The lawyer helping Robert F. Kennedy Jr. pick federal health officials for the incoming Trump administration has petitioned the government to revoke its approval of the polio vaccine, which for decades has protected millions of people from a virus that can cause paralysis or death.

That campaign is just one front in the war that the lawyer, Aaron Siri, is waging against vaccines of all kinds.

Mr. Siri has also filed a petition seeking to pause the distribution of 13 other vaccines; challenged, and in some cases quashed, Covid vaccine mandates around the country; sued federal agencies for the disclosure of records related to vaccine approvals; and subjected prominent vaccine scientists to grueling videotaped depositions.

Much of Mr. Siri’s work — including the polio petition filed in 2022 — has been on behalf of the Informed Consent Action Network, a nonprofit whose founder is a close ally of Mr. Kennedy. Mr. Siri also represented Mr. Kennedy during his presidential campaign.

Mr. Kennedy, President-elect Donald J. Trump’s choice for health secretary, has said that he does not want to take away access to any vaccines. But as he prepares for his confirmation hearing and plans a fresh health agenda, his continuing close partnership with Mr. Siri suggests that vaccine policy will be under sharp scrutiny. It is a chilling prospect to many public health leaders, especially those who recall the deadly toll of some vaccine-mitigated diseases.

At the Trump transition headquarters in Florida, Mr. Siri has joined Mr. Kennedy in questioning and choosing candidates for top health positions, according to someone who observed the interactions but insisted on anonymity to disclose private conversations. They have asked candidates about their views of vaccines, the person said.

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