A top Food and Drug Administration (FDA) safety official submitted his resignation this week, citing progress on tackling the U.S. infant shortage formula while also expressing frustrations with the structure of the agency.

Frank Yiannas, the FDA’s Deputy Commissioner for Food Policy and Response, joined the agency in 2018 after having previously worked for several decades in food safety for Walmart and Walt Disney World Co. His last day with the agency is set for Feb. 24.

In his resignation letter to FDA Commissioner Robert Califf, Yiannas noted he had considered leaving in February 2022 due to his concerns over the “decentralized structure of the foods program” that he and Califf found themselves working with.

Yiannas, however, said he decided to postpone his exit in light of the infant formula incidents — the presence of bacteria in powdered formula that led to at least two deaths — and subsequent shortages that were reported to the FDA around that same time.

During the infant formula shortage last year, Yiannas publicly expressed his dissatisfaction with how information about the ongoing crisis was shared. In an interview with The Washington Post published in May, he said he had not been made aware of a whistleblower complaint about unsanitary conditions at a baby formula plant until four months after it was sent to the FDA.

“How does this happen?” Yiannas said at the time. “There were early signals, and in any safety profession you want to take those seriously to stop the domino effect. That didn’t happen.”

The Justice Department announced last week it has launched a criminal investigation into the Abbott plant in Michigan due to evidence of the unsanitary conditions.

Yiannas wrote in his letter to Califf that improvements that have been made since the crises first started have encouraged him to leave the agency.

“With the Abbott facility now reopened, infant formula availability more prevalent, and – very importantly – the necessary monitoring, data systems, and insights now in place through the 21 Forward platform to help address the current and any future infant formula supply chain challenges, I believe the time is right for me to leave and vacate this position,” Yiannas wrote.

He added that public organizations like the FDA that undergo crises like the infant formula shortage should conduct thorough reviews to understand how such emergencies occurred.

The official also wrote he believed the FDA would be more effective if it adapted a more “integrated structure” as well as a “fully empowered and experienced Deputy Commissioner for Foods” who had direct oversight over the relevant offices.

“The agency thanks Mr. Yiannas for his service and dedication to the FDA’s public health mission. Mr. Yiannas has served as a valued member of the agency’s leadership team, spearheading important initiatives including the New Era of Smarter Food Safety to help create a safer and more digital, traceable food system for our country,” an FDA spokesperson said in a statement to The Hill.