A Vietnamese study which has shown that there are signs of greater human to human transmission of bird flu, has prompted the UN health agency to call on countries around the world to continue with their preparations for a threatened flu pandemic.
The World Health Organization's (WHO) top influenza expert, Klaus Stohr says there have been enough warnings that another pandemic is coming, and health organisations should continue with preparations for a pandemic.
The emergence of the H5N1 bird flu virus among humans in Asia has raised fears that a new deadlier strain of flu might spread rapidly around the world on a similar scale to pandemics in the last century.
The study, which carried through to April 2005, of bird flu outbreaks in people in Vietnam, suggests an evolution of infections by the H5N1 virus.
The WHO examined the findings with experts from Cambodia, Thailand and Vietnam earlier this month, and has called for an immediate boost in monitoring for possible pandemic influenza in all countries affected by H5N1 in birds.
A report on the study says that the changes in the epidemiological patterns are consistent with the possibility that recently emerging H5N1 viruses may be more infectious for humans.
The UN health agency says that while that meant a greater number of people might be infected by poultry, there was also evidence that human-to-human infections, which have been found several times since the strain was first detected in Hong Kong in 1997, was strengthening, which raises the possibility that avian flu viruses are becoming more capable of human-to-human transmission.
However, according to the WHO, the study in Vietnam, because of the relatively small number of cases, cannot be considered conclusive.
Guenael Rodier, head of WHO's communicable diseases, says even though the report was in a 'grey zone ' and the implications are not clear cut, the viruses appear to be continuing to evolve and pose a continuing and potentially growing pandemic threat.
Thirty-six people have died from bird flu in Vietnam since 2003, as well as 16 in Thailand and Cambodia, and human to human transmission is believed to have occurred in two clusters of cases in Vietnam and one in Thailand.