MINNEAPOLIS (AP) — The U.S. Department of Agriculture says a bird flu vaccine doesn’t work well enough to approve it for emergency use against the current outbreak that’s shaken the Midwest poultry industry. The USDA’s Animal and Plant Health Inspection Service said in a statement Wednesday that the current vaccine is not well matched against the H5N2 virus and don’t provide enough protection.

It says the vaccine offers just 60 percent effectiveness in chickens, leaving four in 10 birds unprotected, while the vaccine’s effectiveness in turkeys is still being studied. The USDA says it will continue to support efforts to develop a more effective vaccine. The agency says bird flu outbreaks have cost chicken and turkey producers more than 45 million birds so far, mostly in Iowa and Minnesota.