U.S. Health Secretary Robert F. Kennedy Jr.’s newly appointed Advisory Committee on Immunization Practices (ACIP) upheld recommendations for the fall flu vaccination to be administered to anyone 6 months and older, as long as the shots are completely mercury-free.

While some Western Pennsylvania doctors say the new recommendations won’t change how the average person receives the flu shot, others say the outcome of Thursday’s debate sets a new precedent for health care.

“It’s a much more symbolic decision about what direction ACIP is headed in,” said Dr. Amesh Adalja, a Pittsburgh-based infectious disease specialist.

TribLIVE looked into the history of the flu vaccine and what this new recommendation means for the medical world.

What is influenza?

Influenza, or flu, is a highly infectious airborne disease that typically crops up seasonally. Symptoms of the flu can range in severity, with those infected experiencing fevers, chills, stomach problems and body aches. In extreme cases, the flu can lead to hospitalization or death, the National Institutes of Health said.

The U.S. has thousands of flu-related deaths a year, said Dr. Richard Zimmerman, a professor of medicine and public health at the University of Pittsburgh.

“I think it shows the need for vaccines,” Zimmerman said.

The flu’s origin

Early attempts to create a vaccine began in 1918 during the influenza pandemic, also known as the “Spanish Flu,” which killed an estimated 50 million people.

The flu came in two waves.

The first began in spring and had minimal deaths resulting from fevers spanning three days. The second phase took place in the fall and was much more severe, with some infected individuals dying within a few hours of their first symptoms, according to the National Archives.

While infections ran rampant in urban areas, it also spread to more rural areas, including remote parts of Alaska. A fifth of the world’s population was contaminated by the virus. Within just one year, the life expectancy rates in the U.S. dropped by 12 years, the archives said.

How has the flu vaccine been working?

For over a decade, the ACIP has recommended the annual flu vaccination for all persons ages 6 months and older, according to the Centers for Disease Control and Prevention.

“It’s hard to know what to expect with the ACIP as it’s currently constituted, but that has been the standing recommendation for several years now,” said Adalja, who is a senior scholar to Johns Hopkins University Center for Health Security. “I think it generally is a good one.”

Current flu vaccines contain three different strains of influenza, which are selected by doctors who monitor what strains are circulating toward the tail end of the prior flu season. These doctors then infer what flu strains will be going around for the upcoming season, he said.

What is thimerosal?

Thimerosal is a preservative found in the flu vaccine to help facilitate the use of multi-dose vials without the risk of contamination. It contains a particular type of mercury.

Kennedy has long been a proponent of a link between thimerosal and autism. However, there have been no studies showing evidence of the relation. In 2001, vaccinations for children under 7 years old must have thimerosal-free vaccines, as reported by The Associated Press.

Adalja said the type of mercury found in thimerosal is not toxic.

“What the antivaccine movement has done is they’ve conflated different types of mercury in an unwarranted manner,” he said.

Medical organizations around the U.S. have shared statements including the American Academy of Pediatrics and the American Medical Association.

Thimerosal is a preservative found in some flu vaccines. False information and faulty “science” about thimerosal are frequently used to mislead parents in an attempt to scare them out of vaccinating their children.

Here’s the truth: https://t.co/YF0aGwia8g pic.twitter.com/Vijqo33FLZ

— American Academy of Pediatrics (@AmerAcadPeds) June 26, 2025

Vaccines save lives. And in times like these, clear, evidence-based guidance matters more than ever. #OurAMA joins 79 medical societies to reaffirm that vaccines for flu, COVID-19 & RSV are vital to preventing serious illness. https://t.co/1ZSKAdiRPW #VaccinesWork

— AMA (@AmerMedicalAssn) June 25, 2025

A new precedent

Both Zimmerman and Adalja agree that those who choose to participate in the annual flu vaccine will not be negatively impacted by the removal of thimerosal.

“I don’t think this is a big deal,” Zimmerman said. “It does allow those who wish to say there’s no mercury at all in the vaccines.”

However, Adalja worries about what the 5-1 vote in favor of removing the preservative means for the future of the committee and does not believe the recommendation will ease the fears of people who are hesitant to trust vaccines.

“[The] ACIP vote to remove thimerosal based on basically zero evidence, and all the evidence regarding thimerosal is in favor of its safety … is a major precedent for ACIP becoming really a vehicle for antivaccine propaganda,” he said.

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