- In 1991, the Centers for Disease Control and Prevention (CDC) recommended the hepatitis B vaccine for all newborns to protect against serious liver infections.
- However, concerns have been raised about its safety, particularly a potential link to autism.
- Researchers analyzed data from the National Health Interview Survey (1997-2002) to explore the relationship between hepatitis B vaccination and autism diagnoses in boys aged three to 17.
- The study focused on a time when thimerosal, a mercury-based preservative, was still used in some vaccines.
- It found that boys vaccinated as newborns had a three-fold higher likelihood of being diagnosed with autism compared to those vaccinated later (after the first month of life) or not at all. Non-Hispanic white boys and boys from two-parent households were significantly (70 percent) less likely to be diagnosed.
In 1991, the Centers for Disease Control and Prevention (CDC) recommended that all newborns in the United States receive the hepatitis B vaccine to prevent liver infection that can lead to long-term health complications. However, over time, concerns have emerged regarding the vaccine’s safety, particularly its potential link to autism.
A study published in the Journal of Toxicology and Environmental Health, Part A examined the issue by analyzing data from the National Health Interview Survey (NHIS) between 1997 and 2002. The large government survey collects information from U.S. households to track medical trends and public health concerns.
Researchers focused on boys aged three to 17 years born before 1999, when some vaccines still contained a mercury-based preservative called thimerosal, to determine whether early hepatitis B vaccination was associated with an increased risk of autism.
The study analyzed data from nearly 80,000 children, including 193 diagnosed with autism. Key findings include:
- 4.3 out of every 1,000 boys were diagnosed with autism.
- 29 percent of boys with autism had received the hepatitis B vaccine within the first month of life, compared to 17 percent of boys without autism.
- Non-Hispanic white boys made up 48 percent of the autism group and 59 percent of the non-autism group, indicating autism was somewhat more common in non-white boys.
- None of the Asian boys in the study who received the vaccine at birth were diagnosed with autism.
- 58 percent of boys with autism lived in two-parent households, compared to 71 percent of boys without autism.
- 75 percent of boys with autism had mothers with at least a high school education, similar to the 78 percent of boys without autism.
When researchers ran statistical analyses to compare different factors, they found that:
- Boys vaccinated at birth had nearly three times the odds of an autism diagnosis compared to those vaccinated later or not at all.
- White boys were 64 percent less likely to be diagnosed with autism than non-white boys.
- Boys from two-parent households were 70 percent less likely to be diagnosed with autism than boys from single-parent households.
- Boys with mothers who had at least a high school education appeared twice as likely to be diagnosed with autism, though this result was not statistically significant.
Even after adjusting for race, family background and maternal education, the association between early hepatitis B vaccination and autism remained. This study found that boys born before 1999 who received the hepatitis B vaccine within their first month of life were more likely to be diagnosed with autism than those vaccinated later or not at all. Notably, the study found no similar association in girls. However, since only a small number of girls in the study were diagnosed with autism, further research is needed to determine whether gender plays a role.
Some scientists caution that studies linking vaccination to autism may be influenced by selection bias. This occurs when children who see doctors more frequently – possibly due to preexisting health concerns – are both more likely to be vaccinated and more likely to receive an autism diagnosis.
To account for this possibility, researchers in this study examined whether hepatitis B vaccine was linked to unrelated health conditions like Down syndrome or heart defects. They also analyzed other childhood vaccines, such as MMR (measles-mumps-rubella) and varicella (chickenpox), to see if they were also associated with autism. Moreover, the study authors also considered whether children from two-parent households were both more likely to be vaccinated and more likely to be evaluated for autism. But due to inconclusive findings, researchers suggest that selection bias alone cannot explain the results.
Study limitations
This study had some important limitations:
- It could not test to determine whether a specific vaccine ingredient (like thimerosal or aluminum) contributed to the observed association.
- The data relied on parental reports of autism diagnosis, which may be less reliable or precise than medical records.
- It did not distinguish between different subtypes of autism, such as Asperger’s syndrome or autism with co-occurring health conditions.
- The overall autism rate in this study was lower than what other large studies have reported, possibly because children in urban areas – where autism diagnoses are more common – were underrepresented.
- Children without vaccination records were excluded, which could have affected the autism rate calculations.
While this study highlights a potential link between early hepatitis B vaccination and autism in boys, it does not establish causation. Ongoing research is essential to fully understand the long-term effects of vaccination to ensure children’s health and safety.
Watch Health Secretary Robert F. Kennedy Jr. making the case that the hepatitis B vaccine is largely responsible for the autism epidemic in this clip.
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