Types of Flu Viruses

By Dianne Lange. Medically reviewed by Tom Iarocci, MD. May 7th 2016

Whether you call it influenza, the grippe or the dreaded flu, to most people it is just bad news. To professional flu trackers though, like the experts at the Centers for Disease Control and Prevention, knowing the type of influenza virus infecting people throughout the United States is critical to public health.

During flu season, the CDC’s weekly report details the numbers to help health professionals spot flu trends and identify how well the vaccine is working, says Susan J. Rehm, MD, vice chair of the department of infectious disease at Cleveland Clinic and medical director of the National Foundation for Infectious

Rehm says health care professionals can order a rapid influenza diagnostic test to identify the type of virus infecting you. “The results of a flu test may not affect treatment but may be important to know if you’re sick with a flu or some other virus,” says Rehm.

This year, H1N1 is the most common type A virus affecting people, Rehm says, but there are two other types of human flu virus, types B and C. (Interestingly, in addition to swine flu, there’s an avian flu and a bat flu.)

You should get a flu shot every year to protect yourself from new strains of type A and B.

Here’s what’s important to know about each type:

Type A Flu Virus

The CDC distinguishes the subtype of influenza type A viruses by labeling it with an “H” and an “N,” depending on the type of proteins — hemagglutinin and neuraminidase — on its surface.

Currently, there are two subtypes of A viruses that concern humans: The newer type is now simply known as H1N1. It caused the first flu pandemic in half a century in 2009.

People infected with H1N1 become quite sick; even those who are fit and healthy can become ill enough that they need to be hospitalized.

Type A viruses undergo genetic changes over time to produce different strains, and some cause a mild to moderate infection, while others cause serious and even fatal infections.

Type B Flu Virus

There are different strains of type B viruses that have the potential to cause an epidemic. Historically, B viruses cause far fewer cases of seasonal flu than type A. “An infection with type B can still cause a serious infection,” says Rehm. In 2014, there is a new quadrivalent vaccine, which protects against four types of flu: two B viruses and two A viruses.  

Type C Flu Virus

Type C viruses cause a respiratory infection so mild you may never notice any symptoms. Type C strains do not cause epidemics and are not included in flu vaccines. “It’s so under the radar in terms of frequency and severity that the CDC doesn’t even track it,” says Rehm.

Next Steps

  • Medical experts urge everyone age six months and older to get the flu shot.
  • Remember the acronym “FACTS” to recognize when you should be concerned about the flu: “F” for fever, “A” for aches, “C” for chills, “T” for tiredness, and “S” for sudden symptoms. Confirm with your doctor that you do have the flu and not something else. Then, ask if you require antiviral medication to shorten the duration of your symptoms. 

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