More than one-third of H7N9 avian influenza tested in a new study was resistant to the antiviral drugs Tamiflu (oseltamivir) and Relenza (zanamivir), and lab tests failed to detect the resistance, making it tough to monitor, a new study says. "If H7N9 does acquire human-to-human transmissibility, what do we have to treat it with until we have a vaccine? Oseltamivir. We would be in big trouble," said researcher Robert Webster. "We'd better get some vaccine seed stocks up and ready. The antiviral option for controlling H7N9 isn't too good."