Five new human cases of avian influenza in eastern China signal the potential for a new epidemic wave in the upcoming winter months, scientists said. The high-pathogenic H7N9 avian influenza earlier in 2013 first infected around 135 people and killed 45, but until five new cases emerged in October, health officials had thought human infections were on the decline.

The new cases indicate "a possible risk of a larger outbreak of H7N9 this winter," according to Chinese researchers writing in the online journal Eurosurveillance.

Ab Osterhaus, a leading virologist based at the Erasmus Medical Centre in the Netherlands who has been tracking the virus, told Reuters: "We're bracing for what's going to happen next."

The new cases also suggest the virus "has apparently continued to circulate in an animal reservoir during the summer," the researchers said.