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Summary & Participants

Most of us are familiar with the symptoms of the flu—fever, chills, fatigue, stuffy nose, sore throat. Most of us know that it is caused by the influenza virus. And we all dread it. But just what is the flu? What makes the influenza virus so contagious? Join our panel of experts as they discuss this tiny—and common—villain.

Medically Reviewed On: July 21, 2008

Webcast Transcript

DAVID MARKS, MD: We're talking about influenza virus as if it were one virus. But, really, there are different types within that category.

JASON KENDLER, MD: That's correct. There's influenza-A, influenza-B and influenza-C, all different types of virus. Most of the outbreaks, most of the disease we see in people are from influenza-A or B. Influenza-C is thought to cause a much milder disease.

DAVID MARKS, MD: I've never heard of influenza-C, frankly. We never hear about it in medical school.

JASON KENDLER, MD: Correct.

DAVID MARKS, MD: Is it a problem at all?

JASON KENDLER, MD: It's generally not considered to be clinically significant.

ADAM STRACHER, MD: It's said to cause very mild cold sort of symptoms, almost. But the one that really, influenza-A and B are the ones that really cause human disease, and influenza-A is the one that can cause very severe outbreaks much more commonly than B.

DAVID MARKS, MD: How do we know which influenza type is going to be around each year?

JASON KENDLER, MD: The World Health Organization actually does active surveillance at different sites throughout the world. To try and anticipate, to try and prepare the flu vaccine for the coming season, they look at the most common serotypes of the influenza virus that they see in different cities in the world. Oftentimes the serotypes that we see at the tail-end of the season will be seen the next year. Oftentimes the serotypes that are seen in the southern hemispheres will be found in the northern hemisphere.

DAVID MARKS, MD: What do you mean by "serotype"?

JASON KENDLER, MD: The influenza virus has different proteins, different surface proteins, neuraminidase, hemagglutinins, and these proteins are on the surface of the virus. They help the virus infect cells. These serotypes, or these different proteins on the surface are recognized by the body and are the source of the immunity or immune response to fight off the virus.

ADAM STRACHER, MD: The virus is broken into influenza-A and B for the most part, and then those are also broken down into different types, so that based on these types of proteins, they'll be classified into a different type of influenza-A. And then they're also classified by where they were first discovered. So you may find influenza-A Hong Kong virus, and then another serotype designation. And that sort of tells us what type it is.

DAVID MARKS, MD: You answered my question about the different types. Basically, people from the World Health Organization or the CDC are trying to predict what's going to be coming down the road. Maybe that's why sometimes the vaccine is not as effective. At least it seems not to be as effective some years as opposed to others.

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