WHO closely monitors the evolution of influenza viruses and is aware of recent reports of an H5N1 virus (described as H5N1 clade 2.3.2.1) circulating in poultry in parts of Asia. Based on available information, this evolution of the H5N1 virus poses no increased risk to public health. It is not considered unusual because influenza viruses are constantly evolving, especially in areas where they circulate regularly in poultry.

The WHO Global Influenza Surveillance and Response System, the group of experts that studies animal and human influenza viruses that may impact human health, recognized this new clade in February 2011.

WHO also routinely assesses the public health risk from all animal influenza viruses. Based on available information, the identification of this newly-reported H5N1 virus clade does not change the current public health implications of the H5N1 avian influenza viruses for humans. Human cases of H5N1 infection remain rare and sporadic events, occurring mostly in areas where H5N1 viruses circulate regularly in poultry. Human cases could occur wherever the viruses are present in poultry and when humans might be exposed to infected birds or contaminated environments.