Wednesday, January 22, 2014

WHO Risk Assessment of human infection with avian influenza A(H7N9) virus

Some charts, and excerpts from the above document:

Virus characteristics
Laboratory analysis of H7N9 viruses isolated from humans, animals, and environmental samples
during the second wave indicates that the HA and NA genes remain similar to the viruses
isolated during the first wave, and that antigenically all the viruses are homologues and closely related to influenza A/Anhui/1/2013 (H7N9) virus, the recommended virus for H7N9 vaccine development.
Of recent viruses tested, no known amino acid substitutions were identified that are associated with
resistance to the neuraminidase inhibitors, including oseltamivir and zanamivir. Thus, the H7N9 virus is expected to be sensitive to neuraminidase inhibitors. All tested H7N9 viruses show
a substitution that confers resistance to the antiviral drug adamantine. 
Evidence for human-to-human transmission
Information to date does not support sustained human-to-human transmission.  WHO evaluates all clusters2 of human cases of non-seasonal influenza viruses to determine whether human-to-human transmission or common exposure to infected animals or contaminated environments may have occurred. Within the few clusters of human infection of influenza H7N9 reported thus far, where human-to-human transmission could have been a potential explanation, no further transmission was detected. Infection in health care workers is also of specific interest as it
might indicate health care associated human-to-human transmission. In the second wave, infection in one health care worker was identified. Investigation suggested possible exposure to poultry or contaminated environment as the likely source of infection, and no other human cases associated with this case have been identified.
All these suggest that the virus has not acquired the ability to transmit easily among humans.
However, given the detection of several less severe cases through ILI surveillance along with
the continued reporting of severe cases, continued vigilance is warranted.2   A “cluster” is defined as two or more persons with onset of symptoms within the same 14-day period and who are associated with a specific setting, such as a classroom, workplace, household, extended family, hospital, other residential institution, military barracks or recreational camp.

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