Vaccines that contain thimerosal, a common preservative, don’t cause negative social behaviors or brain changes in infant primates, a new study shows.
In the study, infant rhesus macaques received several pediatric vaccines containing thimerosal, a mercury-based preservative, in a schedule similar to that given to infants in the 1990s.
Other animals received just the measles-mumps-rubella (MMR) vaccine, which does not contain thimerosal, or an expanded vaccine schedule similar to that currently recommended for infants in the United States. Control animals received a saline injection.
Regardless of vaccination status, all animals developed normal social behaviors—the administration of vaccines to rhesus macaques did not result in neuropathological abnormalities or aberrant behaviors such as those often observed in autism.
Cellular analysis of the cerebellum, amygdala, and hippocampus—three brain regions known to be altered in autism—was similar in vaccinated and unvaccinated animals.
“This comprehensive study included many physiological measures and behavioral measures, says Gene Sackett, professor emeritus of psychology at the University of Washington.
“Fundamentally the vaccines had no ill effects. To the extent that macaques mirror human physiology, I think this bears out what most people have known: These vaccines are safe.”
Published in the Proceedings of the National Academy of Sciences, the study was designed to compare the safety of different vaccination schedules, including the schedule from the 1990s, when thimerosal was used as a preservative in multi-dose vaccine preparations, says Laura Hewitson of the Johnson Center for Child Health and Development.
Additional researchers from the University of Washington, the University of Texas Southwestern, and Texas A&M University are coauthors of the study.
Source: University of Washington