[Having engaged in several spirited conversations on various other online forums, I thought the below further explanation might shed more light on the basis of the concern stated in the prior post. -JW]
The issue with the current circulation of A/H3N2 variant is:
The influenza A/H3N2 variant is a triple-reassortant virus. Federally funded and peer reviewed studies have suggested this agent is capable of triggering a "pandemic", however the probable outcome is the emergence of another "wave" of vigorous, socially disruptive transmission. This is predicated on lack of an available vaccine. That said, HHS/CDC considered the virus concerning enough to advance seed stock to the vaccine manufacturers for mass production.
There is no apparent herd immunity in the pediatric population. The parameters at the ag fairs indicate a high degree of efficiency in swine-human transmission. Human to human transmission this summer has yet to be identified, however last summer this was suspected as several of the cases had no history of exposure to swine.
The driving concern from a virulence perspective is NOT case fatality rate but the potential for abrupt and explosive transmission at a national / global level, producing a situation of infrastructure inundation. The law of numbers predicts greater numbers of patients hospitalized and recognition of the first fatality. The currently recognized case count precludes any firm conclusions about the clinical profile of this agent.
Comparisons to H5N1 highlight a typical human bias in focusing on the most severe clinical outcomes versus disease capable of generating acute, broad-scale disruption to medical infrastructure writ large. As stated in the original content, this situation therefore represents a serious risk. High morbidity disruptor agents are extremely difficult to surveil due to human bias in reporting mortality over morbidity- hence the reason why CDC in pushing diagnostic kits out to the state labs. Another indicator of the seriousness with which professionals in this domain are treating the issue.
The name of the game when it comes to medical infrastructure (and community) resilience is whether or not an infectious disease event is "routine". Unexpected explosive transmission of an agent like this is likely to generate infrastructure inundation according to this scheme: outpatient > inpatient > ICU level care > excession of capacity & capability.
The mitigation challenge is to determine how quickly an agent will evolve towards a profile of human-human transmission versus how fast we will recognize what is happening versus how fast vaccine can be put into production versus how quickly it can be distributed. As it stands, if A/H3N2 variant takes off, we have no vaccine at our disposal. HHS/CDC is certainly aware of this challenge, as indicated by their recent public statements.
The CURRENT profile of A/H3N2 variant is one of a mild infection but apparently very efficient at transmitting between swine and humans. Swine are considered "mixing vessels" for influenza viruses, which is the reason why this particular virus has genetic sequences from human strains of pandemic H1N1. Therefore, the forward evolutionary path of A/H3N2 variant is one of the following:
1. Nothing. The virus remains stable with the same clinical profile.
2. Further reassortment with circulating seasonal influenza strains to produce another variant able to transmit efficiently human-human... with an undefined clinical profile
3. Further molecular adaptation to humans, to produce another variant able to transmit efficiently human-human... with an undefined clinical profile.
4. A combination of #2 and #3 above.
5. Evolutionary competition forces A/H3N2 variant out of circulation.
The key question, not answered above, was how did pandemic H1N1 emerge in the first place? If one goes back to CDC advisories on swine influenza in the years preceding the 2009 pandemic, one notices the possible footprints of a virus that seemed at that time to be "not a big deal". Yet then we had an unexpected pandemic. On the other hand, H5N1 has failed for years to evolve to a point of efficient human-human transmission. Again, this shows the unpredictability of influenza virus molecular evolution... and how little we truly understand this pathogen.