Friday, January 21, 2011

Influenza and the Weather

A little bit of reference material. This also partially answers why influenza is so prevalent in the winter.

Probably unlike in many animal species Influenza in humans is a largely seasonal occurrence. There are a few factors possibly influencing this. A atmospheric scientist (Dr J. Masters) at Weather Underground posted a blog at the beginning of the 2009 H1N1 epidemic that pretty much covers all of these.

That blog is based heavily in a 2007 article titled:

Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature  


This study links relative humidity to droplet stability and temperature to show the influenza virus transmits best under cooler and dryer conditions.

This graph shows the ability of the virus carrying to infect at different relative humidities.


This graph shows the viral shedding over time at two different temperatures. Note longer and sightly increased shedding time at lower temperatures.

In the human world people are obviously also more confined under cooler conditions:

We also observed that, although changes in RH did not affect the kinetics of viral shedding in inoculated guinea pigs, changes in temperature did. At 5 °C and all RHs tested, the intranasally inoculated guinea pigs shed higher titers of virus on days 4, 6, and 8 post-infection; most notably, peak shedding was extended in these animals by 2 d relative to guinea pigs housed at 20 °C.

Although this study used Influenza A/Panama/2007/99 virus (Pan/99; H3N2) later, a study by the same author was posted after the 2009 H1N1 pandemic strain verifying it also behaved similarly.

Transmission of a 2009 pandemic influenza virus shows similar sensitivity to temperature and humidity as an H3N2 seasonal strain

More resources on this topic:



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