A new strain of avian influenza, H5N7, has been in the news recently, and every day brings with it reports of more cases and more deaths, principally in China. I am frequently asked: is this something to worry about?
It depends on the interpretation of the question. Any new strain of influenza is something for concern. Considering the mortality rates and the case fatality ratios of newly reassorted strains of influenza, we could see widespread and significant mortality and morbidity. At the same time, we must be circumspect before declaring a new strain as a potential public health emergency.
Much of the uncertainty comes from the fact that we do not know H5N7’s transmission dynamics: its R(0), or average number of people whom an infected individual infects. We do not know how virulent and pathogenic the strain is in even moderate numbers of people. In short, the basic characteristics of contagion and transmission are unknown. At this point, it is fairly certain that there is no human to human trnsmission. Were there human to human transmission, it might be time to be more concerned. Rather, H5N7 appears to be the product of genetic reassortment involving commercial and domestic fowl, and probably pigs as well. The same complex,, therefore, is probably involved here as it has been with many novel strains.
H5N7 does not appear to be completely new, although the media suggests, in many places, that it is. H5N7 was recognized in Italy in 2007.
So what are we to make out of what we see with H5N7? At this point, it bears watching through various surveillance tools available, including Flu View, WHO, CDC, ProMED, and others. I always have a great deal of respect for the destructive potential of influenza. However, during the same week that CDC has declared our period of seasonal flu transmission to be over, let’s just keep an eye on H5N7.
WHO and CDC are now ramping up a response. There is even a vaccine candidate according to WHO. It does look like it is developing into a very fatal, novel strain. Humans, pigs and birds affected now.
Thanks, Jim. I think that the candidate vaccines are for H7N9. See
Of course H7N9 is receiving a great deal of attention and publicity right now.
Yes you are right, with three strains with the potential to harm humans, it is hard to keep them sorted this year. Has there ever been so many with this much potential danger developing at once?