If there’s one virus outside of the common cold that most of us have had firsthand experience with, it’s clearly influenza. That alone makes it one virus everyone ought to pay attention to—especially as we end a flu season that started so early, catching many Americans off-guard. Scientists who study the flu are already looking ahead to what the 2013-14 season might hold.
The stakes are high: Every year, this highly unpredictable virus descends on us, costing the U.S. economy roughly $80 billion. This year, in the virus’ predictably unpredictable fashion, influenza hit early and hard. In fact, this season started a full month early—sooner than any other season since 2003. And it’s been a grueling one, with those 65 years and older being especially hit hard.
To put it simply, influenza is a very tricky virus. There are three different types of flu viruses, called A, B, and C. The first two spread in humans every season. Influenza C is also common, but just causes very mild upper respiratory tract infections; there’s no vaccine to protect against influenza C.
That’s easy enough to grasp, right? But then you need to know that influenza A can be separated into different subtypes. What’s more, small changes occur in the different subtypes over the years. These changes are called antigenic shift and antigenic drift.
There are two proteins on the influenza virus, hemagglutinin and neuraminidase, or the “H” and “N” in H5N1 and H1N1 (popularly known as bird flu and swine flu, respectively). These proteins play very different roles: Hemagglutinin allows the virus to attach to the host (in this case, human) cell. Neuraminidase cuts the virus off, essentially telling hemagglutinin to spread the love—to “go viral.” The neuraminidase basically promotes the spread of infection by forcing hemagglutinin to attach to other human cells.
In the process of antigenic shift, the combination of hemagglutinin and neuraminidase on the influenza virus changes, effectively making it a different virus than those we’ve seen in previous flu seasons. To further complicate things, these subtypes (H1N1, H3N8, H5N1, etc.) can change via antigenic drift, which are small changes in the virus over a long period of time. For example, the H1N1 subtype has different variants due to antigenic drift. The new variants eventually become unrecognizable to our immune system, which can’t fight them. Result: We come down with the flu.
Now you understand why we need new flu vaccines every year. The changes that the influenza virus undergoes means that last year’s vaccine may do nothing for the types of influenza circulating this year.
So virologists—the folks who study these and other viruses—are left using research (along with some educated guessing) about what types of influenza are likely to be circulating next flu season so the best possible vaccine can be created to fight it.
Not so easy to do, it turns out. As David Scales, HealthMap’s resident physician explains, influenza’s virology makes vaccine development pretty challenging. A group of scientists organized by the World Health Organization (WHO) into a Global Influenza Surveillance and Response System (GISRS) constantly monitor the behavior of influenza in different species. Their goal: to share their findings with each other and predict which influenza viruses will cause the most sickness in a given year. These scientists meet twice a year—once to predict the influenza season for the Northern Hemisphere and once for the Southern Hemisphere.
In February 2012, the GISRS predicted two influenza A viruses—(A/California/7/2009 (h1N1)pdm09-like virus and A/Victoria/361/2011 (h3N2)-like virus)—and an influenza B virus (B/Wisconsin/1/2010-like virus). As a result, the flu vaccine for the 2012-13 season aimed to protect us against these three types of flu.
Initial estimates from the Centers for Disease Control and Prevention (CDC), said the vaccine was 62 percent effective against the flu. Which means that if you got the vaccine, you’d be 62 percent less likely to get a flu that forces you to go to the doctor. The CDC later revised the effectiveness rate to 56 percent. Though this may seem like an absurdly low rate, predicting what types of flu will attack us is never easy. As Tom Frieden, director of the CDC, stated in a recent press telebriefing: “What we’ve known for a long time is that the flu vaccine is far from perfect. But it’s still by far the best tool we have to prevent the flu.”
The just met in February 2013 to start to figure out what strains we might have to worry about for the 2013-14 flu season in the Northern Hemispher. Among the strains they predict might be in play are Influenza A/California/7/2009 (H1H10pdm09-like virus), A(H3N2) virus, and Influenza B/Massachusetts/2/2012-like virus. Last year, the Food & Drug Administration approved the 2012-2013 flu vaccines for the U.S. in August 2012, so keep an eye out for flu vaccine information in late summer 2013.
To protect yourself for the remainder of this year’s season, check out HealthMap’s Vaccine Finder to see what influenza vaccine is recommended for you and where you can get it. Remember to wash your hands well and often, and to cough or sneeze into your elbow, not your hands.
You can also participate in Flu Near You, a project run by HealthMap of Boston Children’s Hospital, the American Public Health Association, and Skoll Global Threats Fund. Sign up to anonymously submit your flu symptoms (or lack thereof, if you’re well) through a weekly survey and see a map of flu spread in your community and nationwide in near real time.
Did you get the flu this year? Are you worried about next year’s strain?