What is thimerosal, the flu vaccine ingredient targeted by RFK Jr.?

Yahoo

19 hours ago

Federal vaccine advisers installed by Health and Human Services Secretary Robert F. Kennedy Jr. voted Thursday to stop recommending influenza vaccines containing thimerosal, a preservative that has been long criticized by anti-vaccine activists.
Scientists and public health authorities have deemed thimerosal safe, and the vast majority of flu shots don't have it. But the removal would probably make flu vaccines more expensive and harder to receive for some Americans, public health experts said.
Subscribe to The Post Most newsletter for the most important and interesting stories from The Washington Post.
Medical experts say the move is the latest by Kennedy, who was a longtime anti-vaccine activist before he joined the Trump administration, to chip away at vaccine policies. Here's what to know about thimerosal:
- - -
What is thimerosal?
Thimerosal, which the Food and Drug Administration describes as a 'mercury-containing organic compound,' is used as a preservative in vaccines to stop microbial growth and prevent contamination. Since 2001, all childhood vaccines licensed and recommended in the United States have been thimerosal-free, with the exception of some multi-dose formulations of flu vaccines.
When used in vaccines, it is metabolized into ethylmercury in the body, which is vastly different from methylmercury, which can be found in fish. The levels of ethylmercury in vaccines have been found to be safe, while high levels of methylmercury can cause childhood developmental damage, medical experts and the U.S. government says.
'There is a robust body of peer-reviewed, scientific studies conducted in the United States and countries around the world that support the safety of thimerosal-containing vaccines,' the FDA writes on its website.
The Centers for Disease Control and Prevention posted a 17-page document online this week saying thimerosal was safe. That document was intended to be background material for members of the Advisory Committee on Immunization Practices before its meeting and vote, according to a federal health official familiar with the document. But it was posted on the ACIP website, and then removed Wednesday.
'This document by the CDC vaccine safety office did not go through the appropriate process to be posted,' an HHS spokesperson told The Washington Post.
- - -
Why is thimerosal controversial?
In the 1990s, amid suspicion thimerosal could be a cause behind the rising rates of autism, the U.S. Public Health Service and the American Academy of Pediatrics recommended thimerosal be removed from vaccines out of an abundance of caution and to restore public confidence. By the early 2000s, thimerosal had been removed or reduced to trace amounts in most childhood vaccines, with manufacturers increasingly using single-dose vials that did not require preservatives.
Several studies have shown that there is no link between thimerosal and autism.
'There is no evidence to suggest that the amount of [thimerosal] used in vaccines poses a health risk,' according to the World Health Organization, which says other medical groups in the U.S. and Europe hold the same views.
After thimerosal was removed from most childhood vaccines, autism rates have continued to rise.
- - -
What is the impact of removing thimerosal?
It would be limited.
In the most recent flu season, 94 percent of all influenza vaccines administered in U.S. were thimerosal free, according to the CDC. The rate was even higher for shots administered through two major government vaccine programs.
Multi-dose vials are easier to store and use for large vaccine fairs than the single-dose counterparts. They're also less expensive, reducing waste and requiring less space to store. Public health experts said medical facilities targeted at rural areas and safety net systems could face potential shortages if they remove those vaccines, although an FDA representative at the meeting said there would be enough supply to make up for the shortfall.
- - -
What has Kennedy said about thimerosal?
Before the meeting on Tuesday, Kennedy decried the description of thimerosal as safe, writing on X that 'I leave it to the reader to speculate as to why CDC has not performed such studies in the intervening 24 years as it dosed hundreds of millions of American children and pregnant moms with mercury-laden flu shots.'
On his social media post, he cited several studies he said supported his claims - and contradicted his own agencies. Medical experts told The Post that Kennedy was misstating the science.
'It's a way to overwhelm an audience who mostly WON'T click each one to find what they are looking for,' said Jessica Malaty Rivera, an infectious-disease epidemiologist, in a text. 'Second, there is zero evidence of his claims in any of those links.'
In 2015, Kennedy edited a book titled 'Thimerosal: Let the Science Speak' in which he wrote 'the evidence of thimerosal's neurotoxicity is so overwhelming and the lack of any safety data so complete that anyone who is willing to read science and who believes in the capacity for scientific methods to determine empirical truths must conclude that thimerosal causes serious brain damage.'
He also noted in his introduction that he 'assembled this book' to persuade the CDC to get rid of thimerosal in any vaccines.
In a speaking appearance in April 2023 challenging coronavirus mandates, Kennedy pointed to his book, calling it 'definitive' proof that thimerosal 'is the cause of all these neurological injuries.'
He went on a podcast later that year, where he talked more about thimerosal.
'This particular kind of vaccine, the multi-dose vial, is going to children, little children, it's destroying their brains,' Kennedy said in a July 2023 podcast appearance. 'You can accept that or not, I'm telling you that that's my belief, and I believe my belief is strongly grounded in science.'
- - -
Caitlin Gilbert and Lena H. Sun contributed to this report.
Related Content
Dynamite outside a synagogue: Civil rights stories imperiled by federal cuts
In West Virginia, Medicaid is a lifeline. GOP cuts could devastate the state.
3-pound puppy left in trash is rescued, now thriving