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Fact-Check: Claim Regarding Vaccine Impact on Baby Monkeys' Brain Development

What We Know

The claim suggests that baby monkeys vaccinated according to a standard vaccination schedule exhibited abnormalities in brain regions associated with social and emotional development. This assertion appears to stem from interpretations of studies involving rhesus macaques and their responses to vaccines, particularly the measles, mumps, rubella (MMR) vaccine and thimerosal-containing vaccines (TCVs).

A significant study published in the Proceedings of the National Academy of Sciences found that the administration of TCVs to infant rhesus macaques did not result in autism-like behaviors or neuropathological changes in critical brain regions such as the cerebellum, hippocampus, or amygdala (Gadad et al., 2015). The researchers observed no significant differences in social behaviors between vaccinated and control groups.
Another study examined the effects of the complete U.S. childhood vaccine schedule on amygdala growth in rhesus macaque infants. It reported that while there were differences in amygdala volume between vaccinated and unvaccinated groups, the findings did not conclusively link these changes to behavioral abnormalities associated with autism (Novella et al., 2011).
Additional research indicated that the administration of TCVs did not lead to brain or behavioral abnormalities similar to those observed in autism spectrum disorder (ASD) (Johnson Center for Child Health & Development).
The Institute of Medicine (IOM) has reviewed the safety of childhood vaccines multiple times and found insufficient evidence to support a connection between vaccines and developmental disorders (IOM, 2004).

Analysis

The claim that vaccinated baby monkeys exhibit brain abnormalities affecting social and emotional development is not supported by the majority of scientific evidence. The studies referenced in the claim do not provide robust evidence linking vaccination to the described outcomes.

The study by Gadad et al. (2015) is particularly significant as it specifically aimed to investigate the effects of TCVs and the MMR vaccine on infant macaques. The results showed no behavioral or neuropathological changes, directly contradicting the claim.
The findings regarding amygdala growth from the study by Novella et al. (2011) suggest some differences in brain structure; however, these differences do not imply a direct causative relationship with social or emotional deficits. The authors noted that the macaque model is relevant for studying environmental exposures but did not conclude that vaccines caused the observed changes.
The reliability of the sources is high, as they are peer-reviewed studies published in reputable journals. The studies were conducted by credible researchers in the field, and the methodologies employed were rigorous.
Furthermore, the interpretation of the findings in the claim lacks nuance and does not reflect the consensus in the scientific community, which largely agrees that there is no causal link between vaccines and autism or related developmental disorders.

Conclusion

The claim that baby monkeys vaccinated according to the standard schedule exhibited abnormalities in brain regions affecting social and emotional development is False. The available scientific evidence, particularly from studies involving rhesus macaques, demonstrates no significant behavioral or neuropathological changes attributable to vaccination. The consensus in the scientific community supports the safety of vaccines and their lack of association with autism or similar disorders.