Dr Heidi Overton, Donald Trump’s nominee to lead the US Food and Drug Administration (FDA), has told senators the measles, mumps and rubella (MMR) vaccine is “safe and effective”, weeks after standing behind the president as he suggested the shot could be “quite lethal”.

At a confirmation hearing on Thursday, Overton described the MMR vaccine as “safe and effective”, adding: “It is our best tool right now in the public health response to the measles outbreak.”

Asked whether any vaccine on the US market was unsafe, she said: “Every vaccine on the US market right now is safe and effective according to the FDA.”

Overton faced questions from Bill Cassidy, the Louisiana Republican and physician who chairs the Senate health committee, whose vote is seen as pivotal. He had called her role in Trump’s August vaccine executive order “almost disqualifying”.

The hearing comes as the US records its highest number of measles cases since 1991.

When Cassidy asked what Overton would do if the president asked her to break those assurances on vaccine safety, she replied: “I would give him my best advice, and I would follow the statutory requirements for the role of FDA commissioner regarding individual product determinations for safety and efficacy.”

When Bernie Sanders, the independent Vermont senator, asked whether she would have “the courage to stand up to” a president who he said “lies all of the time”, Overton did not answer directly. “I have worked for the president for a long time now, and earned his trust because I have been part of robust discussions to bring him the best advice,” she said.

In her opening statement, Overton framed her agenda around speeding up drug development to protect US leadership in biotechnology. “We can protect America’s global leadership in biotechnology, but we have to act fast,” she said, pledging to make the FDA “the agency of the possible, rather than the impossible”.

Overton, whose father leads a church in her home town of Gallup, New Mexico, has described Colossians 3:23 (“Whatever you do, work at it with all your heart, as working for the Lord, not for human masters”) as one of her life verses since childhood.

Susan Collins, the Maine Republican senator, challenged her over the FDA’s August authorization of flavored vapes and nicotine pouches, including blueberry, mango and cappuccino. Collins said nearly 90% of young e-cigarette users choose flavored products.

Overton said there was “100% agreement from this administration that we must protect kids”, but defended the decision as recommended by career staff because “so many adults are using flavors preferentially”. She added: “If that standard is not appropriate, we should work on statutes to fix that.”

If confirmed, Overton, 37, would be the youngest ever FDA commissioner. A surgeon by training, she is now deputy assistant to the president for domestic policy, and served as a White House fellow during Trump’s first term.

In a February 2023 issue brief for the conservative America First Policy Institute, where she was chief policy officer, she criticized federal policies that allowed abortion pills to be sent through the mail, writing that abortion “is corrosive to children, women, and society broadly”.

She would replace Marty Makary, who resigned in May, and take over an agency still recovering from 2025 layoffs that cut its workforce by nearly 20%.