# 3314
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Once upon a time we only had to deal with one Influenza `A’ strain at a time.
Oh, there were certainly minor exceptions.
Rogue flu strains may have flared briefly, failed to spread widely, and then disappeared. And probably even rarer still, occasional human infections from avian strains.
But despite these interlopers - during modern times at least - until 1977 we only had one Influenza `A’ strain to deal with each year.
What that strain was before 1918 is unknown (although some suspect H2N2). We weren’t able to isolate viruses until the 1930s.
But thanks to researchers,we now know that in 1918 a novel H1N1 (sound familiar?) virus appeared, touched off a horrific pandemic, and sent whatever influenza `A’ strain that had been in circulation packing.
H1N1, for reasons not entirely understood, completely replaced the existing `A’ strain.
And for nearly 40 years, the H1N1 virus remained king of the viral mountain.
Of course it mutated and evolved over the years . . .sometimes abruptly as in the pseudo-pandemic of 1947 (widespread illness, but very mild) or the killer Liverpool Flu of 1951 (see Sometimes . . . Out Of The Blue) . . . but most years it settled into a relatively mild and predictable pattern.
Until 1957, when a new usurper to the viral throne appeared, the H2N2 virus.
There are some scientists who believe that H2N2 had visited mankind in the late 1800’s, sparking the 1889-1890 pandemic, but the evidence for that is far from conclusive.
What we do know is that in 1957, this novel virus appeared in Asia (hence the name `Asian Flu’). It is believed to have come about through a reassortment of an avian flu strain with a human influenza.
In a matter of months it spread out of the far east, and circled the globe, causing the second pandemic of the 20th century.
In the United States, it is blamed for the deaths of nearly 70,000 Americans. Worldwide, the number is estimated anywhere between 1 and 4 million people.
And like the H1N1 virus before it, it completely wiped out its predecessor. In short order the H1N1 virus ceased to exist in the wild, although it remained `captive’ in laboratories around the world.
After nearly 40 years, the H2N2 virus had deposed the long reigning H1N1.
H2N2, which flared again in 1959-60, and again in 1962-63, would have a comparatively short time atop the viral mountain.
Just 11 years later, a new virus would appear – the H3N2 `Hong Kong Flu’, and like in 1918, and 1957, it would replace the existing flu strain.
Despite that fact that H3N2 was extremely mild, it wrestled the throne from its predecessor. H2N2 was no more.
It seemed to most scientists, that for reasons not entirely understood, only one influenza `A’ strain seemed capable of circulating at a time.
And then, in 1976, the H1N1 `swine flu’ appeared at Ft. Dix New Jersey, setting into motion the last big pandemic scare. Although only 1 soldier died, hundreds more were infected.
The United States, fearing a repeat of 1918, launched an ill-fated national pandemic vaccination program (see Deja Flu, All Over Again).
While the dreaded swine flu failed to appear the following fall, the very next year something remarkable happened.
After an absence of roughly 20 years, the H1N1 virus (remember it? It reigned from 1918 to 1957) suddenly reappeared.
Influenza A/USSR/90/77 (H1N1) caused what many people today term a pseudo-pandemic.
Since most adults older than their early 20’s had substantial immunity to this virus (it was around when they were children), its worst effects were felt by children.
It may not have been a true pandemic, but I can attest, it slammed the hospitals and emergency services where I was working pretty hard.
How this `lost’ strain reappeared after 20 years has long been a matter of conjecture, with many believing that it was accidentally released from a Russian research laboratory.
But unlike 1918, 1957, and 1968 . . . this newly emerging virus didn’t supplant the existing H3N2 virus.
In 1977 we began a new era, with H3N2 and H1N1 co-circulating around the globe. And this new paradigm has been in place now for more than 30 years.
In 2002, a third `A’ Strain was identified, the H1N2 – clearly an assortment between the H3N2 and the H1N1 virus. It appears no more virulent that its parents, and has produced no detectable surge in influenza cases.
And now, in 2009, we have another (novel) H1N1 strain entering an already crowded field.
It remains unclear whether it will co-circulate with the other 3 `A’ strains, or if it will eventually replace them.
Right now, in addition to two lineages of `B’ influenzas (Victoria and Yamagata) floating around the world, we now have 4 (count’em) Influenza `A’ strains.
H1N1 (classic), H3N2, H2N2, and now the novel H1N1 `swine’ flu. There are also small, but potentially serious outbreaks of avian flu viruses like the dreaded H5N1, the H7’s and H9’s.
You may be asking, why should we care?
Most of us have previous exposure, and some immunity, to a lot of these strains.
Why does it matter that there are now (at least) 4 different strains of human-adapted influenza `A’ rubbing elbows, along with a short list of avian viruses?
Aside from the complications this brings for creating seasonal flu vaccines, influenza viruses are both promiscuous and unpredictable. They have a long history of swapping genetic material and creating new, and quite often challenging, viral strains.
The more flu viruses in close proximity to one another, the better the chances of seeing reassortments.
Just like the more cars on the road, the better chance you have of seeing an accident. What we don’t know is what this complex brew of viruses will yield.
The `next big flu strain’ may turn out to be a wimp, such as we saw in 1968. New, or novel, doesn’t necessarily translate into virulent.
But there is always the danger that nature will gin up something nasty.
As you might imagine, these are exciting and interesting times for flu researchers.
We are watching, for the very first time, as a novel virus works its way into the existing flu mix and have a front row seat to watch how it interacts with other viruses.
We stand to learn a great deal over the next few years about how pandemics evolve. Even so, we remain mindful of the fact that not all pandemics arrive by the same route.
Hopefully what we learn over the coming months and years will help scientists devise new ways to protect humanity from the scourge of influenza.
A pity, since seasonal influenza kills an estimated 500,000 people each year, that it has taken the threat of a pandemic to get governments to allocate funds for research.
Better late, I suppose, than never.
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