Two officials working on COVID-19 vaccine regulation have quit the Food and Drug Administration, reportedly over frustrations with the Biden administration. Dr. Marion Gruber, head of the FDA’s Office of Vaccines Research & Review, will finish up in October. Gruber is a 32-year veteran of the FDA, and has helped fight outbreaks of the flu, Ebola, MERS, Zika, and SARS. Her deputy, Dr. Phil Krause, will leave the following month.

The FDA didn’t give a reason for their departures but Endpoints News, a biotech industry outlet, reported that Gruber and Krause were frustrated that the CDC was making decisions that should be made by the FDA. The final straw was reportedly the Biden administration’s announcement that COVID booster shots would be made available—before the FDA had finished evaluating data on the need for a third jab. The officials’ departure threatens to further destabilize an agency plagued by a lack of a fixed leader. Janet Woodcock, current acting commissioner, will likely not be considered for the permanent position.