The Food and Drug Administration’s embattled vaccine chief, Dr. Vinay Prasad, is once again leaving the agency — the second time in less than a year that he’s departed after controversial decisions involving the review of vaccinations and specialty drugs for rare diseases.

FDA Commissioner Marty Makary announced the news to FDA staff in an email late Friday, saying Prasad would depart at the end of April. Makary said Prasad would return to his academic job at the University of California, San Francisco.

In July, Prasad was briefly forced from his job after running afoul of biotech executives, patient groups and conservative allies of President Donald Trump. He was reinstated less than two weeks later with the backing of Health Secretary Robert F. Kennedy Jr. and Makary.

Prasad’s latest ouster follows a string of high-profile controversies involving the FDA’s review of vaccines, gene therapies and biotech drugs in which companies have criticized the agency for reversing itself, in some cases calling for new trials of products previously greenlighted by regulators.

In the last month, Prasad has come under fire from pharmaceutical executives, investors, members of Congress and other critics for multiple decisions at the agency.

First, Prasad initially refused to allow the FDA to review a highly anticipated flu vaccine from drugmaker Moderna made with mRNA technology. The rejection of the application, highly unusual for the FDA, prompted Moderna to go public with Prasad’s decision and vow to formally challenge it.

A week after the rejection became public, the FDA reversed course and said it would accept the shot for review after all, pending an additional study from Moderna.

Then, in the past week, the FDA engaged in a highly unusual public fight with a small drug company developing an experimental treatment for Huntington’s Disease, a fatal condition that affects about 40,000 people in the U.S.

The company, UniQure, said Monday that the FDA was demanding a new trial of its gene therapy that would involve performing a sham surgery on some of the patients in the trial. The company’s gene therapy is injected directly into the brain during a surgical procedure.

Company executives said the request for a sham-controlled trial contradicted previous FDA guidance and raised ethical concerns for patients.

On Thursday, the FDA held a highly unusual press conference with reporters to criticize the company’s therapy and defend the agency’s request for an additional study.

A senior FDA official, who requested anonymity to speak with reporters, called the company’s original study “stone cold negative.”

“We have a failed product here,” he added.

The FDA typically communicates in carefully-vetted written statements when speaking about scientific disagreements, especially those involving experimental drugs that are still under the agency’s review.

Prasad’s time as the FDA’s top vaccine and biotech regulator has been marked by a series of similar disputes with the companies the agency regulates.

More than a half-dozen drugmakers studying therapies for rare or hard-to-treat diseases have received rejection letters or requests to run additional studies, adding years and potentially many millions of dollars to their development plans.

A longtime academic and critic of the FDA’s standards for drug reviews, Prasad’s approach to regulation since arriving at the FDA last May has confounded many FDA observers and critics.

On repeated occasions, Prasad joined Makary in announcing steps to make FDA drug reviews faster and easier for companies. But he also has imposed new warnings and study requirements for some biotech drugs and vaccines, particularly COVID shots that have long been a target for Kennedy, a longtime anti-vaccine activist before joining the Trump administration.