Influenza and the weather

By: Dr. Jeff Masters , 1:14 PM GMT on May 04, 2009

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It is well known that influenza hits hardest in winter--November to March in the Northern Hemisphere, and May to September in the Southern Hemisphere. In fact, the name influenza comes from the Italian word influenza, meaning "influence"--referring to the "influence of the season" (winter) in causing the illness. In the tropics, where there is little change in seasons, influenza occurs year-round (though increased incidence has been noted in rainy seasons--Viboud et al., 2006). Do the cold temperatures and lower humidities of winter cause increased transmission of the flu virus? If so, why is the current H1N1 swine flu outbreak doing so well, now that it is May, traditionally the end of flu season in the Northern Hemisphere? Or could it be that indoor crowding, lack of sunlight lowering vitamin D levels, and a more depressed immune system in winter are largely responsible, as some researchers have suggested?

Flu infections increase under cold or dry conditions
To test these hypotheses, researchers at the Mount Sinai School of Medicine in New York did a study in 2007 that looked at flu transmission among guinea pigs, which are highly susceptible to human influenza and easily transmit the virus to other guinea pigs (Lowen et al., 2007). The animals were placed in adjacent cages, so that infections could occur by airborne transmission, but not by direct contact (guinea pig lovers will be happy to know that the influenza virus-infected guinea pigs did not display detectable symptoms of disease--weight loss, fever, sneezing, and coughing--during the experiments). By carefully controlling temperature and humidity, the scientists were able to study the effects of each. They found that the animals shed much more of the virus--and over a longer period of time--at cold temperatures, which led to increased infection rates. The animals' immune system showed no signs of stress from the cold weather, arguing against the idea that cold conditions lead to increased infections by lowering the immune system. Lower humidities were also found to increase flu transmission rate, though the variation of infection rate with humidity was more complicated. The scientists built a model (Figure 1) to fit the data, and proposed that lower humidity increased infection rates through two mechanisms:

1) The stability of influenza virons in the suspended aerosol particles infected creatures cough out is dependent upon the humidity. Viruses are most stable at low RH (20%-40%), least stable at intermediate RH (50%), and stable again at high RH (60%-80%) (Schaffer et al., 1976). Thus, the virus has better staying power at the low moisture levels typical of winter.

2) At high RH (80%), exhaled respiratory droplets grow quite large as water vapor condenses around them, and these drops quickly settle to the ground under the force of gravity. Thus, even though the virus is stable at high humidities, it settles out of the atmosphere quickly, and cannot contribute to influenza virus spread.


Figure 1. A model of influenza transmission rates at 68°F (20°C) (dashed line) and 41°F (5°C) (solid line), as a function of relative humidity. Transmission efficiency is highest at low relative humidity, when influenza virions in an aerosol are relatively stable, and exhaled respiratory droplets stay small and don't settle out under the force of gravity. Transmission is diminished at intermediate humidity when virus particles are relatively unstable, but improves in parallel with influenza virus stability at higher humidities. At high humidity, evaporation from exhaled particles is limited, respiratory droplets settle out of the air, and transmission is blocked. At cold temperatures (solid line), transmission is more efficient than at warm temperatures (dashed line), but is reduced to a rate of 50% at higher humidities. Image credit: Lowen, A.C., S. Mubareka, J. Steel, and P. Palese, 2007, "Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature", PLos Pathogons, October 2007.

The researchers found no guinea pig infections at 86°F (30°C), which implies that in tropical climates, people may transmit the virus by direct contact rather than by coughing and sneezing. A second study Lowen et al., 2009) confirmed this idea--at least among guinea pigs. The authors concluded, "To our knowledge, we demonstrate for the first time that cold temperatures and low relative humidity are favorable to the spread of influenza virus. Although other factors likely contribute to the periodicity of influenza epidemics, it is clear that air temperature and RH could play an important role. Influenza virus transmission indoors could potentially be curtailed by simply maintaining room air at warm temperatures (>20 °C) and either intermediate (50%) or high (80%) RHs".

Climate change and influenza
The results of this study imply that global warming may significantly reduce influenza world-wide, since a warmer climate will also be more humid. Typically, there are between three and five million cases of severe flu and up to 500,000 deaths worldwide each year. In the United States alone, an average of 41,400 deaths and 1.68 million hospitalizations are attributed to influenza each year. A warmer world should reduce these numbers, if the current research is correct. However, these gains must be balanced against the possibility that malaria will become more widespread in a warmer world, since malaria kills about one million people per year.


Figure 2. Combined flu and pneumonia deaths in the United Kingdom during the great 1918 flu pandemic showed that the flu had three distinct peaks: one in June - July (a relatively mild form of the disease), followed by an extremely deadly outbreak in October, then another during the winter of 1918 - 1919. The 1918 flu pandemic infected 1/3 of the world's population, killing 50 - 100 million people. Strangely, the October peak occurred almost world-wide, with Bombay, India and Boston, Massachusetts peaking the same week. Image credit: Jordan, E., "Epidemic influenza: a survey", Chicago: American Medical Association, 1927.

Flu pandemics show little seasonality
The current Mexican H1N1 swine flu outbreak is seemingly unusual, since it is hitting at the end of the traditional flu season, in April - May. However, when a new flu strain develops that humans have no immunity to, the new strain is less constrained by seasonality. According to Dr. Jeffery Taubenberger, the virologist who helped isolate the genetic code of the virus responsible for the great 1918 flu pandemic, "Historical records since the 16th century suggest that new influenza pandemics may appear at any time of year, not necessarily in the familiar annual winter patterns of inter-pandemic years, presumably because newly shifted influenza viruses behave differently when they find a universal or highly susceptible human population." Indeed, the 1918 flu pandemic reached its peak in September - October (Figure 2), and the most recent flu pandemic, the 1968 Hong Kong flu, began in July. It wouldn't surprise me if the current flu outbreak dies down in the Northern Hemisphere over the summer months, as the combined effects of high temperatures, higher humidities, less indoor crowding, and increased sunlight interfere with its spread. However, we need to be ready for the virus to reappear in the Fall--potentially in a mutated, more virulent form--such as occurred during the 1918 flu pandemic.

References
Lowen, A.C., S. Mubareka, J. Steel, and P. Palese, 2007, "Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature", PLos Pathogons, October 2007.

Lowen, A.C., S. Mubareka, J. Steel, and P. Palese, 2009, "High Temperature (30°C) Blocks Aerosol but Not Contact Transmission of Influenza Virus", Journal of Virology, June 2008, p. 5650-5652, Vol. 82, No. 11 0022-538X/08/$08.00+0 doi:10.1128/JVI.00325-08

Schaffer, F.L., M.E. Soergel, and D.C. Straube, 1976, "Survival of airborne influenza virus: effects of propagating host, relative humidity, and composition of spray fluids", Arch Virol 51: 263-273.

Viboud, C, W.J. Alonso, and L. Simonsen, 2006, "Influenza in tropical regions", PLoS Med 3: e89 doi:10.1371/journal.pmed.0030089.

Vitamin D and influenza links:
http://www.medicalnewstoday.com/articles/51913.ph p
http://www.sciencedaily.com/releases/2008/08/0808 11195629.htm
http://www.vitamindcouncil.org/science/research/v itamin-d-and-influenza.shtml

Jeff Masters

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Quoting presslord:


well...actually...you, orca and Tampa are OK by me...which really doesn't speak so well for y'all...


Presslord you must be a Troll also with those kind words........LOL
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Quoting SevereHurricane:
Florida Derecho 1993

Photobucket


I'm dying for that right now

It is too dry here
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Quoting Ossqss:


I am guessing you are talkin about Orca, no, no, Tampa, no no, Aaaahh ME! I got it and I resemble that remark :)

I use a rule of thumb,

If you don't give someone the power to bother you, they can't.

Or the ignore button, which BTW, don't ever test that feature by placing yourself on it


Oh man.. what did I do this time :(
I wasn't even here?
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Quoting melwerle:
585 - troll season - i wonder if GA folks actually need a permit for troll spray.

586. Ok...THAT was funny - has someone actually tried to put themselves on the ignore list? Sounds like something I would do accidentally. After a scotch and a rain dance (which btw, it is raining nicely here, thank you magic ingrediant!)


Mel, it worked !

93 weather event put 11.5 inches of rain in my back yard in 8 hrs. Never seen so many fire ants and snakes making their way to higher ground, which was my garage !
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The GFS is the best (I consider) at forecasting shear. Shear can be forecasted months in advance.

Shear forecasting has gotten better, and yes, a general shear pattern for a large area can be forecasted months in advance with a degree of uncertainty.
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585 - troll season - i wonder if GA folks actually need a permit for troll spray.

586. Ok...THAT was funny - has someone actually tried to put themselves on the ignore list? Sounds like something I would do accidentally. After a scotch and a rain dance (which btw, it is raining nicely here, thank you magic ingrediant!)
Member Since: June 28, 2006 Posts: 12 Comments: 1837
Quoting Ossqss:


I am guessing you are talkin about Orca, no, no, Tampa, no no, Aaaahh ME! I got it and I resemble that remark :)

I use a rule of thumb,

If you don't give someone the power to bother you, they can't.

Or the ignore button, which BTW, don't ever test that feature by placing yourself on it


well...actually...you, orca and Tampa are OK by me...which really doesn't speak so well for y'all...
Member Since: Posts: Comments:
Florida Derecho 1993

Photobucket
Member Since: September 7, 2008 Posts: 17 Comments: 1604
Quoting presslord:
Drak has forgotten more than you'll ever know....go play elsewhere....


I am guessing you are talkin about Orca, no, no, Tampa, no no, Aaaahh ME! I got it and I resemble that remark :)

I use a rule of thumb,

If you don't give someone the power to bother you, they can't.

Or the ignore button, which BTW, don't ever test that feature by placing yourself on it
Member Since: Posts: Comments:
It is great to see Drak back! Agree with Mel and I too gasp at the insults to Drak! Season must be upon us as the trolls are appearing!
Member Since: June 11, 2008 Posts: 24 Comments: 5910
Good viewing on Redoubt.

Member Since: August 19, 2008 Posts: 6 Comments: 2490
Gasps at the insult to drak...
Member Since: June 28, 2006 Posts: 12 Comments: 1837
Drak has forgotten more than you'll ever know....go play elsewhere....
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Quoting TampaSpin:


Thanks for keeping that too yourself......LOL!


You didn't know? I have seen her swimming in our pool.. trust me.. she is a she
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Quoting KEHCharleston:
Ana will form just north west of Jamaica on May 23.First of October, I think. Very, very excited.


Excellent about Destin!!!! Will buy Anna futures based on your recommendation....
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Quoting cdo:
Drak has always had a issue with keeping his Ego in check...remember when he started on this site he was in middle school.


I've always had an issue with trolls too. You're no exception.
Member Since: October 28, 2006 Posts: 57 Comments: 29887
Ana will form just north west of Jamaica on May 23.
Quoting presslord:
Tampa....WU mailll...


KEH....When are ya goin' to Destin?
First of October, I think. Very, very excited.
Member Since: August 19, 2008 Posts: 6 Comments: 2490
thanks for the derecho info - when i looked it up earlier, it looked like trouble but everything seemed to be going a bit to their east. Their weather folks on tv had said they were in for it. Had no idea what it was except for looking it up on wilkepedia - thanks for the info.
Member Since: June 28, 2006 Posts: 12 Comments: 1837
Are you sure Drak Graduated from middle school.......LOL....Just kidding.
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Quoting Drakoen:


No. Just on AEW. Not trying to upstage you, if anything just to add to what you have said and make comparisons. I like challenging people that know what they are talking about. I'm sorry if it comes off as being egotistical, but I mean well.
you can make one strive to gather knowledge its all good
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting TampaSpin:


Thanks for keeping that too yourself......LOL!


No problem LOL
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Quoting hahaguy:


LOL. I had a hunch that keh was a she.


Thanks for keeping that too yourself......LOL!
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Tampa....WU mailll...


KEH....When are ya goin' to Destin?
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Quoting TampaSpin:


eeeekkkkksss......i always thought she was a he......opps!


LOL. I had a hunch that keh was a she.
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Quoting TampaSpin:


eeeekkkkksss......i always thought she was a he......opps!
: )
Member Since: August 19, 2008 Posts: 6 Comments: 2490
Quoting Ossqss:
KEH, don't forget to include solar weather or lack there of, volcanos, and swine flu in that calculation this year :)
Got it - all factored in. Hmmm... there was that deep hot spot in the Atlantic, just about where an underwater volcano sits (sigh) back to the drawing board. ; )

Press, Me too. Always good to see you. Met Michelle. I gotta believe she is a cousin.
Member Since: August 19, 2008 Posts: 6 Comments: 2490
Quoting presslord:
Don't let her fool ya, boys! KEH is pretty darned smart for a girl....


eeeekkkkksss......i always thought she was a he......opps!
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KEH....sorry I missed ya Sat....
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QS
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KEH, don't forget to include solar weather or lack there of, volcanos, and swine flu in that calculation this year :)
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Hey there press, How goes it?
Member Since: August 19, 2008 Posts: 6 Comments: 2490
Don't let her fool ya, boys! KEH is pretty darned smart for a girl....
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Quoting GeoffreyWPB:
Not at all...there will be different opinions on different systems that develop and I look forward to reading all opinions and observations. I respect everyone’s observations.


Same here I usually like to hear everyone's opinion about the tropics.
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Drak, Ossqss
Thanks.

I know that I am a complete neophyte when it comes to weather topics (and that is not apt to change much). However, with what I do know, I thought I might hazard a guess as to where and when for first named storm.
Just considering SAL and wind shear into the picture.
Member Since: August 19, 2008 Posts: 6 Comments: 2490
Not at all...there will be different opinions on different systems that develop and I look forward to reading all opinions and observations. I respect everyone’s observations.
Member Since: September 10, 2007 Posts: 0 Comments: 10976
KEH, was it you looking for Sahara stuff? Just popped in and gone again.

Link
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Quoting KEHCharleston:
What is the best way/model etc to determine wind shear (as pertains to inhibiting tropical storms in the Atlantic)
How far ahead can wind shear be forecasted?


The GFS is the best (I consider) at forecasting shear. Shear can be forecasted months in advance.
Member Since: October 28, 2006 Posts: 57 Comments: 29887
Quoting GeoffreyWPB:
Instead of Iron Chef, this season will be Iron Meteorologist…..who will rain supreme?


LOL. Let's not stir the pot. Avoid crossing the Rubicon while we still can.
Member Since: October 28, 2006 Posts: 57 Comments: 29887
Instead of Iron Chef, this season will be Iron Meteorologist…..who will rain supreme?
Member Since: September 10, 2007 Posts: 0 Comments: 10976
What is the best way/model etc to determine wind shear (as pertains to inhibiting tropical storms in the Atlantic)
How far ahead can wind shear be forecasted?
Member Since: August 19, 2008 Posts: 6 Comments: 2490
Quoting Twinkster:
I am taking 3 AP classes over the next two weeks

AP English Literature
AP Macroeconomics
AP Human Geography



next year I am taking
AP English Language
AP US History
AP Microeconomics
AP US Government
AP Biology
anbd then I have IB courses
IB Calculus
IB Economics


That's a lot to be taking. That will be very overwhelming to you; nevertheless, good luck.
Member Since: October 28, 2006 Posts: 57 Comments: 29887
Quoting Weather456:
I think this is the first area that you have speculated that I actually agree with based on my own observations.

Your making it sound as if I speculated the world of areas. I am surprise you agree with me because ever since I return, your trying to upstage me every chance you get even on my own blog. I do not know about your meteorological background but I have been working hard for years to build up mines so most of the time I know what I'm talking about and other times I'm wrong. I'm not upset or angry though, just stating an observation.


No. Just on AEW. Not trying to upstage you, if anything just to add to what you have said and make comparisons. I like challenging people that know what they are talking about. I'm sorry if it comes off as being egotistical, but I mean well.
Member Since: October 28, 2006 Posts: 57 Comments: 29887
Blog Refresh
Mirror Site

Daily Area of Interest
Click to enlarge
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Canucks 3 others 1
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Quoting natrwalkn:
Post 527.

I was talking about a completely different storm.
Member Since: June 9, 2007 Posts: 4 Comments: 15776
Post 527.
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Quoting natrwalkn:
538 That's not the storm that was being asked about. Stop trying to confuse everyone.


What are you talking about? Im pretty sure he was asking about my image.
Member Since: June 9, 2007 Posts: 4 Comments: 15776
Cant forget about the Subtropical Derecho event from the Superstorm of 93

Member Since: June 9, 2007 Posts: 4 Comments: 15776
538 That's not the storm that was being asked about. Stop trying to confuse everyone.
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Storm Relative Velocity shows some pretty strong rotation.

Member Since: June 9, 2007 Posts: 4 Comments: 15776

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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