How many strains of polio or small pox were there?
Very few. Smallpox is a DNA virus and its replication enzyme has proof reading activity (RNA viruses don't, which is why there are so many strains compared to DNA viruses). Polio viruses have a single RNA molecule for their genomes, thus rely solely on point mutation for their genetic diversity. Influenza viruses are particularly crafty. They not only (1) get point mutations, but undergo (2) reassortment of their 8 RNA gene segments (like independent assortment of chromosomes in diploid organisms) and (3) can undergo recombination events with same gene segments of other influenza viruses. Each of these three types of mutations is evident in the H1N1 "swine" virus that is the topic of this thread.
As a consequence of this genetic "bag of tricks", there are literally hundreds, perhaps thousands, of influenza viruses in nature, circulating mostly in waterfowl. The bad thing is when you have exposure of domesticated fowl, swine and humans in close proximity. That is an environment for those genetic events to occur that can lead to the emergence of a new influenza strain.
That's not all that uncommon. For example, it happens occasionally when vaccine manufacturers make a poor prediction and create the wrong vaccine for an entire flu season.
Vaccine manufacturers do not select the three strains formulated in each year's vaccine. An independent committee does. They base their selection criteria (usually two type A viruses and one type B virus) upon the current predominant strains circulating globally. Unfortunately, because of influenza viruses' craftiness I discussed above, they're only right about 7 years out of 10. This year's vaccine (2008) has the following:
A/Brisbane/59/2007 (H1N1)-like virus
A/Brisbane/10/2007 (H3N2)-like virus
B/Florida/4/2006-like virus
Next year will be:
A/Brisbane/59/2007 (H1N1)-like virus
A/Brisbane/10/2007 (H3N2)-like virus
B/Brisbane/60/2008-like virus
Note the only change is the B virus. This is because more often than not a predominant strain circulates for about 3 years or so.
It is all a guess when they create a vaccine, they don't now what strain will hit until after it hits.
Most of the time they get a good match in a given year. And when they do miss it, it's usually because of an emergence of a new strain.
I shall weigh in with my opinion. I don't understand the big hubbub over this thing. I think it's really been blown way out of proportion. How many people die each year from the regular ol' 'flu? I thought so.
The last four global pandemics of serious influenza started in the spring as a mild form of influenza. The viruses returned in the fall with much more pathogenicity. This story won't be known until next winter (northern hemisphere). The 1918 pandemic strain infected almost a third of the US populace and killed about 2% of those infected, and the demographic was young, healthy adults. That is far more than seasonal influenza. I suspect there will be a special vaccine production run for this particular virus because time for a decision is running short. Have a read
here and stay tuned.
