The WHO global influenza surveillance and response system (GISRS)—A future perspective

Hay, Alan J; McCauley, John W

Much has been learned about the mechanism of HA binding to the different receptors on avian/animal and human cells for various avian subtype viruses, H5N1, H5N6, H7N9, H9N2 and H10N8, isolated from infected humans, and has indicated that affinity for both types of receptors may represent an intermediate in acquisition of human-to-human transmissibility. 50, 51 However, what changes would be required and what environment would be conducive to such changes in the HA and in other virus proteins to effect efficient human-to-human transmission is simply not known. 52, 53 Thus, tools for influenza pandemic risk assessment (such as IRAT from CDC 54 and TIPRA from WHO), which provide a comparative assessment of the perceived pandemic threats from zoonotic infections, in terms of severity (based on, eg the case-fatality ratio) and likelihood (based on frequency of human infection) and the characteristics of the virus being assessed, are limited in predictive capacity. While H7N9 viruses have a capacity to transmit by respiratory droplet between ferrets, 55 no increase in transmissibility between infected people has yet been detected, even during the largest outbreak in 2016-2017 and the emergence of a highly pathogenic avian influenza pathotype. 56 Nevertheless, while such a structured framework upon which to base an assessment of zoonotic viruses is imperfect, it provides a mechanism for prioritising the risks associated with specific viruses, and there can be no doubt that enhancement of collaboration between animal health and human health sectors under the One Health banner should also help to optimise the availability of useful information.