"We need to be very vigilant. This is something that we talked about a lot this morning," French Health Minister Xavier Bertrand said on the sidelines of a meeting of the Global Health Security Initiative (GHSI) in Paris.
The GHSI comprises the G7 group of industrialised nations along with Mexico, the European Union's Commission and the World Health Organisation (WHO).
A research team led by Ron Fouchier at Rotterdam's Erasmus Medical Centre said in September it had created a mutant version of the H5N1 bird flu virus that could for the first time be spread among mammals.
The H5N1 strain of bird flu is fatal in 60 percent of human cases but only 350 people have so far died from the disease largely because it cannot, yet, be transmitted between humans.
The announcement led to fears the mutant virus could find its way into nature or that the publication of the research on how the virus was mutated could be used by terrorists.
EU Health Commissioner John Dalli told journalists he had received assurances from Dutch authorities that the virus was secure.
"The Dutch authorities confirmed that the virus itself is stored in a very secured way and that the necessary permits were given and that the researchers are bound by a code of conduct," Dalli said.
"One of the issues ... is to ensure that any information coming from this research is well controlled and without sensitive details about mutation being given," he said.
Fouchier said in a statement his team had discovered that transmission of the virus was possible between humans "and can be carried out more easily than we thought."
"In a laboratory, it was possible to change the H5N1 into a virus ... that can easily be spread through the air. This process (mutation) could also happen naturally," Fouchier said.