The virus responsible for China’s most recent flu epidemic is just two mutations away from spreading easily between humans. But as H7N9 infects hundreds, some U.S. virologists who want to help are stuck on the sidelines, New Scientist reports. That’s because of a temporary U.S. ban on government funding for research that makes potentially pandemic viruses more dangerous or transmittable. The Department of Health and Human Services instated the policy in 2012 to counter bioterrorists, but researchers say those experiments may determine whether H7N9 can be spread in the air between mammals. Two other strains of bird flu—H5N8 and H5N6—are responsible for the killing and culling of millions of birds—including chickens—around the world.