A new report from the U.S. Centers for Disease Control and Prevention (CDC) delivers a clear message: existing evidence does not support a link between thimerosal-containing vaccines and autism or other neurodevelopmental disorders. This finding, released ahead of a significant meeting of the CDC’s vaccine expert panel, aligns with the long-standing scientific consensus on vaccine safety.
The report reviewed existing studies on vaccines containing thimerosal, a mercury-based preservative historically used in multi-dose vials of vaccines and medicines to prevent contamination by germs like bacteria and fungi. While thimerosal has been largely phased out of childhood vaccines in the U.S., it is still present in some multi-dose influenza vaccine formulations for adolescents and adults.
Data from the CDC report indicates that during the most recent 2024-2025 flu season, an overwhelming 96% of all influenza vaccines administered in the United States were thimerosal-free. The report also noted a significant decrease over time in the use of thimerosal-containing flu vaccines among pregnant women, with only 0.3% of doses given to this group in 2024 containing the preservative.
Controversy Brews Ahead of Key Vaccine Meeting
The release of the CDC report coincides with heightened attention surrounding the upcoming meeting of the CDC’s Advisory Committee on Immunization Practices (ACIP). This meeting is the first since Health and Human Services Secretary Robert F. Kennedy Jr. controversially dismissed all 17 previous members and appointed a smaller, new panel, some of whom have publicly expressed vaccine-critical views.
One point of contention involved a presentation slated for the meeting by Lyn Redwood, a former leader of the anti-vaccine group Children’s Health Defense, founded by RFK Jr. Her presentation on thimerosal was initially posted on the CDC website and included a citation to a supposedly non-existent study by Professor Emeritus Robert Berman. Berman himself stated the cited study “does not exist” and that his actual research on a similar topic, published in a different journal, reached different conclusions. He explicitly stated he did “not endorse this misrepresentation.” Following Reuters’ reporting on the inaccuracy, the CDC uploaded a revised version of Redwood’s presentation, removing the slide with the erroneous citation.
The summary of Redwood’s presentation suggested advocating for the exclusive use of thimerosal-free flu shots for vulnerable populations, contrasting sharply with the CDC staff report finding no evidence linking thimerosal to harm beyond minor injection site reactions.
RFK Jr.’s Influence and Debunked Claims
Secretary Kennedy’s actions concerning the ACIP panel composition and his public stance on vaccines have drawn criticism. A long-time anti-vaccine activist, Kennedy has repeatedly promoted the false claim that thimerosal is “toxic to brain tissue” and causes autism, notably in his 2014 book. This assertion flies in the face of decades of extensive scientific research.
Numerous large-scale epidemiological studies from multiple countries, along with meta-analyses from leading health organizations like the WHO and the National Academy of Medicine, have consistently found no credible association between vaccines (including the MMR vaccine) or vaccine ingredients like thimerosal and autism spectrum disorder (ASD). Scientists point out that autism rates continued to rise even after thimerosal was removed from most vaccines in the U.S.
Experts emphasize that the increase in identified autism cases seen in recent CDC studies is attributed to improved screening methods and expanded diagnostic criteria, not an actual rise in prevalence or a link to vaccines. Mischaracterizing this as an “autism epidemic,” as Kennedy has done, is seen by many as stigmatizing and misleading. Critics also express concern about a new autism study announced by Kennedy, to be led by a controversial figure known for promoting discredited vaccine theories.
Calls for Meeting Delay Amid Concerns
The swift changes to the ACIP panel and the controversies surrounding the meeting agenda have prompted calls for postponement. Both Republican Senator Bill Cassidy and Democratic Senator Patty Murray, leaders on the Senate HELP Committee, have urged delaying the June 25-26 meeting, citing concerns about the smaller panel’s composition and the current vacancy in the CDC Director position. With no confirmed Director, Secretary Kennedy has effectively been making final recommendations, raising fears among critics that the ACIP meeting’s outcomes could reflect his personal agenda rather than independent scientific consensus.
Despite these concerns, the meeting agenda is set to include discussions and potential votes on recommendations for several vaccines, including maternal and pediatric RSV vaccines, influenza vaccines (specifically addressing thimerosal), COVID-19 vaccines, and the MMRV vaccine in young children. Experts like Dr. Paul Offit anticipate the new ACIP might recommend removing thimerosal from all vaccines, viewing this as a move that aligns with Kennedy’s agenda, potentially reducing vaccine availability without increasing safety, and fueling vaccine hesitancy.
