In his first media interview since returning from an international scientific mission to China last week, Professor Angus Nicoll said the H7N9 flu outbreak in humans was one that should be taken extremely seriously and watched closely.
"We are at the start of a very long haul with H7N9," Nicoll told Reuters in a telephone interview from the Stockholm-based European Centre for Disease Prevention and Control (ECDC), where he is head of the influenza and respiratory viruses programme.
Nicoll noted that genetic analysis studies of H7N9 samples taken from patients in China showed the virus had already acquired two genetic mutations that made it more likely to be able to become transmissible between people.
Flu experts speaking at a briefing in London on Wednesday said those mutations, together with evidence that H7N9 is still mutating rapidly and probably spreading almost invisibly among birds because it does not make them obviously sick, meant this new flu was a "serious threat" to world health.
"You can never predict anything about flu, but it is concerning to see those mutations there, Nicoll said. "That's why it's important Europe should take this very seriously."