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Public Health Threat of Highly Pathogenic Avian Influenza A (H5N1) Virus

The current highly pathogenic avian influenza (HPAI) A (H5N1) virus outbreak among poultry (epizootic) in some countries is not expected to diminish significantly in the short term. Thus, sporadic human infections with HPAI H5N1 virus resulting from direct or close contact with infected sick or dead poultry are expected to continue to occur and some of those cases will likely be fatal.

Influenza A viruses circulating among poultry have the potential to recombine with human influenza A viruses and become more transmissible among humans. If HPAI H5N1 viruses gain the ability for efficient and sustained transmission among humans, an influenza pandemic could result, with potentially high rates of illness and death worldwide. Therefore, the HPAI H5N1 epizootic continues to pose an important public health threat.

So far, the spread of HPAI H5N1 virus from person-to-person has been very rare, limited, and not sustained. To date, there is no evidence of genetic reassortment between human influenza A viruses and HPAI H5N1 viruses. There has also been no indication that these viruses are becoming more transmissible to humans or from human to human. Even though HPAI H5N1 viruses are spreading among poultry and wild birds and this increases the possibility of human exposures to infected birds or poultry, it has not increased the ability of HPAI H5N1 viruses to infect and transmit between people. (Infection and transmission among people remains a rare event.)

Because HPAI H5N1 viruses are always changing, CDC and other public health agencies look for genetic changes in HPAI H5N1 viruses that may impact how HPAI H5N1 viruses spread from person to person or their susceptibility to influenza antiviral drugs. To support international surveillance and pandemic preparedness efforts for highly pathogenic avian influenza A (H5N1) viruses, CDC has compiled an inventory of known HPAI H5N1 genetic changes. More information about the inventory is available at Questions and Answers: H5N1 Genetic Changes Inventory.

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