David Geier has been hired as a senior data analyst at H.H.S. According to several people, he will examine any potential links between vaccines and autism that were debunked long ago.

A steadfast figure in the anti-vaccine movement who has helped shape Health Secretary Robert F. Kennedy Jr.’s thinking on a possible link to autism has joined his department to work on a study examining the long-debunked theory, according to people familiar with the matter.

The new analyst, David Geier, has published numerous articles in the medical literature attempting to tie mercury in vaccines to autism. In 2012, state authorities in Maryland found that he had been practicing medicine without a license alongside his father, Mark Geier, who was a doctor at the time.

Maryland authorities also suspended Mark Geier’s medical license following claims that he endangered children with autism and exploited their parents, according to state records.

Federal judges have rejected their research on autism and vaccines as too unreliable to stand up in court.

David Geier’s new government role has stunned public health experts, who had already expressed concerns about Mr. Kennedy’s decisions to cancel a long-held vaccine meeting and to cut grants focused on understanding vaccine hesitancy.

In addition, David Geier’s involvement in government research heightens their fears that vaccine confidence could be further eroded, especially after Mr. Kennedy’s recent embrace of questionable alternative treatments for measles during the sprawling outbreak in Texas.