I was still on leave during the now-infamous Tylenol press conference in September, but one part of it seemed to slip under the radar: when President Trump called for getting aluminum out of vaccines.

Why it matters: A form of aluminum is used in many childhood vaccines to elicit a stronger immune response. Banning it would throw the entire vaccine ecosystem into disarray, but even less drastic restrictions on its use could be disruptive.

Driving the news: The CDC's vaccine advisory committee this week announced the creation of a working group to review the childhood vaccination schedule, including the timing and order of different vaccines and the safety of certain ingredients.

• An example topic for discussion, per the document, would be whether "either of the two different aluminum adjuvants increase the risk of asthma?"

The big picture: Vaccine skeptics, including Health Secretary Robert F. Kennedy Jr., have long questioned the scientific consensus that the small amount of aluminum used in vaccines is safe. Now, the federal government is poised to reopen the safety debate and potentially add guardrails.

• This could affect DTaP, hepatitis A and B, HPV, pneumococcal and meningococcal vaccines.
• "Previous scientific research has shown the amount of aluminum exposure in people who follow the recommended vaccine schedule is low and is not readily absorbed by the body," the CDC website states.

Flashback: Trump's aluminum mention last month was almost a throwaway line: "We want no mercury in the vaccine. We want no aluminum in the vaccine."

• In July, HHS adopted a recommendation from Kennedy's vaccine advisers to remove from all influenza shots a mercury preservative that anti-vaccine activists have long suggested is linked to autism.
• Anti-vaccine advocates have also claimed aluminum in vaccines is unsafe.
• Over the summer, Kennedy took the unusual step of calling for the retraction of a Danish study that found no link between aluminum in vaccines and chronic disease in children, but was rebuffed.

State of play: "What's likely what is going to happen, I speculate, is at some point that subcommittee is going to take a look at that question and they're going to come away saying there's a lot of evidence [aluminum] has some issues," Robert Malone, one of Kennedy's handpicked appointees on the CDC vaccine advisory committee, told me.

• The question that's within the committee's purview, he said, is whether the CDC should continue recommending vaccines with aluminum in them, scrap the current recommendation or essentially require a prescription for the shots by advising "joint decision-making" with a doctor.
• "The probability, I would speculate, is they would place it under the category of joint decision-making," Malone told me.
• "Bobby's position has been he doesn't want to take anybody's vaccine away," he added.

Yes, but: While recommending that the public consult with doctors before getting these common vaccines would add a barrier to access, it's certainly not the same thing that Trump called for last month.

• "Trump out-Kennedyed Kennedy," Malone said, quoting ex-Trump advisor Steve Bannon. "The president feels very strongly about these issues, and maybe even more strongly than the secretary does."

Go deeper ...

Mainstream scientific experts have begun sounding the alarm over Kennedy and his allies' focus on aluminum.

• Of course, the CDC and its advisory committee aren't the only tools Trump or Kennedy have at their disposal should they want to make big changes.

What they're saying: The biggest damage that could be done is via litigation, pediatrician and vaccine expert Paul Offit recently wrote on his Substack.

• "Sometime in the next couple of months, Kennedy will hold up a bogus 'study' that he will claim proves that aluminum adjuvants in vaccines cause autism or some other chronic disorder," Offit said.
• "Although the 'study' won't have been published in a reputable journal, won't have been peer-reviewed, will be methodologically flawed and basically uninterpretable, he will call it 'landmark' or 'gold-standard' ..."
• "Then he will manipulate the [National Vaccine Injury Compensation Program] to make vaccines less available, more expensive, and more feared."

The VICP is the program created by statute through which people with vaccine injuries can get legal recourse. If more conditions are deemed vaccine injuries and made eligible for compensation, the program's budget would likely get blown up.

• And if vaccine manufacturers end up being more directly liable for vaccine injury claims, it could ultimately spook them out of participating in the U.S. market.

"I believe he's going to claim in his autism report that there's an association between [aluminum] ... and autism, which is going to set in place a litigation enterprise against the vaccines and potentially bankrupt the Vaccine Injury Compensation Program," former FDA commissioner and Pfizer board member Scott Gottlieb recently told CNBC.

• "So that could take down the whole pediatric vaccine enterprise," he added. "There's no good alternative [to aluminum]. It could force the vaccine manufacturers to try to reformulate the vaccines."