Now that the thimerosal-autism link has been thoroughly discredited, some autism advocates argue that neurodevelopmental problems are caused by overloading children's immune systems with too many vaccines too early in life. As a result, a growing number of parents are asking pediatricians to use alternative vaccination schedules that spread out the shots, even though there is no evidence to suggest that the practice may be helpful. In fact, common sense suggests that it is more likely to be harmful because the highest incidence of infection and mortality from pertussis, for example, occurs in the first six months of life. Failure to vaccinate also exposes other children in the community to infectious diseases that they might otherwise avoid.
Researchers cannot ethically conduct a clinical trial of delayed vaccinations because of the potential risks to the children involved. In an effort to circumvent this problem, pediatric infectious disease specialists Dr. Michael J. Smith and Dr. Charles R. Woods, both of the University of Louisville School of Medicine, analyzed data on 1,047 children enrolled in a previous study designed to determine whether thimerosal produced an autism risk. The children were born between 1993 and 1997, vaccinated by their parents on a schedule of the parents' choosing, and then subjected to a series of 42 neuropsychological tests between the ages of 7 and 10.
Just under half of the children (491 or 47%) received their vaccines on a timely basis, within 30 days of schedule. An additional 235 (23%) received all vaccinations, but not on schedule, and the remaining children received some but not all vaccines. On-time vaccination was most likely to occur among households in which the mother was highly educated and in which household income was higher.
The Louisville duo reported Monday in the journal Pediatrics that delayed vaccinations did not improve outcomes. In fact, outcomes in this group might have been worse. The researchers found that children vaccinated on time performed higher on 15 of the 42 tests than those who were not vaccinated on time. The latter group did not perform higher on any test. The researchers did not offer a potential explanation for this finding, but it may be linked to the higher household incomes.
Current vaccination schedules call for even more shots, so the results are not directly translatable, the authors conceded. But even with the added shots on the new schedule, children are actually exposed to lower doses of antigens because of improvements in the vaccines, they said, so the safety should remain the same.
"This study provides the strongest clinical outcomes evidence to date that on-time receipt of vaccines during infancy has no adverse effect on neurodevelopmental outcomes 7 to 10 years later," the authors wrote. "These results offer reassuring information that physicians and public health officials may use to communicate with parents who are concerned that children receive too many vaccines too soon."
The study was funded internally at the university. Woods has received honoraria from pharmaceutical companies for speeches and has received research funding from them for other projects.
-- Thomas H. Maugh II
Photo credit: Anacleto Rapping / Los Angeles Times