The emergence of drug-resistant influenza was documented in a study of Japanese patients. It is a clear early warning that flu viruses may be beginning to outwit what are now highly effective drugs, says Yoshihiro Kawaoka, a University of Wisconsin-Madison virologist and the senior author of the new JAMA study.

“There is urgent need to develop new kinds of antivirals,” says Kawaoka, an internationally recognized authority on influenza. “This is the first report that drug-resistant influenza B virus may be transmitting in the community.”