What to know
This graph shows reported human infections with highly pathogenic avian influenza (HPAI) A(H5N1) virus (H5N1 bird flu) since the first human case in 1997.
Background
This graph shows reported human cases of infection with highly pathogenic avian influenza (HPAI) A(H5N1) virus, beginning with the first human case identified in 1997, and including cases reported to the World Health Organization (WHO) to date since 2003.*
HPAI A(H5N1) viruses that have infected people were first identified in poultry in southern China in 1996. Those viruses caused large poultry outbreaks in Hong Kong in 1997, which were associated with the first known human infections; overall 18 people were confirmed with HPAI A(H5N1) virus infection, resulting in mild to severe illness, including 6 deaths. The 1997 HPAI A(H5N1) outbreak in Hong Kong was controlled, but HPAI A(H5N1) viruses were not eradicated in birds. Beginning in 2003, the viruses spread widely in birds throughout Asia, and later in Africa, Europe, and the Middle East, causing poultry outbreaks and associated sporadic human infections.
In people with HPAI A(H5N1) virus infection, illness severity has ranged from mild to fatal, with a small number of people identified who did not experience any symptoms. Since 1997, 25 countries, including the United States, have reported a cumulative total of more than 1,000 sporadic human infections with HPAI A(H5N1) viruses, and approximately 48 percent have died.
Differences between older and recent HPAI A(H5N1) viruses
HPAI A(H5N1) viruses are currently circulating among wild birds and poultry in different regions of the world and continue to evolve. These recent viruses are genetically different from earlier HPAI A(H5N1) viruses. The recent HPAI A(H5) viruses became the predominant subtype of HPAI A(H5) viruses in the fall of 2021. These viruses have caused wild bird infections and poultry outbreaks in many countries, including the United States, with spillover to mammals in some regions. Sporadic human infections with current HPAI A(H5N1) viruses have been reported in some countries in recent years in different regions (Asia, North and South America, Europe) with a wide range of disease severity.
*Some reported cases tested positive for influenza A(H5) viral RNA but the neuraminidase subtype was not identified; these cases were presumed to be due to HPAI A(H5N1) virus infection. The graph does not include cases identified with HPAI A(H5) virus infection due to other neuraminidase subtypes, such as HPAI A(H5N2), A(H5N5), A(H5N6) viruses.
These data are updated biweekly on Fridays. For more data on A(H5) cases in the United States, visit: H5 Bird Flu: Current Situation | Bird Flu | CDC.