H3N2 influenza virions –CDC PHIL
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Excluding the 2009 `swine flu pandemic virus’, there have been 31 `novel’ swine flu infections detected in the United States since 2005. Most of these cases appear to have come about from direct contact with pigs, and the CDC believes they have only involved limited human-to-human transmission.
Up until last year, the most common strain of S0IV (Swine-origin influenza virus) found in humans was a trH1N1, but in 2010 we began to see a shift towards trH3N2 viruses.
In November & December of 2010 we learned of three such infections (see CDC: Statement On Swine H3N2 Influenza and CDC: Another Novel H3N2 Isolate) arising from Pennsylvania, Wisconsin, and Minnesota.
This year, a new reassortant of trH3N2 has appeared on the scene that has picked up a the Matrix (M) gene segment from the 2009 H1N1 virus. Unlike most of the earlier novel swine flu infections, this strain has shown some signs of human-to-human transmission.
You’ll find some recent coverage of this emerging swine flu variant in the following blogs:
Branswell On The New trH3N2 Flu Virus
CIDRAP: New Details In The trH3N2 Story
ECDC Risk Assessment On trH3N2 Cases In North America
CDC Update On Iowa trH3N2 Cases
While only a small number of these trH3N2 infections have been detected, the assumption is that the virus may be circulating in a limited fashion under the radar. The concern is, that over time, it could get better at infecting humans and present a public health threat down the road.
As a precautionary measure, public health officials at the CDC have been working on getting a seed vaccine – a prototype – for this new virus into the hands of vaccine manufacturers.
Robert Roos of CIDRAP NEWS picks up the story, with details on how the CDC is using a similar trH3N2 swine virus – A/Minnesota/11/2010 – as a basis for a potential vaccine.
Vaccine virus for novel H3N2 based on 2010 swine flu strain
Robert Roos
News Editor
Dec 2, 2011 (CIDRAP News) – The Centers for Disease Control and Prevention (CDC) got a head start on preparing a vaccine against the novel swine-origin influenza strain recently found in four states by using a slightly different swine-origin strain that cropped up last year, CDC officials said today.
While the development of a seed vaccine for this novel strain is a prudent step, it should be noted that even if we assume that surveillance is only picking up a fraction of the cases that are out there, we are a long way from being in a pandemic situation.
As I wrote in Pseudo Pandemics And Viral Interlopers it is possible for new strains of influenza to appear and circulate among humans, without sparking a pandemic.
Short of causing a pandemic, this emerging trH3N2 virus could just simply sputter for a while and then die out. Or it might develop just enough `legs’ to co-circulate at low levels with our other seasonal flu strains.
We’ll have to wait to see if and just how well this virus adapts to human physiology, what level of immunity already exists in the population, and whether this strain is virulent enough to cause significant morbidity and mortality.
All factors that will determine the ultimate threat posed by this – or any other – emerging flu strain.
For now, the news is reassuring.
- Flu activity remains low across the nation.
- Only a handful of cases of trH3n2 have been identified.
- Most of those cases have involved mild to moderate illness.
- And work on a vaccine, should it be needed, is already underway.
Influenza, of course, is hugely unpredictable. What is true today may not hold true tomorrow.
This trH3N2 strain which has captured our attention over the past year could become a big story over the next few months, or it may turn out to be an interesting footnote in the history of influenza.
Stay tuned.
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