While influenza epidemics occur annually the variation in the timing, peak and magnitude remain a mystery. So far influenza in NYC has been mild. Several surveillance systems are used to gauge the severity of flu season and by any of them either flu hasn’t arrived yet or the strain has not varied much from last season. Outpatient visits for influenza-like illness in NYC are still below the 2.5% threshold and of nearly 1800 lab tests done for flu in the first week of 2012 less than 20 were positive (during peak flu season this can range as high as 15%). Elsewhere in the country the story is much the same with only a few states showing activity, but no hot regions. Most of the circulating strains are the H3-type with smaller proportions of H1 and B; all components of this year’s vaccine. Looking at the world picture there is activity in Northern Africa and Japan, however, in general activity remains low.
It is still a good idea to get a flu shot, especially if you have a chronic illness.
http://gis.cdc.gov/grasp/fluview/main.html
Several of my flu surveillance colleagues and I are in awe of the current flu season. We haven't seen anything like it in our short-ish careers in Epidemiology. Have you? Did we just get lucky and vaccinated the heck out of everyone in a season where H1N1 would have been predominant?
ReplyDeleteNo, this isn't all that unique of a flu season. The timing and severity are a function of the strain, prevailing immunity, vaccine coverage and genetics of both host and pathogen. Its like the number of possible hands in poker. The probability of getting a straight flush is about the same as getting the 2 of spades, 3 of diamonds, 4 of hearts, five of clubs and seven of diamonds.
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