The President’s Council of Advisors on Science and Technology recently submitted its report to the president in which they stated that this influenza season might kill 30-90,000 people in the US. This forecast of the upcoming season caught the media’s attention and appears to have stoked the public interest in influenza. We have had many requests for more information about influenza here at SBM, and so in this post I am going to discuss the basics of influenza and try to put the current pandemic and upcoming season in perspective.
I find it is best to start at the beginning.
What Is Influenza?
Within the public sphere, “The flu” has become shorthand for “I feel like crap.” I suspect that this is part of the reason why some people think the influenza vaccine doesn’t work. Medically speaking, however, influenza is a very specific family of viruses that cause a reasonably narrow set of problems for humans.
The influenza season in the Northern hemisphere usually runs from October through May, with a peak mid-February. Every season in the US between 5-20% of the US population is infected by influenza, and while the majority of people recover well from an influenza infection, not everyone will. Annually 200,000 people are hospitalized, and on average 36,000 will die either from influenza or its complications.
The classic influenza infection incubates for 1-4 days after exposure. Its onset is rapid, with most people experiencing high fever, headache, muscle aches, dry cough, sore throat, and nasal congestion. Gastro-intestinal symptoms like nausea, vomiting, and diarrhea are less common. Symptoms last from several days to almost two weeks, and a person is contagious from one day before symptoms begin to more than a week after symptom onset.
There are many strains of influenza. The current seasonal influenza is made up of three different influenza subtypes: A(H3N2), A(H1N1), and B. Don’t confuse the seasonal A(H1N1) strain with the current pandemic 2009 A(H1N1); they are distinct. I will refer to them as A(H1N1) for the seasonal strain, and 2009 (H1N1) for the pandemic “swine flu” strain. Influenza B is less common, less virulent, has a slower mutation rate, and is thus a lesser risk; the rest of this discussion is focused on Influenza A. (more…)