Welcome to flu season! Let’s review.
Influenza is a virus that affects humans and several other species that often live in close proximity to humans such as domestic pigs and birds. The virus changes over time due to “antigenic drift”, often rendering immunity to previous strains irrelevant. If an animal is infected with two strains, they can recombine, leading to a new and very different virus, a process called “antigenic shift” which leads to pandemics.
Influenza is horrible. It usually strikes hard and fast, with muscle aches, cough, and fever (the usual case definition for influenza-like illness is temperature of 37.8/100.0, cough or sore throat, an no other good explanations for the symptoms). For most people it will pass, eventually. For some, it will damage the lungs making them susceptible to bacterial infections like pneumonia, which can be fatal.
Last season saw the emergence of a new strain if influenza A, now called 2009 A H1N1, probably due to antigenic shift. It rapidly became pandemic, affecting especially younger people who seemed to have little immunity for the new strain. (Also, pregnant women died at an alarming rate.) In a normal season, it’s the elderly and people with chronic diseases who suffer the worst effects of the epidemic. There is no indication of a looming pandemic this year (although H1N1 will still probably be around), so we’re likely to have the usual unpredictable flu season. Excess deaths due to the flu vary considerably from season to season, with best estimates of between about 3000 and 49000 deaths per year.
Each season, a vaccine is developed by tracking strains emerging in other parts of the world. The vaccine is usually quite effective at preventing flu and complications from flu, but some past seasons have seen new strains emerge after the development of the vaccine. Vaccination is still the best way to prevent flu.
Anti-viral medications can help reduce the severity of the flu, but they’re not terribly effective. Prevention is the best tool we have, including hand washing and other hygiene, and vaccination.
So far, only minimal flu activity has been seen in the US. I’ve seen a few suspicious cases, but nothing confirmed. Each year is a bit of a surprise. I’ve gotten my shot, as has my daughter. Supplies are good this year. Hopefully, it will be a boring season.