Robert F Kennedy Jr, the man Donald Trump has nominated to oversee key US health agencies, rose to national prominence as one of the most persistent and influential vaccine deniers in the country.

Kennedy, 70, backed Trump after ending his own third-party bid for president in August. He is the son of the former attorney general and presidential candidate Robert F Kennedy and the nephew of president John F Kennedy.

Trained as an environmental lawyer, RFK Jr gained notoriety for spreading conspiracy theories and questioning scientific research – often positioning himself as someone who is better qualified than scientists to understand diseases and epidemiology.

He has amplified unfounded claims that vaccines are tied to autism in children, promoted the false idea HIV is not the cause of Aids and baselessly linked certain antidepressants to a rise in school shootings, and the use of a certain herbicide to a rise in young people coming out as transgender.

A 2019 study found that Kennedy’s organisation was one of the top two funders of anti-vaccine ads on Facebook. In 2021, the Center for Countering Digital Hate named him as one of the top 12 spreaders of online misinformation about the Covid-19 vaccine.

Notably, Kennedy’s Children’s Health Defense, the nonprofit anti-vaccine group he led until becoming a presidential candidate, flooded American Samoa with vaccine misinformation ahead of a devastating measles outbreak there in 2019.

The position to lead the US health department needs Senate approval. If approved, experts say vaccines will be “the first issue on the table”.

Dr Michael Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said even if public policies remain unchanged, should authorities with the imprimatur of the federal government speak out against vaccines, “that discourages people who might otherwise be vaccinated, and at that point that’s as bad as not having a vaccine at all”.

The effects are not theoretical. As recently as last week the Centers for Disease Control and Prevention (CDC) released a report that found fewer than one in six healthcare workers had received updated Covid-19 vaccines in the 2023-24 respiratory virus season, and under half had received flu shots.

Childhood vaccinations have also dipped since the pandemic. Vaccination hesitancy and misinformation were both cited as major reasons by researchers.

“We forget what this country was like 50 years ago – how many children died every year from polio, pertussis [whooping cough], measles,” said Osterholm. “We’re going to see the return of diseases we have controlled for decades.”

RFK Jr has also recommended removing fluoride from drinking water, although fluoride levels are mandated by state and local governments.

He has pushed against processed foods and the use of herbicides like Roundup and has long criticised the large commercial farms and animal feeding operations that dominate the industry.

He wants to end the “revolving door” of employees who have previous history working for pharmaceutical companies or who leave government service to work for that industry.

He also wants to fire 600 employees at the National Institutes of Health, which oversees vaccine research, and replace them with 600 new workers.