Too many too soon: that's Jenny McCarthy's rallying cry. The disingenuous activists of the antivaccine movement use this motto as a foot in the door, claiming that they are not truly "anti-vaccine", just pro-"safe vaccines". This is despite the fact that vaccines have proved themselves to be one of the safest and most effective medical interventions in human history.
Pediatricians in the community are struggling with the fallout of the antivaccine propaganda, having to spend their finite patient-care hours trying to explain to parents why they should vaccinate their children properly. While they are fighting this difficult but good fight, popular celebrity doctors such as Dr. Bob Sears and Dr. Jay Gordon are shouting about the horrors of evidence-based vaccination and offering their own made-up alternatives.
In addition to promoting the resurgence of several infectious diseases, these "activists" have forced the medical and scientific community to waste valuable resources studying the same questions again and again. And when the question is answered, the infectious disease promoters yank up the goalposts and start running. There is no data set that will ever convince Jay Gordon, Jenny McCarthy, or Bob Sears that current vaccine recommendations are safe and effective. There is also no external evidence that will cause them to alter their own recommendations for "alternative schedules".
But given the public health importance of vaccination, we are forced to counter the propaganda. A new study in the journal Pediatrics does just that. This study appears to have been designed to answer the questions frequently raised by antivaccine activists. When thimerosal was proved to be innocuous they moved on to "toxins". When this gambit failed, they moved on to "too many too soon". As this argument has unraveled, they have called for "vaccinated vs. unvaccinated" studies, prospective studies which follow children who are and are not vaccinated and look at different rates of autism. Epidemiologists have been all over the question of causation, but not surprisingly, the antivax crowd hasn't been satisfied with them to date. The new study adds another layer of evidence to what we already know: vaccines do not cause autism.
But this study goes one step further and asks the question, "is it really 'too many too soon?'" The study's conclusion is in its title: "On-time Vaccine Receipt in the First Year Does Not Adversely Affect Neuropsychological Outcomes." The authors used vaccine data from several thousand children. They compared children who followed the recommended vaccination schedule in the first year of life vs. those who did not, and compared neurological outcomes 7-10 years later. The data were unequivocal: there were no significant neurologic problems present in the "off-schedule" group compared to the on-time group. This very strongly argues against "too many too soon".
There are two rational complaints likely to be raised by the antivaccination crowd. One is potential conflicts of interests in the authors. Both authors have disclosed various types of financial support from drug companies in either research funding or speaking fees. This does not mean the data are tainted, but it does mean the data require close scrutiny. Neither the data nor conclusions in this study seem to suffer from undue influence, as far as I can tell from my reading. There is always the possibility of outright fraud, something that would be hard to detect in reading a study, but I see no reason to suspect this. Also, their data and conclusions track very closely with what we know from previous studies on vaccination and neurologic problems.
The second question likely to be raised is whether this study captured the correct populations. The data make clear that when the recommended vaccination schedule is followed in the first year of life, there are no significant neurological sequelae in later childhood. But the study did not specifically look at "alternative vaccine schedules" such as those proposed by alternative doctors. It also did not specifically look at vaccination outside the first year of life. It did however divide the children into "most timely" and "least timely" groups too look for effects that might be missed in aggregate.
This is a strong study. It seems likely that if vaccines given according to the recommended schedule during infancy were to lead to autism or other severe neurologic disorders, this study would have found an effect. Since autism usually manifests by age 2, it is unlikely that an exposure in the second or third year of life would contribute significantly to the development of autism. There is no such thing as "too many too soon"; it is simply another evidence-free attack on one of our safest and most effective public health measures.
Michael J. Smith, & Charles R. Woods (2010). On-time Vaccine Receipt in the First Year Does Not Adversely Affect Neuropsychological Outcomes Pediatrics, 125 (6), 1134-1141 : 10.1542/peds.2009-2489