Mammalian-Transmissible H5N1 Influenza: Facts and Perspective

Abstract

Two recently submitted (but as yet unpublished) studies describe success in creating mutant isolates of H5N1 influenza A virus that can be transmitted via the respiratory route between ferrets; concern has been raised regarding human-to-human transmissibility of these or similar laboratory-generated influenza viruses. Furthermore, the potential release of methods used in these studies has engendered a great deal of controversy around publishing potential dual-use data and also has served as a catalyst for debates around the true case-fatality rate of H5N1 influenza and the capability of influenza vaccines and antivirals to impact any future unintentional or intentional release of H5N1 virus. In this report, we review available seroepidemiology data for H5N1 infection and discuss how case-finding strategies may influence the overall case-fatality rate reported by the WHO. We also provide information supporting the position that if an H5N1 influenza pandemic occurred, available medical countermeasures would have limited impact on the associated morbidity and mortality.

H5N1 influenza virus seroepidemiological studies: The facts revisited

“…Although available evidence supports the fact that asymptomatic infections with H5N1 can occur in persons exposed to the virus, the evidence does not suggest that asymptomatic infections are common or that the case-fatality rate for H5N1 has been significantly overestimated (5). There is no evidence to support the statement by Palese and Wang that "the case-fatality rate that is offered by the WHO-and that is driving this controversy-is likely orders of magnitude too high" (1).…”

Is H5N1 Really Highly Lethal?

“…30,31 Both concluded that, if the 4 Hong Kong Clade 0 studies were excluded and if the 13 studies that conform to official WHO criteria are analyzed, the seropositivity rate is approximately 0.5%. A total of 26 out of 5,487 people were seropositive for H5N1 in those studies.…”

Does exposure to poultry and wild fowl confer immunity to H5N1?

“…41-45 Indeed, some have argued that the 1997 HK outbreak is irrelevant due to the genetic dissimilarity of the 1997 strain from later H5N1 strains. It is possible, as was suggested in a recent review, 46 that strains of different genotypes may differ in infectivity and transmissibility characteristics.…”