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A critical federal vaccine panel has recommended against seasonal influenza vaccines containing a specific preservative – a change likely to send shock through the global medical and scientific community and possibly impact future vaccine availability.
The panel was unilaterally remade by health secretary Robert F Kennedy Jr, a vaccine skeptic who has urged against the use of thimerosal despite a lack of evidence of real-world harm.
Across three votes, members voted in favor of restricting thimerosal in seasonal influenza vaccines across all age groups – with five in favor of the restriction, one abstention and one vote against.
“The risk from influenza is so much greater than the nonexistent – as far as we know – risk from thimerosal,” said Dr Cody Meissner, a panel member and professor of pediatrics at Dartmouth’s Geisel School of Medicine who was the lone “no” vote.
“I would hate for a person not to receive the influenza vaccine because the only availability preparation contains thimerosal – I find that very hard to justify.”
The panel, formally called the Advisory Committee for Immunization Practices (ACIP) of the Centers for Disease Control and Prevention (CDC), is a critical link in the vaccine distribution pipeline – informing health insurers and clinicians alike about which vaccines to give patients.
Kennedy fired all 17 former members of the panel in June, citing conflicts of interest, and appointed eight new members, all of whom are ideological allies of the secretary.
None of the new members have published written conflict of interest disclosures or been added to a Trump administration-developed conflict of interest tracker for ACIP members, as of Thursday morning.
“There is a very big difference between what was shared at the meeting versus what is reality,” said Dr Sean O’Leary, chair of the American Academy of Pediatrics Committee on Infectious Diseases. “The science on thimerosal is settled, and the rhetoric being used to suggest otherwise is misleading and harmful.”
Rather than vote on an agenda that had once included seasonal recommendations for Covid-19 and the vaccine against human papilloma virus (HPV), ACIP added the controversial focus of thimerosal in vaccines. The panel affirmed that the influenza vaccine is recommended for Americans older than six months.
Although multiple studies have found no real-world harm, the preservative has been a talking point of anti-vaccine advocates for decades. Multiple representatives of physicians associations urged the panel to reject the recommendation against thimerosal in the meeting.
Thimerosal is used in about 5% of multidose seasonal influenza vials, and is known to be more cost effective than single-dose formulations. It is unclear how the vote will impact flu vaccine availability before the upcoming flu season, particularly for clinics that rely on such formulations.
Thimerosal has been used as a preservative in vaccines since before the second world war. In the early 2000s, thimerosal was removed from all routine pediatric and most adult vaccines as a precautionary measure – a decision that was criticized by experts who argued it sent mixed messages about a preservative that had not been found to cause harm. The issue has since been considered settled by mainstream medicine.
Thimerosal is an ethylmercury-based preservative. Ethylmercury is different from the kind of mercury found in seafood, called methylmercury. Ethylmercury has a much shorter half-life in the blood and brain, about seven days and 30 days respectively, compared to methylmercury, which has an approximately 44-58 day half-life and accumulates in the brain. The amount of ethylmercury contained in a flu vaccine (25 micrograms) is about half of that contained in a 3-ounce serving of canned tuna fish (40 micrograms).
Repeated, large studies conducted across several countries have found no association between thimerosal and neurological effects. A presentation from CDC career scientists that was initially expected to go through some of this substantial data was removed before the panel reconvened on Thursday.
In response to a question about the slapped down presentation, ACIP member Dr Robert Malone, a well-known anti-vaccine activist, said: “That article was not authorized by the office of the secretary and was removed.”
The panel instead heard a presentation from Lyn Redwood, a nurse practitioner who founded the World Mercury Project, the predecessor to Kennedy’s anti-vaccine advocacy group Children’s Health Defense. Prior to the meeting, her presentation was found to include a reference to a study that appeared to be made up.
“This is an old issue that has been addressed in the past and there are many issues we could discuss,” said Meissner.
Responding to criticism of Redwood’s presentation, ACIP chair Dr Martin Kulldorff, a former Harvard professor who was fired for refusing the Covid-19 vaccine, said: “It’s inappropriate to dismiss a presentation just because the person does not have a PhD or MD.”
The decision from ACIP could have global implications, because vaccines used around the world rely on thimerosal as a preservative in multidose vials, which are less expensive.
“I know ACIP is focused on the US, but recommendations that the ACIP makes are followed among many countries around the world,” said Meissner.
“Removing thimerosal from all vaccines used in other countries, for example, is going to reduce access to these vaccines, it will increase costs, and I think it’s important to note that no study has ever indicated any harm from thimerosal.”
