Flu season is taking off in the U.S. Over the last 2 weeks, I've seen an increasing number of feverish, achy, glassy-eyed patients testing positive for influenza A, most of whom were not vaccinated. My experience tracks well with the CDC's flu surveillance. Vaccinations were available early enough this year that I've been able to give shots to many patients in time. Unfortunately, the CDC is reporting that so far, this year's vaccine is not a great match for the flu that is going around.
But what does this mean?
First, the news is not all bad. Usually, even “bad” flu vaccines provide some protection. But let's get into some of the details.
Each year, epidemiologists follow the influenza virus as it makes its way around the globe. This surveillance has been very good over the years, but once in a while there is a gap in coverage. Most flu vaccines cover three strains of flu, often two strains of flu A and one of flu B (there is another shot that has a second B strain). (“Strain” is used here as it is commonly understood. The more specific and accurate ways of referring to flu types and subtypes is left for your further reading.) The last several years, the dominant strain has been A, but there are many different types of flu A.
Influenza A types are named based on the types of proteins they carry: hemagglutinin (H) and neuraminidase (N). The flu pandemic in 2009 was caused by a type A(H1N1). So far this year, an A(H3) virus is winning the fight. Of the 85 samples that have been tested so far, 48% are the H3N2 included in this year's vaccines, but the rest are similar to H3N2 subtypes that were not included in this year's shots.
While concerning, this is not a disaster. First, very few samples have been tested so far. As the season progresses we'll have more data to make judgments. If the current trends hold (and there's no guarantee), the flu shot still covers nearly half the circulating viruses very well, and probably offers partial protection against the rest. Even with the “mismatch,” the flu shot still offers significant protection.
If you haven't yet gotten your flu shot, get to it. There's no down side, and the protection, while not perfect, might still save you weeks of misery, and perhaps even your life.
Peter A. Lipson, ACP Member, is a practicing internist and teaching physician in Southeast Michigan. After graduating from Rush Medical College in Chicago, he completed his internal medicine residency at Northwestern Memorial Hospital. This post first appeared at his blog at Forbes. His blog, which has been around in various forms since 2007, offers "musings on the intersection of science, medicine, and culture." His writing focuses on the difference between science-based medicine and "everything else," but also speaks to the day-to-day practice of medicine, fatherhood, and whatever else migrates from his head to his keyboard.