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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544. Stormchaser2007
1:11 AM GMT on May 06, 2009
Storm Relative Velocity shows some pretty strong rotation.

Member Since: June 9, 2007 Posts: 4 Comments: 15776
543. GeoffreyWPB
1:10 AM GMT on May 06, 2009
Just a reminder...when the season is upon us and your area is threatened...remember this blog is mainly opinions and assumptions...Please stay tuned to your local authorities for official information....That being said, I am looking forward to some spirited debates between the more adept and knowledgeable bloggers here.
Member Since: September 10, 2007 Posts: 0 Comments: 10975
542. KEEPEROFTHEGATE (Mod)
1:10 AM GMT on May 06, 2009
Quoting melwerle:
ok - might have gotten lost in the shuffle of the blog this evening - a friend in the zip of 39154 just wrote me on our regular email - said that the weather folks are saying they are expecting a derecho (?) - anything she should know or what to do to prepare. It's getting dark there and she has a bunch of rescue dogs that she fosters and getting a bit concerned. Any assistance? Planning ahead of time?

straight line winds are a min of 93 kmh and can be as high as 200 kmh but rare short lived maybe 5 to 10 mins the most as it passes wind driving rains along with it remove any loose items around home secure any thing that can be damaged by wind thats about it get ready to ride out the storm as it approaches at night it is harder to see the advancing gust front so there will be little warning before arrival except you may notice wind shift but winds will pick up very fast with the shift so its not much of a warning
Member Since: July 15, 2006 Posts: 169 Comments: 53296
541. KEHCharleston
1:08 AM GMT on May 06, 2009
Quoting Twinkster:
does anybody have a link to that map that shows the saharan dust off of africa
There is also this link. Not specifically for only Saharan Dust. Would like some feedback from those of you in the know. Useful or not?
Member Since: August 19, 2008 Posts: 6 Comments: 2490
540. Ossqss
1:07 AM GMT on May 06, 2009
Here is a Derecho from 1998, that thing was cookin.

Member Since: June 12, 2005 Posts: 6 Comments: 8185
539. Patrap
1:07 AM GMT on May 06, 2009
Roger that,..

NEXRAD Radar
Abilene, Base Reflectivity 0.50 Degree Elevation Range 124 NMI

TVS noted too..

Member Since: July 3, 2005 Posts: 421 Comments: 127550
538. Stormchaser2007
1:06 AM GMT on May 06, 2009
Quoting Patrap:
A location would help with that image..

( Most of us cant read minds yet )


Was just about to add that.

Its south west of Mineral Wells, Texas.

Member Since: June 9, 2007 Posts: 4 Comments: 15776
537. natrwalkn
1:04 AM GMT on May 06, 2009
536 South Southeast of Jackson, MS. TWC weather page has really good local radar maps.
Member Since: August 14, 2008 Posts: 0 Comments: 67
536. Patrap
1:01 AM GMT on May 06, 2009
A location would help with that image..

( Most of us cant read minds yet )
Member Since: July 3, 2005 Posts: 421 Comments: 127550
535. Stormchaser2007
1:01 AM GMT on May 06, 2009
Pretty strong HP supercell with some decent rotation located south of Mineral Wells,TX.

Member Since: June 9, 2007 Posts: 4 Comments: 15776
534. futuremet
1:00 AM GMT on May 06, 2009
Quoting Ossqss:


Yes Sir Futuremet, the working world was not exactly what I expected, it was actually fun too, but not the same type. That 60 credit hr class was not an elective and did not change every 9 weeks, or was that marrage? Then responsibility, loans, bosses, goals, or was that marrage too ? Now I am confused.

That's it ! I am going back to school :)


cut to the chase

Life sucks! lol
Member Since: July 19, 2008 Posts: 43 Comments: 4051
533. Patrap
12:59 AM GMT on May 06, 2009


Dupage Severe Weather Warnings Page
Member Since: July 3, 2005 Posts: 421 Comments: 127550
532. Patrap
12:58 AM GMT on May 06, 2009
This is the Line Moving outta Ark,towards N. Miss and Tenn


NEXRAD Radar
North Little Rock, Base Reflectivity 0.50 Degree Elevation Range 124 NMI
Member Since: July 3, 2005 Posts: 421 Comments: 127550
531. Ossqss
12:56 AM GMT on May 06, 2009
Link

I believe this wiki item has clickable loop of the one over the great lakes some time back.
Member Since: June 12, 2005 Posts: 6 Comments: 8185
530. natrwalkn
12:54 AM GMT on May 06, 2009
527 Get ready for some very high sustained winds. Derecho is a very strong, straightline, sustained wind from a strong thunderstorm line. Dr. Greg Forbes on TWC talks about them often.
Member Since: August 14, 2008 Posts: 0 Comments: 67
529. Patrap
12:53 AM GMT on May 06, 2009
There is NO derecho in that area,nor anywhere I can find.

The Local weather in that area
Local wu-info page

National Nexrad Radar



National Watches and Warnings Map,Wu
Member Since: July 3, 2005 Posts: 421 Comments: 127550
528. Ossqss
12:52 AM GMT on May 06, 2009
Quoting futuremet:



lol are you sure?



Yes Sir Futuremet, the working world was not exactly what I expected, it was actually fun too, but not the same type. That 60 credit hr class was not an elective and did not change every 9 weeks, or was that marrage? Then responsibility, loans, bosses, goals, or was that marrage too ? Now I am confused.

That's it ! I am going back to school :)
Member Since: June 12, 2005 Posts: 6 Comments: 8185
527. melwerle
12:50 AM GMT on May 06, 2009
ok - might have gotten lost in the shuffle of the blog this evening - a friend in the zip of 39154 just wrote me on our regular email - said that the weather folks are saying they are expecting a derecho (?) - anything she should know or what to do to prepare. It's getting dark there and she has a bunch of rescue dogs that she fosters and getting a bit concerned. Any assistance? Planning ahead of time?
Member Since: June 28, 2006 Posts: 12 Comments: 1837
526. futuremet
12:46 AM GMT on May 06, 2009
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.


My forecast was busted by a mesoscale event about 2 months ago lol. I will never let it happen again
Member Since: July 19, 2008 Posts: 43 Comments: 4051
525. Cavin Rawlins
12:43 AM GMT on May 06, 2009
Quoting Twinkster:
does anybody have a link to that map that shows the saharan dust off of africa


LINK


OR

LINK
Member Since: July 24, 2005 Posts: 407 Comments: 19076
524. Patrap
12:42 AM GMT on May 06, 2009
Quoting Twinkster:
does anybody have a link to that map that shows the saharan dust off of africa



Saharan Air Layer Analysis
Member Since: July 3, 2005 Posts: 421 Comments: 127550
523. Twinkster
12:41 AM GMT on May 06, 2009
does anybody have a link to that map that shows the saharan dust off of africa
Member Since: June 7, 2007 Posts: 4 Comments: 937
522. Patrap
12:39 AM GMT on May 06, 2009
WAVETRAK - Tropical Wave Tracking


Latest Vorticity

Member Since: July 3, 2005 Posts: 421 Comments: 127550
521. Twinkster
12:38 AM GMT on May 06, 2009
and then senior year I am taking more AP and IB classes

I am hoping to get first year and a half or 2 years of credits done so i can go right to my major
Member Since: June 7, 2007 Posts: 4 Comments: 937
520. futuremet
12:38 AM GMT on May 06, 2009
517

I can do it but it requires too much dedication

good luck during 6 hours of homework every day...SIGH
Member Since: July 19, 2008 Posts: 43 Comments: 4051
519. Cavin Rawlins
12:37 AM GMT on May 06, 2009
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.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
518. futuremet
12:37 AM GMT on May 06, 2009
Quoting Ossqss:
Congrats on the all the higher education successes!!! Work hard and enjoy the ride and success will follow. The definition of luck is when hard work meets opportunity.

It has been 20+ years since I got my degrees and I really miss that time in my life.

I think I have socks older than some of you. Yikes ! :)




lol are you sure?

Member Since: July 19, 2008 Posts: 43 Comments: 4051
517. Twinkster
12:37 AM GMT on May 06, 2009
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
Member Since: June 7, 2007 Posts: 4 Comments: 937
516. Ossqss
12:36 AM GMT on May 06, 2009
Congrats on the all the higher education successes!!! Work hard and enjoy the ride and success will follow. The definition of luck is when hard work meets opportunity.

It has been 20+ years since I got my degrees and I really miss that time in my life.

I think I have socks older than some of you. Yikes ! :)

Member Since: June 12, 2005 Posts: 6 Comments: 8185
515. futuremet
12:32 AM GMT on May 06, 2009
Quoting Drakoen:


Good Luck. Those are two tough courses. Try to aim for a 4 or 5. That's what most colleges accept. Have you already taken AP Enviro?


I was happy after scoring a 4 for AP World history last year; I am trying to see if I can do it again this year. I know for a fact that I will pass AP U.S history, since it only requires general knowledge. AP ENG however, overwhelms me with these numerous sententious rhetorical strategies lol. So I am devising a strategy to pass it.

I will take AP physics next year, not AP Environmental science. I think it is boring--it talks to much about pollution, and Global warming (pseudoscience). I would like it more if it focused more on meteorology.

AP physics can really be beneficial to me

It is the only AP class I am taking next year
Member Since: July 19, 2008 Posts: 43 Comments: 4051
514. Patrap
12:26 AM GMT on May 06, 2009
Hurricane Hunter plane will offer tours at ILM

Published: Tuesday, May 5, 2009 at 5:20 p.m.
Last Modified: Tuesday, May 5, 2009 at 5:20 p.m.

One of the world-famous “Hurricane Hunter” aircraft that fly into tropical storms with high-tech instruments to gauge their strength and potential track is coming to the Wilmington International Airport.
Member Since: July 3, 2005 Posts: 421 Comments: 127550
513. natrwalkn
12:24 AM GMT on May 06, 2009
511 I've always loved that song!! Thanks
Member Since: August 14, 2008 Posts: 0 Comments: 67
512. Drakoen
12:22 AM GMT on May 06, 2009
Quoting futuremet:


two

AP English Language and U.S


Good Luck. Those are two tough courses. Try to aim for a 4 or 5. That's what most colleges accept. Have you already taken AP Enviro?
Member Since: October 28, 2006 Posts: 57 Comments: 29887
511. Patrap
12:21 AM GMT on May 06, 2009


Schools out for Summer
Member Since: July 3, 2005 Posts: 421 Comments: 127550
510. natrwalkn
12:20 AM GMT on May 06, 2009
Thanks everyone!!
Member Since: August 14, 2008 Posts: 0 Comments: 67
509. futuremet
12:19 AM GMT on May 06, 2009
Quoting Drakoen:


How many do you have?


two

AP English Language and AP U.S History
Member Since: July 19, 2008 Posts: 43 Comments: 4051
508. Cavin Rawlins
12:19 AM GMT on May 06, 2009
Quoting natrwalkn:
Finished all my exams yesterday, grades were all posted today. Graduating from UNC-Wilmington with a BA in Physical Geography and a 3.5 GPA. Commencement this Saturday. On to grad school to do some SERIOUS climatology research!!! WHOPEEEEE!!!!!!!


Congrats from one graduate to the next. I cannot wait for mines in July.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
507. natrwalkn
12:18 AM GMT on May 06, 2009
Quoting futuremet:
502

The next couple of weeks will be tough for me

I have to take AP exams friday and next week. Hopefully I get a 3 or higher to receive college credit...


Good luck!! I know exactly how you feel! Exams are SO stressful, but it's such a relief afterward when you've studied hard, do well, and have them behind you!!
Member Since: August 14, 2008 Posts: 0 Comments: 67
506. Drakoen
12:14 AM GMT on May 06, 2009
Quoting futuremet:
502

The next couple of weeks will be tough for me

I have to take AP exams friday and next week. Hopefully I get a 3 or higher to receive college credit...


How many do you have?
Member Since: October 28, 2006 Posts: 57 Comments: 29887
505. severstorm
12:14 AM GMT on May 06, 2009
502 GREAT JOB good luck and prosper
Member Since: November 25, 2007 Posts: 0 Comments: 956
504. futuremet
12:13 AM GMT on May 06, 2009
502

The next couple of weeks will be tough for me

I have to take AP exams friday and next week. Hopefully I get a 3 or higher to receive college credit...
Member Since: July 19, 2008 Posts: 43 Comments: 4051
503. Drakoen
12:09 AM GMT on May 06, 2009
Quoting natrwalkn:
Finished all my exams yesterday, grades were all posted today. Graduating from UNC-Wilmington with a BA in Physical Geography and a 3.5 GPA. Commencement this Saturday. On to grad school to do some SERIOUS climatology research!!! WHOPEEEEE!!!!!!!


Well done! Good Luck in your endeavors!
Member Since: October 28, 2006 Posts: 57 Comments: 29887
502. natrwalkn
12:08 AM GMT on May 06, 2009
Finished all my exams yesterday, grades were all posted today. Graduating from UNC-Wilmington with a BA in Physical Geography and a 3.5 GPA. Commencement this Saturday. On to grad school to do some SERIOUS climatology research!!! WHOPEEEEE!!!!!!!
Member Since: August 14, 2008 Posts: 0 Comments: 67
501. Drakoen
12:06 AM GMT on May 06, 2009
Quoting Weather456:
I just looked as some meteograms out of Africa, just along the Guinea Gulf coast and each station going west reported a wind shift from NE-SE which is anomalous to the mean SW flow, coinciding with this feature. PV charts and 700 mb also show wind shifts and vorticity maxs. Satellite imagery continues to display wave-like signatures with some turning. This further supports the presence of Africa Easterly Wave. The only other piece if evidence needed is a QuikSCAT pass. Even if this feature is not recognize by the TPC I will still hold strong, the idea.





I think this is the first area that you have speculated that I actually agree with based on my own observations.
Member Since: October 28, 2006 Posts: 57 Comments: 29887
thats not an island :p lol
Member Since: Posts: Comments:
HI everyone from zephyrhills fl. We just got a mess of rain to the tune of 1.60inches in 35 mins. Will not soak in much but it sure will help.
Member Since: November 25, 2007 Posts: 0 Comments: 956
I have a friend who is being told by their weather folks that they are expecting a derecho...

Can someone explain? She is going to be registering here for the first time and asking questions...perhaps someone can provide the info and what she should do...

Thank you, Melissa
Member Since: June 28, 2006 Posts: 12 Comments: 1837
Anybody who has HBO I recommend watching this documentry.
Click Here
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One can Videotape ones Home content's at this time as well for insurance claims...


Hurricane.com since 1994,with more Cane Prep


Member Since: July 3, 2005 Posts: 421 Comments: 127550
good post pat...also remember all you homeowners in prone areas...make sure your H.O. Insurance is up to date and make sure you have loss of use insurance. I learned the hard way after Wilma.
Member Since: September 10, 2007 Posts: 0 Comments: 10975

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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.