The World Health Organisation (WHO) in its' efforts to determine whether the virus that causes bird flu is mutating, has been hindered by a lack of samples from infected birds and people in Asia.
The WHO has not received samples or genetic information from among others, Thailand, Vietnam and Cambodia, for the past eight months, strains of the avian virus had previously been found in poultry in these countries.
Of the dozens of people who have caught the deadly H5N1 virus from birds this year, only six samples have been obtained by WHO experts.
Klaus Stohr, the co-ordinator of WHO's flu program, says though several of the human samples contained a mutated form of the virus, it was not possible to judge the significance of this from such a small amount of data.
Stohr says, comparing the situation to everyday life, "It's as if you hear a noise in your car engine, but you keep driving, not knowing whether it's serious".
More than 89 people have been confirmed to have contracted avian influenza in the past 18 months, and more than 50 have died. Officials are concerned that recent clustering of human cases suggest there could be human-to-human transmission of the virus occurring rather than just people catching the disease from birds.
A variety of factors contribute to the lack of co-operation with WHO, including countries not having the resources to collect and securely transport samples or being unwilling to share information with outside authorities.
Vietnam apparently, only recently agreed to send a large number of poultry samples to a WHO laboratory in the U.S.
The report is published in the scientific journal Nature.