On July 1, Georgian– and Russian-language Facebook users shared a clip from an interview between Robert F. Kennedy Jr. and Tucker Carlson. According to Kennedy, the U.S. Centers for Disease Control and Prevention (CDC) concealed the results of a 1999 study which allegedly showed that the risk of autism increased by 1135% after receiving the hepatitis B vaccine.
Kennedy’s claims about the hepatitis B vaccine are not true. The study in question was related to the safety of thimerosal-containing vaccines and not specifically to the hepatitis B vaccine. The study did not confirm that the risk of autism increased following vaccination. There is no evidence that the U.S. Centers for Disease Control and Prevention hid or altered the results of the study.
According to the fact-checking service Factcheck.org, Kennedy has made these claims in several interviews, but the study he references does not support his statements. The vaccine safety study, led by Thomas Verstraeten, was conducted through observations of children born between 1992 and 1999. The two-phase study was published in 2001 and aimed to assess the safety of vaccines containing thimerosal. Thimerosal is a mercury-based preservative that had been used in vaccines in the U.S. for years. The U.S. Food and Drug Administration (FDA) found no evidence of harmful effects from thimerosal in vaccines, but as a precautionary measure, it was removed from routine childhood vaccines in 2001.
According to Verstraeten’s study, there was no consistent link found between thimerosal-containing vaccines and neurodevelopmental disorders. The study did observe conflicting results in some cases, which is why the article states that further research in this area is necessary.
Kennedy claims that the preliminary results of the study showed a strong link between vaccines and autism, and that these results were later suppressed. However, it is important to note that the study clearly states that different phases yielded different results. In the first phase, a link was found with tics and speech delays (not autism), while in the second phase no such associations were found. The study also notes that no increased risk for autism or attention deficit disorder was found at any stage.
In an additional explanatory note related to the study, Verstraeten writes that the main conclusion of the research was the need for continued study in this direction. He explains that there is a common misconception that an epidemiological study can only yield two outcomes, either positive or negative – in this particular case, to either confirm or deny a link between vaccines and autism. However, there is often a third possibility: a neutral outcome, where no link is either confirmed or denied. According to Verstraeten, this is what occurred in the thimerosal study. Initially, the results were seen as positive – phase one showed a connection between vaccines and neurological disorders, which, as already mentioned, is clearly written in the published study. But in the second phase, those results were not replicated – meaning the connection was not confirmed. Due to the conflicting results, the study neither confirmed nor denied a link between thimerosal and neurological disorders; therefore, in the conclusion of the study, it is recommended to conduct further research.
Factcheck.org notes that the CDC held a meeting to discuss the phase one results, which Kennedy portrays as an attempt to cover up the findings. However, according to the publication, the data presented at the meeting did not show a significant association between thimerosal and autism. In fact, after the meeting, the specialists concluded that it was not possible to rule out a connection between neurodevelopmental disorders and thimerosal. This led to the second phase of the study, which did not find any significant link between thimerosal-containing vaccines and autism or other neurodevelopmental conditions, as is also evident in the published article.
In the explanatory note, Verstraeten writes that the study was planned to be two-phase from the beginning, but since the results from the first phase could have had significant implications for health policy, rapid validation of the findings was necessary. Verstraeten denies that the CDC designed the second phase in a way that would contradict the first. He explains that because the second phase did not replicate the first phase’s findings, the study’s conclusion shifted from “positive” to “neutral” – the harmful effects of thimerosal were not confirmed, and further research was recommended.
The statistic cited by Kennedy that the hepatitis B vaccine increased autism risk by 1135% is also not confirmed by Verstraeten’s studies. According to Factcheck.org, this figure appears in a presentation by the anti-vaccine group SafeMinds. The group claimed it obtained early results of Verstraeten’s study through the Freedom of Information Act, but it has not published the documents on which its claims are based.
Anti-vaccine individuals often spread false information claiming that thimerosal in vaccines is harmful and causes autism, which is not supported by scientific studies.
In general, the claim that vaccines cause autism is one of the most persistent myths about vaccination. The world’s leading medical organizations, based on scientific research, assert that there is no link between vaccination and the development of autism spectrum disorders. Current research suggests that autism spectrum disorders cannot be explained by a single cause but are probably due to a combination of genetic, developmental, and environmental factors.
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