Transmission and infection of H5N1

H5N1

Influenza A virus subtype H5N1 Genetic structure Infection Human mortality Global spread in 2004 in 2005 in 2006 in 2007 2020–2024 Social impact Pandemic Vaccine

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Transmission and infection of H5N1 from infected avian sources to humans has been a concern since the first documented case of human infection in 1997,^[1] due to the global spread of H5N1 that constitutes a pandemic threat.

Infected birds pass on H5N1 through their saliva, nasal secretions, and feces. Other birds may pick up the virus through direct contact with these excretions or when they have contact with surfaces contaminated with this material. Because migratory birds are among the carriers of the H5N1 virus it may spread to all parts of the world. Past outbreaks of avian flu have often originated in crowded conditions in southeast and east Asia, where humans, pigs, and poultry live in close quarters. In these conditions a virus is more likely to mutate into a form that more easily infects humans. A few isolated cases of suspected human to human transmission exist,^[2] with the latest such case in June 2006 (among members of a family in Sumatra).^[3] No pandemic strain of H5N1 has yet been found.

Cumulative Human Cases of and Deaths from H5N1
As of April 11, 2007

Notes: Source WHO Confirmed Human Cases of H5N1 "[T]he incidence of human cases peaked, in each of the three years in which cases have occurred, during the period roughly corresponding to winter and spring in the northern hemisphere. If this pattern continues, an upsurge in cases could be anticipated starting in late 2006 or early 2007." Avian influenza – epidemiology of human H5N1 cases reported to WHO The regression curve for deaths is y = a + ek x, and is shown extended through the end of April, 2007.

H5N1 vaccines for chickens exist and are sometimes used, although there are many difficulties, and it's difficult to decide whether it helps more or hurts more. H5N1 pre-pandemic vaccines exist in quantities sufficient to inoculate a few million people^[4] and might be useful for priming to "boost the immune response to a different H5N1 vaccine tailor-made years later to thwart an emerging pandemic".^[5] H5N1 pandemic vaccines and technologies to rapidly create them are in the H5N1 clinical trials stage but can not be verified as useful until after there exists a pandemic strain.