New Research on the Timing of Vaccines and Neurodevelopmental Outcomes

Paul A. Offit, MD


July 21, 2010

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Hi, my name is Paul Offit. I am the Director of the Vaccine Education Center and Chief of the Division of Infectious Diseases here at Children's Hospital, Philadelphia [Pennsylvania]. Today, I want to talk about a paper by Michael Smith and Charles Woods that was published in the June issue of Pediatrics[1] that looked at the relationship between the timing of vaccines and outcomes, specifically neurologic and neurodevelopmental outcomes.

This paper can be tremendously useful to clinicians and actually was based on a study that had been done before that by Bill Thompson and colleagues at the CDC [US Centers for Disease Control and Prevention].[2] They wanted to see whether there was any relationship between receipt of thimerosal, an ethyl mercury-containing preservative that was in vaccines, and outcomes -- specifically, neurodevelopmental outcomes and autism.

They looked at more than 1000 children, who at this point were about 7 years old, and then tried to determine by looking at medical records exactly how much ethyl mercury or thimerosal they had received either in RhoGAM prenatally or in vaccines postnatally. Then prospectively, they did a series of 42 neurologic and psychological tests to see whether there was any relationship between receipt of thimerosal in vaccines and neurologic outcome, and what they found was, not surprisingly, that there was no relationship between receipt of thimerosal and autism or other neurodevelopmental problems.

What Michael Smith and Charles Woods did that I think was really interesting is they mined that dataset to see whether there was any relationship between the timing of receipt of vaccines and neurologic outcome. They divided these children into 2 groups. The first group were children who had received vaccines according to the CDC-AAP [American Academy of Pediatrics] schedule, and the second group were children whose parents had chosen to delay vaccines or not to give vaccines. What they found was that there was no difference between these 2 groups in terms of their neurologic outcomes.

I think that parents can be reassured here that a choice to delay vaccines or not to give vaccines does not in any sense decrease the risk for a poor neurologic outcome or autism; all it does is increase the period of time during which children are susceptible to vaccine-preventable diseases. Delaying vaccines or separating vaccines or withholding vaccines offers no benefit, and only increases the risk to the child. I think it would be of value for doctors to read this study and to share it with parents who are concerned about vaccines.

Thanks for your attention. Again, I am Paul Offit from the Vaccine Education Center here at Children's Hospital, Philadelphia. If you are interested in more information about vaccines or vaccine safety, please check our Website at Children's Hospital of Philadelphia.


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