May 4, 2009

How Should We Think About the Flu Now?

update written by Avram L. Nemetz, M.D. Medical Director

How should we be thinking about the H1N1 flu, now that it has been longer than 10 days since its existence became known to the public?

The new virus has fully emerged and is spreading person-to-person like a regular seasonal influenza virus, with laboratory confirmation already in 36 states and 20 different countries. There is no medical reason to imagine this spread will fail to continue to progress in the same manner moving forward.

Fortunately, the virus so far continues to cause "mild" illness. It does not harbor particular proteins associated with a high degree of influenza lethality-neither a protein which was present on the 1918 Spanish Flu virus nor a different protein found on the H5N1 Avian Flu virus (which is still lurking in the animal population in Asia).

If you get exposed to the Influenza A H1N1 virus, you can expect to be miserably sick for three days, to miss ten days of work until you have recovered and are no longer contagious, but then to recover with full immunity to subsequent exposure to the virus. Your company would have to deal with the consequences of an on-the-job full-blown influenza panic. You would not personally have to worry about a "second wave" of influenza in the fall. This scenario can be managed, and is not bad for a worst-case imaginable situation.

But there is also misinformation galore spreading around the world. A NY Times article about predicting the spread of flu with the aid of the "Where's George?" dollar bill tracker, well known on the web, became a top most e-mailed story.

It measures the frequency of a certain type of face-to-face interaction, but as model for the spread of disease, it's silly and guaranteed to be inaccurate. The study designers stopped the model after four weeks, but the influenza virus is barely getting started after that short amount of time.

Mexico is claiming to have passed their peak of infection, but this does not mean their epidemic is over. The Northern Hemisphere is ending its flu season, and WHO director Margaret Chan took pains yesterday to note that this could mean that a mild first wave now could be followed by a stronger second wave of flu in the fall, as happened with the 1918 pandemic. She seems concerned that complacency could replace panic as the mildness of the present outbreak becomes apparent.

The Southern Hemisphere is about to enter its own flu season, and may be the source of much of the news about flu over the next 3-4 months.

What does this mean for our more immediate neighborhood? Flu cases soon will no longer be counted case by case, but will look more like the map on the Weather Channel that tracks outbreaks during the flu season. There will be states with no reported flu, and some scattered flu outbreaks in the spring and summer. In the fall and winter the maps likely will fill first with scattered, then moderate, and then widespread outbreaks.

Each seasonal flu year, 10-15% of the US population is infected by the influenza virus. In a season with a new virus emerging to which none of us has immunity, the infection rate could be twice that.