A: There are two principal factors that have reduced the level of transmission among birds and other animals in Southeast Asia and China at the present time. One is the mass vaccination campaigns in domestic fowl that have been undertaken in some areas. The other is that a large number of surviving wild birds now have protective antibodies to the virus and thus do not transmit it. Both these factors serve to interrupt transmission. That said, however, because the life spans of both wild and domestic birds are relatively short, younger wild birds will not have natural immunity and would be susceptible to the virus and could spread it once infected. -- answered by Imperato
Q: Since the regular flu season is coming to an end this spring, are the chances of the bird flu mutating into a pandemic less likely this year?" -- Lisa, Worcester, Mass.
A: Influenza viruses of all types regularly undergo varying degrees of either mutation or "re-assortment" [changes in their genes]. These changes take place throughout the year and are independent of the yearly flu season. Newly mutated or re-assorted viruses generally cause outbreaks during the regular flu season in the Northern Hemisphere between the months of October and March.
It is not likely that the bird flu virus, H5N1, will cause a pandemic this flu season. However, the virus is being closely monitored in order to determine if it mutates or re-assorts and in doing so if it acquires the ability to be easily transmitted from human to human. The possibility still exists that this bird flu virus could cause scattered human cases, local epidemics or even a pandemic in the future. -- answered by Imperato