Dr Webby, director of the World Health Organisation's Collaborating Centre for Studies on the Ecology of Influenza and a researcher at the United States health institute the St Jude Centre, said the risks of flu viruses with animal origins had not diminished "one iota".
"In the past 12 months alone we've seen multiple confirmed human infections from three new animal influenza viruses; two from birds and one from pigs," he said.
"However recent research suggests that these viruses have not yet developed the ability to transmit between humans, but it's still possible."
Dr Webby said an increase of new viruses was of concern.
"Viruses are very, very clever, infinitely adaptable and unpredictable. We saw this in 2009 when all the focus was on avian viruses in Asia, but then the swine flu virus suddenly transmitted to humans in Mexico."
Along with his lecture at Otago University's Wellington campus today, Dr Webby is visiting New Zealand to meet with researchers from the Shivers - the Southern Hemisphere Influenza Vaccine Effectiveness Research and Surveillance project.
The project, commissioned by the US Centres for Disease Control and Prevention, is investigating internationally important questions about influenza, including its impact on hospital admissions and the effectiveness of current vaccines.
The research is led and coordinated by the Institute of Environmental Science and Research (ESR), in close collaboration with the Universities of Otago and Auckland, the Auckland and Counties Manukau District Health Boards, and Dr Webby's St Jude Centre.