Scientists in China are saying there is evidence to show that a new strain of bird flu, the H7N9, is transmissible between humans.
The first case of H7N9 human infection was reported by Chinese authorities in March this year and by the end of May there were 132 cases and 37 deaths in China, along with one case in Taiwan.
Dr Alan Hampson, the chairman of the Influenza Specialist Group in Australia, has told Radio Australia's program the make-up of this new strain of bird flu makes it more transmissible between humans than the H5NI virus.
"When some of the work was done with the H5N1 looking at the characteristics that might make it more transmissible ... from one animal to another, some of those changes have been seen to actually exist already in the H7N9 virus," Dr Hampson said.
"There is a feeling that this virus may, with few other changes, become a virus that transmits steadily from person to person."
The recent death of an ailing father and the daughter who cared for him is being seen as evidence of possible human transmission of the H7N9 virus, although the 43 people who were in contact with the two parties have tested negative to the virus.
Professor Anne Kelso, the director of the WHO Collaborating Centre for Reference and Research on Influenza, says the virus found in both parties are genetically similar.
"Of course there could be a genetic element in determining susceptibility to severe disease, but the close contact is really likely to be the most important point at this stage," Professor Kelso said.
After the initial burst of reported infections, there appears to be a lull with only one case reported last month.
Professor Kelso says while this may indicate a containment of the virus there is still a need for vigilance.
"That might be partly because of the shutting down of the live bird market but also because of the change of seasons," she said.
"The really critical time to watch will be when the weather gets cold again in China, and when we might start to see more spread of influenza viruses in birds, that's the time when it looks as if there will be the biggest risk of a resurgence in H7N9."
Dr Hampson says unlike the earlier H5N1 virus, the source of the H7N9 virus is not known and the birds infected with the H7N9 virus are not showing symptoms of illness.
"We don't see the effect in poultry to any extent," he said.
"It's potentially travelling silently amongst the bird population so we don't know where it is and we don't know what the risks are."
Professor Kelso says this is making the job of sampling and testing domestic birds, pigeons and ducks an unwieldy task for Chinese authorities.
"The Chinese authorities have done a great deal of sampling of bird markets in different provinces and also farms," she said.
"They've done a lot of sampling, and found a few positive samples, but not as many as one might expect.
"It's still quite mysterious and I think there's still a lot of work to be done to understand exactly how this virus is spreading."
Professor Kelso says there is currently no vaccine for the H7N9 virus and existing prototype vaccines for the H7 influenza viruses are not likely to be of much use.
Governments and companies are now looking at making H7N9 vaccines to stockpile in the event of an outbreak.
Dr Hampson says what is also needed is continuous monitoring and exchange of information.
"Everybody has learned a lot from the H5N1 and from the SARS outbreak in terms of the need to be open, the need to transmit information, and the need for public health authorities within the affected countries and globally to actually respond to the things that are happening," he said.