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 zoomiami:
just giving ya'll a hard time - get a kick out of watching the back and forth.


Deb, when is the new update coming out :)
I know you are far to sweet and innocent to join this crowd in picking on me :)
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enter at own risk this has been better than comedy central
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Quoting KEEPEROFTHEGATE:
shep ya beter quit poking at that it may be in your better interest ya dont want to disappear for 24 or more at least i don't think you do


Shep keeps forgetting the golden rule.. don't feed them :)
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just giving ya'll a hard time - get a kick out of watching the back and forth.
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shep ya beter quit poking at that it may be in your better interest ya dont want to disappear for 24 or more at least i don't think you do
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Quoting theshepherd:
"$100 generous? For the best footage of the day? Have you even seen the video?"

No thanks. But, I did see the one where the Hindenburg blew up.
Shucks, too bad the houses were well built and you couldn't show more destruction. Yeah, gotta hate it when a poporatzi' has a bad day.
Do you have any footage of Britney Spears' DUI?

Can I send you a shirt?


Dude, you are so lame, so un-funny and so insulting that I don't even know how to respond to you...except to say that I hope the planet Earth turns into a utopia for you and you alone, where there are no storms, no earthquakes, no wars, no famines, no blizzards, no volcanos, no disease, and no one dies.
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Quoting zoomiami:
hello ---- is this guys night only?


No join in lol
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hello ---- is this guys night only?
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just a little Thundercloud
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Orca is full of them tonight LOL
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"$100 generous? For the best footage of the day? Have you even seen the video?"

No thanks. But, I did see the one where the Hindenburg blew up.
Shucks, too bad the houses were well built and you couldn't show more destruction. Yeah, gotta hate it when a poporatzi' has a bad day.
Do you have any footage of Britney Spears' DUI?

Can I send you a shirt?
Member Since: September 11, 2008 Posts: 9 Comments: 10030
orca your a blast friend
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active in here tonight huh?
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Quoting RTLSNK:


Watching the new bond movie gave me ideas.


OH OH.. she saw it... your toast
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Quoting Orcasystems:


The raven post was priceless.. you made my day :)


Watching the new bond movie gave me ideas.
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Polar bears are too cute!
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OK, I have to stop before I get i trouble.
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guess the guys are hanging out again - what is it you do to chase all the girls away?

Obviously no good weather to talk about (or bad depending on the point of view)
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Quoting KEEPEROFTHEGATE:
whats next daning with polar bears

.
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Quoting RTLSNK:
Hi Guys - having fun with the stir sticks again I see.


Not me.. Shep borrowed KEH's stir stick..
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whats next dancing with polar bears
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Quoting RTLSNK:
Hi Guys - having fun with the stir sticks again I see.


A little too much fun.
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Hi Guys - having fun with the stir sticks again I see.
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lol
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Quoting hahaguy:
Ossqss, at least the Pens won lol.


They did it the hard way, but I like the trend for sure. Nightall
Member Since: June 12, 2005 Posts: 6 Comments: 8183
Quoting theshepherd:
Wade fishing in 4' of murky waters off Captiva?
Have you ever considered filming hurricanes or living with grissly bears? lmao


Fishing with Grizzlies?

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Quoting theshepherd:
Wade fishing in 4' of murky waters off Captiva?
Have you ever considered filming hurricanes or living with grissly bears? lmao


Not murky at all, clear as a bell until the event !
Member Since: June 12, 2005 Posts: 6 Comments: 8183
958...busted!!!
959...duh huh
Member Since: September 11, 2008 Posts: 9 Comments: 10030
Quoting theshepherd:

Maybe that's what it was worth?
Maybe they were being generous?


No, the footage I got that day trumped anything they had at the time.

The brave ones [the younger set] drove around in the storm, but they didn't get anything because a) either they were too late to get the shot or b) never got a shot because the building codes on South Padre Island are awesome and only some roofs, windows and telephone poles were damaged.

$100 generous? For the best footage of the day? Have you even seen the video?
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Ossqss, at least the Pens won lol.
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Quoting Ossqss:


Just check the insurance she has on you prior to departure :P


I noticed that... I have to change some things... worth a lot more dead then breathing.... hmmm
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ther she blows by quick past me the harp i'll aim for the blow hole be fore he gets away
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Quoting Ossqss:


Interesting , I boated next to a 20' Hammerhead the locals called Hitler in that pass several times. That was not fun when you see a shark almost as large as your boat, for sure.

In season, not a good place to swim either ! While wade fishing off of N. Captiva in 4' of water, I watched a shark take out a 5'Tarpon, 10' from me, at high tide. Never looked at that water the same way .
Wade fishing in 4' of murky waters off Captiva?
Have you ever considered filming hurricanes or living with grissly bears? lmao
Member Since: September 11, 2008 Posts: 9 Comments: 10030
Quoting Orcasystems:


Hmmm so Shep was planning on turning me into Shark Bait? I knew he was chatting up SWMBO to much.


Just check the insurance she has on you prior to departure :P
Member Since: June 12, 2005 Posts: 6 Comments: 8183
Quoting theshepherd:
Hey!!! This is a family show...


Umm a Shepard's hook... The Shep?? get it...
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Quoting Ossqss:


Interesting , I boated next to a 20' Hammerhead the locals called Hitler in that pass several times. That was not fun when you see a shark almost as large as your boat, for sure.

In season, not a good place to swim either ! While wade fishing off of N. Captiva in 4' of water, I watched a shark take out a 5'Tarpon, 10' from me, at high tide. Never looked at that water the same way .


Hmmm so Shep was planning on turning me into Shark Bait? I knew he was chatting up SWMBO to much.
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Quoting RTLSNK:


ROFLMAO :)


The raven post was priceless.. you made my day :)
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Quoting Orcasystems:


BF gave it to me.. its almost brand new.. came with a 45 gallon barrel of Halo polish to boot :)

You just jealous because your Staff has a crook in it.

Hey!!! This is a family show...
Member Since: September 11, 2008 Posts: 9 Comments: 10030
been a funny deck tonight thats fer sure
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Quoting theshepherd:
I ain't skeered. When he comes to Fla to visit SF and Rb, I'll take him to Boca Grande Pass and put him on a Tarpon that will drag his ol' Canuck hatrack excuse of a carcass halfway back to the great state of Texas...whew!


Interesting , I boated next to a 20' Hammerhead the locals called Hitler in that pass several times. That was not fun when you see a shark almost as large as your boat, for sure.

In season, not a good place to swim either ! While wade fishing off of N. Captiva in 4' of water, I watched a shark take out a 5'Tarpon, 10' from me, at high tide. Never looked at that water the same way .
Member Since: June 12, 2005 Posts: 6 Comments: 8183
Thundercloud01221991

24 days till we are off and runnin
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TWC - You think those news guys have alot of money...but no. They're flat broke. When I showed them my footage from Dolly in the lobby of the hotel [i.e. transformer / patio deck explosion], they offered me $100 bucks for the footage


Maybe that's what it was worth?
Maybe they were being generous?

Put a shirt on.
Member Since: September 11, 2008 Posts: 9 Comments: 10030
Quoting beell:
i'm afraid i can't do that, Dave...


ROFLMAO :)
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Hey everyone I am back for the hurricane season this year it is less then 1 month away. Will we see any storms in May or June this year stay tuned
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Quoting theshepherd:
Please don't say that. If you only knew how hard he worked on that puppy...


BF gave it to me.. its almost brand new.. came with a 45 gallon barrel of Halo polish to boot :)

You just jealous because your Staff has a crook in it.

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Quoting CaneWarning:


It looks just a little crooked...
Please don't say that. If you only knew how hard he worked on that puppy...
Member Since: September 11, 2008 Posts: 9 Comments: 10030
Quoting Ossqss:

Mr. Oz, all the best in your adventure. You have a game plan and I respect that for sure.



I very much appreciate that. I don't do anything without a plan, especially this particular thing.


Quoting Ossqss:


I would not compare you with the weatherchannel's budget and preparation,...


Good thing, too...because they wouldn't rate against what I do. Here's some real facts for comparison.

TWC - The WeatherChannel can't do HD in a hurricane. Nope. It's their uplink. It can't handle the bandwidth, so they shoot and upload SD.

Me - I shoot HD. Period.

------------------------

TWC - Their on-camera, hurricane weather gear is simply the clothes on their back, a flimsy, shiny plastic jacket and swimmers goggles.

Me - My hurricane weather gear is extensive and expensive.

-----------------------

TWC - You think those news guys have alot of money...but no. They're flat broke. When I showed them my footage from Dolly in the lobby of the hotel [i.e. transformer / patio deck explosion], they offered me $100 bucks for the footage.

ME - What services I perform may entertain at times, may make some laugh...but eventually I'm gonna get the terrifying stuff and that, hopefully, will get some people to evacuate who ordinarily would not consider it. And I do it for free on my own dime.
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Quoting KEEPEROFTHEGATE:
cute
a killer whale is not meant to be cute don't be fooled its a ferious mammal that will trash and bash you to a lifeless bloody pulp
I ain't skeered. When he comes to Fla to visit SF and Rb, I'll take him to Boca Grande Pass and put him on a Tarpon that will drag his ol' Canuck hatrack excuse of a carcass halfway back to the great state of Texas...whew!
Member Since: September 11, 2008 Posts: 9 Comments: 10030
Quoting CaneWarning:


It looks just a little crooked...


Crooked, heck that is dyslexically viscous photoshopping. Yep, kinda real word.

I spelled it right :) Orca nothin personal



Link
Member Since: June 12, 2005 Posts: 6 Comments: 8183
you mean that dented thing above yer head is that yer halo
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About JeffMasters

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