11:00 Dose of Fluology: What Exactly is Pandemic Flu?

What Exactly is Pandemic Flu?

Is it here?  Do I have it?  If I could have it, and I'm not dead, why should I be scared of it?  Wait, should I be scared of it?  Ahh!  Loud noises!

The answers, respectively, are: Not at the moment, probably not, there's a good reason/keep reading, vigilant but not panicked, and shhhhhh.

First thing's first, let's define "pandemic".  MedNet defines it as an epidemic (a sudden outbreak) that becomes very widespread and affects a whole region, a continent, or the world due to a susceptible population.  Good enough for me, though I would KO "region" from that list.  So a flu pandemic would be an epidemic that spans across the globe.  Because flu tends to be seasonal, and North America flu season is different from Australian flu season, to get a full-on flu pandemic concurrently happening all over the world requires some extenuating circumstances.  Those circumstances usually involve how virulent (ie, severe or deadly) a given flu strain is, and the background immunity of the world's population.  In this case, a pandemic-causing flu strain is usually quite virulent, and the world's population has little to no immunity.  

How does that happen, exactly?  Pandemic flu strains are nearly always newly emerging.  In other words, they didn't exist prior to the current pandemic.  Where do they come from, one might ask?  They arise from a process called antigenic shift, which I'll talk about this afternoon.  Sufficed to say, since they are new, and the human population has not yet "seen" them (immunologically speaking), they tend to rip through what is a completely susceptible population.  This is why they tend to have higher death tolls, and create a little more panic than "garden variety" flu.  Remember Patient #3 from the 10:00 dose: everyone is that sick, no one is immune, and it's a little scary.

Fortunately, flu surveillance is quite good, flu shots are reasonably straightforward to generate, oseltamivir is a good drug, and pandemic strain emergence is getting more and more straightforward to forecast.