A top veterinary official with the U.S. Department of Agriculture says more money, surveillance and farm security is needed to fight off a possible return of bird flu this fall.

David Swayne, director of a USDA poultry research laboratory, told the U.S. Senate Agriculture Committee on Tuesday that no new cases have been detected in three weeks.

But he says the government has increased of to detect any return of the virus, and is working with farms to improve biosecurity. He says work continues on a vaccine, and the USDA is hiring 460 temporary animal technicians as first responders in case the virus returns.

The outbreak has forced farmers to kill 48 million turkeys, chickens and other birds in 15 states, mostly in Iowa, Minnesota and Nebraska.