Dr. Peter Marks, the Food and Drug Administration’s top vaccine official who played a crucial role in the development of COVID-19 vaccines during the pandemic, has resigned, with one source telling ABC News that he was pushed out of his position by Health and Human Services Secretary Robert F. Kennedy Jr.

Marks, who has served as the FDA’s vaccine chief since 2016, resigned in a letter sent to acting FDA Commissioner Sara Brenner. In it, he alleged Kennedy is not interested in “truth and transparency” but rather in “subservient confirmation of his misinformation and lies.”

Marks called the measles outbreak a reminder of “what happens when confidence in well-established science underlying public health and well-being is undermined.”

The measles vaccine “very simply does not cause autism,” Marks wrote.

“My hope is that during the coming years, the unprecedented assault on scientific truth that has adversely impacted public health in our nation comes to an end so that the citizens of our country can fully benefit from the breadth of advances in medical science,” Marks wrote.

A source familiar with the situation told ABC News that Marks was given the choice by a department official either to resign or be fired.

Asked for comment, an HHS official said, “If Peter Marks does not want to get behind restoring science to its golden standard and promoting radical transparency, then he has no place at FDA under the strong leadership of Secretary Kennedy.”

Marks has been the FDA’s vaccine chief since 2016. His resignation will end nearly a decade of monitoring vaccine development, evaluating their safety and recommending how the public should use them — and perhaps doing the role during one of the most critical eras in public health.

His role became incredibly high profile during the pandemic, when Marks oversaw the approval of the first coronavirus vaccines — and oversaw the intensely watched process through the many developments.