An expert committee that advises the centers for the control and prevention of diseases on vaccines met for the first time since the Secretary of Health, Robert F. Kennedy Jr., abruptly replaced the 17 members of the committee for eight carefully selected, on June 11, 2025.
The Committee, called Advisory Committee on Immunization Practices, generally debate and votes recommendations for specific vaccines. For this meeting, which will be held on June 25 and 26, 2025, discussions on COVID-19, Human Papillomavirus, influenza and other infectious diseases were scheduled.
However, according to an updated agenda, the Committee also plans to listen to a presentation on a chemical called Timerosal and vote on the recommendations proposed for use in influenza vaccines.
Public Health Experts have expressed concern about this presentation and point out that the defenders of anti -vacuum positions continue to promote confusion regarding the alleged health risks of the thimerosal, despite the broad investigations that demonstrate their safety.
I am a pharmaceutical and expert in pharmacological information, with 35 years of experience critically evaluating the safety and efficacy of medicines in clinical trials. There is no evidence that supports the idea that the timerosal, used as a preservative in vaccines, whether insecure or represents some health risk.
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What is the Timerosal?
Timerosal, also known as Tiomersal, is a preservative that has been used in some pharmaceutical products since the 1930s, because it prevents contamination by eliminating microbes and avoiding its proliferation.
In the human body, the thimerosal is metabolized and transforms into ethylmercury, an organic derivative of mercury. Studies in babies have shown that ethylmercury is quickly eliminated from blood. Often, ethylmercury is confused with methylmercury.
The latter is known for its toxicity and is associated with various negative effects in brain development, even at low levels of exposure. Environmental researchers identified the neurotoxic effects of mercury in children in the 1970s, mainly as a result of exposure to methylmercury present in fish.
In the 1990s, the Environmental Protection Agency (EPA) and the Food and Medicines Administration (FDA) established maximum recommended exposure limits to methylmercury, especially for children, pregnant women and women of fertile age.
Why is the timerosal controversial?
The fears on the safety of the thymusal in vaccines have spread for two reasons.
First, in 1998, a report was published – today discredited – in the prestigious medical magazine The Lancet. In it, British doctor Andrew Wakefield described eight children who developed autism after receiving the triple viral vaccine (MMR), which protects against measles, papers and rubella.
However, patients were not compared to a vaccinated control group, so it was impossible to draw valid conclusions about the effects of the vaccine. In addition, it was subsequently discovered that the report contained false data.
It should be noted that the MMR vaccine received by the children mentioned in that study never contained timerosal.
Second, federal guidelines on the limits of exposure to methylmercury were published approximately at the same time as Wakefield’s study. In that period, autism began to recognize itself more widely as a developmental disorder, and diagnostic rates were increasing.
Some mistakenly interpreted Wakefield’s results and confused methylmercury with ethylmercury, promoting the unfounded idea that ethylmercury present in the thimerosal was responsible for the increase in autism cases.
Wakefield’s study was retracted in 2010, and Wakefield was declared guilty of dishonesty and breach of ethical protocols by the General Medical Council of the United Kingdom, in addition to being stripped of his medical license.
Subsequent studies have not demonstrated any relationship between the MMR vaccine and autism. However, despite the absence of evidence, belief was rooted and has been difficult to eradicate.
Have scientists proved if the thimerosal is safe?
To date, no impartial research has identified toxicity caused by ethylmercury present in vaccines, nor has a link between this substance and autism or other development problems been found. And this is not due to a lack of studies.
A review carried out in 1999 by the Food and Medicines Administration (FDA), in response to federal guidelines to limit exposure to mercury, did not find evidence of damage caused by the thimerosal as a preservative in vaccines, except for some rare allergic reactions.
Even so, as a precautionary measure of concern for exposure to mercury in babies, the American Pediatrics Academy and the United States Public Health Service issued a joint statement in 1999 recommending to eliminate the bervery from vaccines.
At that time, only a children’s vaccine was available in a version containing timerosal: the DTP vaccine, against diphtheria, tetanus and whore cough. The other children’s vaccines were already available only in formulations without thimerosal or had versions without such component.
For 2001, manufacturers in the United States had eliminated the thymusal of almost all vaccines, including all of the children’s vaccination calendar.
In 2004, the Committee for the Safety of Immunizations of the US Institute of Medicine.
Additional, rigorous and independent studies, reviewed by the CDC and the FDA, did not find a relationship between thimerosal and autism or with delays in neuropsychological development.
How is Timerosal used today?
In the United States, most vaccines are currently in roads or monodosis syringes. Timerosal is only found in some multidosis vials used in large -scale immunization campaigns, specifically in a small number of influenza vaccines.
It is not added to modern children’s vaccines, and those who are vaccinated against the flu can avoid the thimerosal requesting a vaccine in monodosis presentation.
Timerosal is still used in some vaccines in other countries to guarantee continuous access to essential vaccination programs. The World Health Organization argues that there is no evidence of toxicity in babies, children or adults exposed to vaccines that contain timerosal.
This article was originally published in The Conversation
See: CDCS report reveals that beamerosal in vaccines is not linked to the development of autism
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