Anyone who as been following seasonal flu the past few years is aware that the H3N2 strain has become the problem child of the flu world, as it continues to evolve rapidly, and has diversified into numerous co-circulating subclades.
As a result, vaccine candidate virus selection for the seasonal flu vaccine has been greatly complicated, and VE (Vaccine Effectiveness) against H3N2 has been `suboptimal' at best.While all influenza viruses evolve incrementally via antigenic drift (or abruptly, via reassortment), the H3N2 subtype has been an over-achiever for the past 4 or 5 years. Today we learn, via a report in the Journal of Infectious Diseases, that H3N2 isn't alone.
The authors report that H7N9 - which is ranked by the CDC as having the highest pandemic potential of the currently circulating novel flu viruses - is mutating at a rate comparable to H3N2.
While H7N9 activity has been dramatically dampened down over the past 12 months following China's roll-out of an experimental poultry vaccine, today's study raises new questions over how long that vaccine formula will remain effective.First the abstract, and a couple of small snippets from the body of the study, then I'll return with a bit more.
Not all mutations in the flu virus are bad, in fact, most either prove benign or actually detrimental to the virus's overall biological fitness.
Our understanding of exactly what amino acid substitutions (or, more likely what combination of substitutions) really matter is still fairly limited, a topic that is addressed in a review of the above study, appearing in the same issue of the JID.Both articles are available for download as `accepted manuscripts' in PDF format.
(Continue . . . )
As we've discussed previously (see Sci. Reports: Efficacy Of AI Vaccines Against The H5N8 Virus in Egypt), well matched poultry vaccines can be very effective in preventing morbidity and mortality, and reducing viral shedding, in infected poultry.
But as avian viruses evolve, existing poultry vaccines become increasingly less effective (see Egypt: A Paltry Poultry Vaccine). and history has shown many countries continue to use outdated vaccines.Poor vaccine matches can then allow AI viruses to spread silently among flocks, to continue to reassort and evolve, and potentially lead to the emergence new subtypes of avian flu.
All of which means that the welcomed lull in H7N9 activity in China today may not last forever, and that China's MOA must be prepared to continually refine their poultry vaccine to deal with a rapidly changing virus-scape, if it is to remain effective.
And of course, vaccine candidates for humans will need to be updated frequently as well, which means that stockpiling large quantities of any H7N9 pandemic vaccine in advance is likely futile.