Influenza is not rare.
CDC current flu activity as well as activity the past few years. The WHO, Europe, and a few other countries have similar report web sites.
The flu is a serious respiratory infection not a stomach infection as many believe. There are ~200 known respiratory pathogens and the flu represents only a small percentage. But it kills many more people than most the others. If you have a sudden onset of a high fever, headache, muscle aches, and by the next day have a sore throat and cough during flu outbreaks it is more likely the flu than not. If you have a scratchy throat and runny nose that turns into a cough and has a mild fever it is unlikely to be the flu.
A considerably large portion of public health money is spent by all modern countries monitoring and evaluating flu risk annually. This includes monitoring human and animal influenza disease. The virus' genetic drift (and shift when recombinant strains emerge) is continually determined by sampling the virus from animals and humans as outbreaks circle the globe following the endless winter.
Vaccine composition is determined by the WHO twice a year based on what is actually circulating. Vaccine strain viral cultures maintained by the WHO are then distributed to vaccine manufacturers from which they produce vaccine. There is a southern hemisphere and a northern hemisphere version with production set for the fall in each hemisphere. It contains 3 strains because adding more gets you the law of diminishing return. You get very little additional coverage for circulating strains by adding more than 3. The vaccine will change 1,2 or 3 of the strains it contains from year to year.
The virus' lethality and complication rate are seriously underestimated by most people.
The vaccine is very safe compared to the risk from the disease.
It doesn't make you ill as many believe. There are placebo controlled studies showing that.
The vaccine is not the biggest money maker for drug companies which is one reason not enough is produced every year.
The current HPAI-H5N1 (bird flu) reminder that a deadly pandemic of influenza is cyclic and we have no means yet to stop it when it happens has renewed interest in potential profit therefore research has resumed in earnest among a few vaccine manufacturers.
A
recent study published which analyzed the viral changes of regular flu over a few years indicated it remains the same as far as your immune system recognizing it for long stretches then a new version will emerge and rapidly become the dominant strain. This happened recently
with H5N1 as well though the new version remains deadly and is not spreading among humans very efficiently just like the first version.
Original article (BTW, there are several H5N1 strains that are not very dangerous and are worldwide. The deadly version emerged from the mild strains in 1997.)
Your vaccine will last anywhere from several months to a few years depending on your immune system but since you don't get a 'series' it doesn't last as long as say a tetanus vaccine. However it's a moot point since the virus will drift enough to appear as a new organism to your immune system every year or two anyway.
Oh, BTW, as an infectious disease practitioner, I get a flu shot and give one to my son every year.
