Since 1997, when the first human infections with the H5N1 avian influenza virus were documented, the virus has undergone a number of changes.
These changes have affected patterns of virus transmission and spread among domestic and wild birds. They have not, however, had any discernible impact on the disease in humans, including its modes of transmission. Human infections remain a rare event. The virus does not spread easily from birds to humans or readily from person to person.
Influenza viruses are inherently unstable. As these viruses lack a genetic proof-reading mechanism, small errors that occur when the virus copies itself go undetected and uncorrected. Specific mutations and evolution in influenza viruses cannot be predicted, making it difficult if not impossible to know if or when a virus such as H5N1 might acquire the properties needed to spread easily and sustainably among humans. This difficulty is increased by the present lack of understanding concerning which specific mutations would lead to increased transmissibility of the virus among humans.
[...] Assessments of the outbreak in Turkey, conducted by WHO investigative teams, have produced no convincing evidence that mutations have altered the epidemiology of the disease in humans, which was similar to the pattern consistently seen in affected parts of Asia. There is no evidence, at present, from any outbreak site that the virus has increased its ability to spread easily from one person to another.
Read the full press release on the WHO site. Effect Measure wonders what the un-"convincing" evidence from Turkey may be.
In another statement by a WHO official quoted by Nicholas Zamiska for the WSJ (subscription required) we get an update on the situation in Indonesia:
There is no evidence that the bird-flu virus in Indonesia has mutated to a form that is readily transmissible among humans, the World Health Organization said, despite increasingly alarmed reports from Indonesian health officials.
Clusters of the disease among Indonesians may well indicate human exposure to the same sick birds, the WHO said, rather than the transmission of the disease from human to human, an event scientists fear could spark a pandemic.
"Should we be more worried? Not at this stage," Sari P. Setiogi, a spokeswoman for the WHO in Jakarta, said in an interview, adding that as health-care workers in the field become more aware of the disease, the number of reported cases may rise.
