US President-elect Donald Trump said on Thursday that he had selected Robert F. Kennedy Jr., an environmental activist who has spread misinformation on vaccines, to lead the Department of Health and Human Services, the top health agency in the United States.

In a post on X, Kennedy vowed to work to end chronic diseases, clean up corruption and provide Americans with the data they needed to make informed decisions, vowing to Trump that he would work to "Make America Healthy Again”.

Kennedy ran for president in this year's election as an independent before dropping out in August and endorsing Trump, in exchange for a role in the Republican's administration.

"The Safety and Health of all Americans is the most important role of any Administration, and HHS will play a big role in helping ensure that everybody will be protected from harmful chemicals, pollutants, pesticides, pharmaceutical products, and food additives that have contributed to the overwhelming Health Crisis in this Country," Trump said in a post on social media.

The appointment, which had been seen as a possibility for weeks, raised concern among some public health advocates who said Kennedy could have a negative role in Americans' health given his power over public health agencies. The Democratic Party decried the decision.

Some politicians and business groups supported the nomination, such as the National Community Pharmacists Association, which said it was encouraged by his willingness to take on corporations.

Among Kennedy's suggestions is that he would gut the 18,000-employee Food and Drug Administration (FDA) – which ensures the safety of food, drugs and medical devices – and replace hundreds of employees at the National Institutes of Health.

"FDA's war on public health is about to end," he wrote on X in late October, adding that includes its "aggressive suppression" of psychedelics, peptides, stem cells, raw milk, sunshine and other items.

"If you work for the FDA and are part of this corrupt system, I have two messages for you: 1. Preserve your records, and 2. Pack your bags," he wrote.

Shares of vaccine makers, including Pfizer and Moderna, fell after news of Kennedy's appointment and were down in after-hours trading by as much as two percent.

Kennedy has been criticised for making false medical claims, including that vaccines are linked to autism. He opposed state and federal restrictions imposed during the Covid-19 pandemic and was accused of spreading misinformation about the virus.

He disputes the anti-vaccine tag, saying he instead wants more rigorous testing of vaccines. However, he chaired the Children's Health Defense, a non-profit organisation that focuses on anti-vaccine messaging. (Reuters)