddlers they begin to regress and lose the language and other social abilities they have developed. They become irritable, lose mental ability, and show stereotyped handwringing movements.
Anyone looking at an individual Rett syndrome child could easily jump to the conclusion that this list of symptoms was caused by an event like vaccination which occurred not long before the child's development became less typical. But that would not be the case. Rett syndrome has been shown to result from a genetic condition that arises by mutation rather than being inherited from the parents. Biologists have identified a similar genetic condition in mice and can either cause or cure the mouse condition; unfortunately, they cannot yet treat human beings who have the mutation.
Geneticists have identified a number of genes that seem associated with autism, but do not yet have a clear picture of the events that lead to autistic development. Perhaps when this is achieved we will no longer hear of parents denying their children the benefits of vaccination out of fear of autism. Until that happens, we need to spread the word that withholding vaccination cannot prevent autism, but it can cause children and others to be the victims of serious diseases.
