# 4105
With the fall wave of the pandemic H1N1 virus appearing to be on the wane in North America (it is still going strong in Europe & Asia), and with at least 5 more months of our traditional flu season to get through, there are a number of open questions as to what happens next.
- Will we see additional pandemic waves this winter or spring?
- Will the rest of the flu season sputter out like a damp squib?
- Or will the recently supplanted seasonal flu viruses stage a comeback?
To get an idea of where things may be heading, it is useful to look at the influenza history of the past 90 years.
Up until 1977, we only saw one influenza `A’ strain in circulation at a time. And that was – up until that time – thought to be the normal scheme of things.
As you can see in the chart above, in 1918 a pandemic of H1N1 supplanted whatever influenza `A’ (possibly H2N2) was circulating before that time, and for the next 40 years, was the solitary `A’ strain in the wild.
In 1957, a new reassorted virus (H2N2) emerged with the Asian Flu, and even though it was a relatively mild pandemic, it very quickly replaced the H1N1 virus.
Again, just eleven years later, a new virus (H3N2) arrived in the form of the Hong Kong Flu, and the (now seasonal) H2N2 was no more.
Each time a new virus appeared, it drove out the competition. Exactly why? Well . . . we don’t really know why.
But that was the pattern.
Until 1977. That year an old foe, in the form of the H1N1 virus, re-appeared after a 20 year absence.
How and why it returned is a mystery, although many believe it was the result of an accidental release from a Russian research laboratory.
It was dubbed the `Russian Flu’, and quickly spread among the under-20-somethings who had no immunity.
But this time things were different. It didn’t replace or drive out the existing (H3N2) virus.
The reason most commonly given is that older people were less affected by the returning H1N1 virus – since those born before 1957 had previous exposure – and so they remained a reservoir of the H3N2 virus.
The two strains (H3N2 and H1N1) co-circulated, and for the past 33 years having two main `A’ strains in circulation (along with some `B’ viruses) has been the norm.
Once again, we are faced with the introduction of a new virus, the novel H1N1, and once again it has a predilection for those born after about 1957.
A bit surprisingly, the existing seasonal `A’ strains (H3N2/H1N1) have all but disappeared this fall despite there being an ample reservoir of 60+ year olds out there that are less affected by H1N1 and vulnerable to the older strains.
With a declining pandemic wave, and months left to the regular flu season, the question becomes:
Will seasonal flu strains come back?
Will the elderly, who have been largely spared with this pandemic virus, now have to deal with a second, separate flu season later this year?
And right now, no one seems to know the answer to that question.
Complicating matters is the emergence of a new H3N2 variant which is not well covered by this year’s seasonal flu vaccine; the Perth/16/2009 strain.
Since this variant didn’t appear until spring (it was little noticed by the media amid the swine flu outbreak) it was not included in this year’s flu shot.
While the existing seasonal flu shot may offer some protection against this strain, how much that might be is unknown, and it is not expected to be optimal.
So . . . if we should see a resurgence of seasonal flu later this year, and if the Perth H3 virus is a major component (a couple of big `ifs’), we could well see a second very nasty flu season for the over-60 crowd.
Maybe.
Or maybe novel H1N1 has put a stake through the heart of the seasonal viruses. We really don’t know.
Today is December 1st, and in a normal flu season in the Northern Hemisphere, we’d be just starting to see our first major flu surge of the season.
Instead, we find ourselves watching the fall wave of the pandemic begin to recede, and with another 5 months of flu season to go, are left waiting for the other flu to drop.
The possibilities are – if not exactly endless, at least myriad.
The consensus is that the novel H1N1 is probably here to stay. At least until another, better adapted virus, comes along and supplants it.
In a year or two, it will probably lose pandemic status, and become the seasonal flu.
Of course, if H1N1 picks up significant mutations, or reassorts with other viruses, all bets are off. That’s the fascinating thing about influenza viruses. They are unpredictable.
There are many scientists who fully expect a 3rd wave, perhaps after the Christmas holidays, from the pandemic virus. (see Branswell: Some Scientists Expect A 3rd Wave). A lot will depend on the uptake of the vaccine, and how many people have gained immunity over the summer and fall.
Stay tuned.
There is no reason right now to believe that the `B’ viruses will go away, even if novel H1N1 becomes king of the viral mountain. So even if the pandemic virus sputters, we could see a lot of `B’ virus this spring.
Again, Maybe.
The big question is whether H3N2 and seasonal H1N1 have gone into the dustbin of history?
Or are they safely ensconced in some host reservoir somewhere, waiting for the right opportunity to return?
While I don’t know how all of this will play out, I have little doubt that there are more than a few surprises in store for us over the months and years to come.
Just as soon as we start feeling smug, and begin to believe we’ve figured out how influenza is supposed to work, it throws a wrench into things.
Just to keep us humble.
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