Victoria's Department of Health and Human Services is too big and should be broken up in the wake of failures in the state's hotel quarantine system, director of health at the Grattan Institute Stephen Duckett warns.

Former DHHS secretary Kym Peake was on Thursday the latest to step down in the wake of an inquiry into the hotel quarantine program, which was responsible for the state's second wave of the virus, following departures by former health minister Jenny Mikakos and premier's department head Chris Eccles.