“Did you get your flu shot?” If your friends are anything like mine, you heard this question at least a dozen times before Thanksgiving. You probably got your fair share of disdainful looks too, if you answered “No.” But why are we worried about getting the flu shot now and not in May? Why is there a flu season at all? After all, what does a virus living in a host who provides a dependable, cozy incubation chamber of 98°F, care whether it is freezing and snowy outside or warm and sunny? This question has bothered people for a long time, but only recently have we begun to understand the answer.
What is the Flu?
In order to discuss why we have a flu season, we must first understand what the flu is. The flu, also called influenza, is a viral respiratory illness. A virus is a microscopic infectious agent that invades the cells of your body and makes you sick. The flu is often confused with another virus, the common cold, because of the similarity in symptoms, which can include a cough, sore throat, and stuffy nose. However, flu symptoms also include fever, cold sweats, aches throughout the body, headache, exhaustion, and even some gastro-intestinal symptoms, such as vomiting and diarrhea (1).
The flu is highly contagious. Adults are able to spread the virus one day prior to the appearance of symptoms and up to seven days after symptoms begin. Influenza is typically spread via the coughs and sneezes of an infected person (1). Around 200,000 people in the United States are hospitalized each year because of the flu, and of these people, about 36,000 die. The flu is most serious for the elderly, the very young, or people who have a weakened immune system (1).
The Flu Season
The flu season in the U.S. can begin as early as October, but usually does not get into full swing until December. The season generally reaches its peak in February and ends in March (2). In the southern hemisphere, however, where winter comes during our summer months, the flu season falls between June and September. In other words, wherever there is winter, there is flu (3). In fact, even its name, “influenza” may be a reference to its original Italian name, influenza di freddo, meaning “influence of the cold” (4).
A common misconception is that the flu is caused by cold temperatures. However, the influenza virus is necessary to have the flu, so cold temperatures can only be a contributing factor. In fact, some people have argued that it is not cold temperatures that make the flu more common in the winter. Rather, they attest that the lack of sunlight or the different lifestyles people lead in winter months are the primary contributing factors. Here are the most popular theories about why the flu strikes in winter:
1) During the winter, people spend more time indoors with the windows sealed, so they are more likely to breathe the same air as someone who has the flu and thus contract the virus (3).
2) Days are shorter during the winter, and lack of sunlight leads to low levels of vitamin D and melatonin, both of which require sunlight for their generation. This compromises our immune systems, which in turn decreases ability to fight the virus (3).
3) The influenza virus may survive better in colder, drier climates, and therefore be able to infect more people (3).
The Flu Likes Cold, Dry Weather
For many years, it was impossible to test these hypotheses, since most lab animals do not catch the flu like humans do, and using humans as test subjects for this sort of thing is generally frowned upon. Around 2007, however, a researcher named Dr. Peter Palese found a peculiar comment in an old paper published after the 1918 flu pandemic: the author of the 1919 paper stated that upon the arrival of the flu virus to Camp Cody in New Mexico, the guinea pigs in the lab began to get sick and die (4). Palese tried infecting a few guinea pigs with influenza, and sure enough, the guinea pigs got sick. Importantly, not only did the guinea pigs exhibit flu symptoms when they were inoculated by Palese, but the virus was transmitted from one guinea pig to another (4).
Now that Palese had a model organism, he was able to begin experiments to get to the bottom of the flu season. He decided to first test whether or not the flu is transmitted better in a cold, dry climate than a warm, humid one. To test this, Palese infected batches of guinea pigs and placed them in cages adjacent to uninfected guinea pigs to allow the virus to spread from one cage to the other. The pairs of guinea pig cages were kept at varying temperatures (41°F, 68°F, and 86°F) and humidity (20%-80%). Palese found that the virus was transmitted better at low temperatures and low humidity than at high temperatures and high humidity (see Figure 1).
Figure 1 ~ Experimental Setup. Guinea pigs were housed in adjacent cages. Guinea pigs in cage 1 were infected by Palese with influenza. Palese observed how many guinea pigs in cage 2 became infected from the guinea pigs in cage 1 at different temperatures and levels of humidity. B, C) Transmission rates were 100% at low humidity, regardless of temperature. At high humidity, transmission occurred only at the lower temperature.
However, Palese’s initial experiment did not explain why the virus was transmitted best at cooler temperatures and low humidity. Palese tested the immune systems of the animals to find out if the immune system functions poorly at low temperatures and low humidity, but he found no difference in innate immunity among the guinea pigs (5). A paper from the 1960s may provide an alternate explanation. The study tested the survival time of different viruses (i.e. the amount of time the virus remains viable and capable of causing disease) at contrasting temperatures and levels of humidity. The results from the study suggest that influenza actually survives longer at low humidity and low temperatures. At 43°F with very low humidity, most of the virus was able to survive more than 23 hours, whereas at high humidity and a temperature of 90°F, survival was diminished at even one hour into incubation (3).
The data from these studies are supported by a third study that reports higher numbers of flu infections the month after a very dry period (6). In case you’re wondering, this is only the case in places that experience winter. In warmer climates, oddly enough, flu infection rates are correlated most closely with high humidity and lots of rain (6). Unfortunately, not much research has been done to explain these contradictory results, so it’s unclear why the flu behaves so differently in disparate environments. This emphasizes the need for continued influenza research. Therefore, we can conclude that, at least in regions that have a winter season, the influenza virus survives longer in cold, dry air, so it has a greater chance of infecting another person.
Although other factors probably contribute as well, the main reason we have a flu season may simply be that the influenza virus is happier in cold, dry weather and thus better able to invade our bodies. So, as the temperature and humidity keep dropping, your best bet for warding off this nasty bug is to get your flu shot ASAP, stay warm, and invest in a humidifier.
Hannah Foster is a PhD candidate in the Molecules, Cells, and Organisms program at Harvard University.
For more information about the flu, check out this video:
References
1) Medical News Today. What is flu? What is influenza? What are the symptoms of flu? < >[2 November, 2014]
2) Centers for Disease Control. The Flu Season. <http://www.cdc.gov/flu/about/season/flu-season.htm> [2 November, 2014]
3) Elert, E. 2013. FYI: Why is There a Winter Flu Season? Popular Science. <http://www.popsci.com/science/article/2013-01/fyi-why-winter-flu-season> [2 November, 2014]
4) Kolata, G. 2007. Study Shows Why the Flu Likes Winter. New York Times. <http://www.nytimes.com/2007/12/05/health/research/05flu.html?_r=1&> [2 November, 2014]
5) Lowen, A.C., S. Mubareka, J. Steel, and P. Palese. 2007. Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature. PLOS Pathogens. 3(10):e151.
6) Roos, R. 2013. Study: Flu likes weather cold and dry or humid and rainy. University of Minnesota Center for Infectious Disease Research and Policy. <http://www.cidrap.umn.edu/news-perspective/2013/03/study-flu-likes-weather-cold-and-dry-or-humid-and-rainy> [14 November, 2014]
My theory is that in warmer temperatures there are more bacteria and they kill the viruses but in colder temperatures, the bacteria die and viruses flourish.
Perhaps bacteria simply spur the immune system to fend off viruses as in:
https://www.nature.com/news/2011/110314/full/news.2011.159.html
It’s so obvious. It’s the pharmaceutical company’s evil doing. Your health in exchange for their profit. And there’s nothing. I mean, not a shit you can do about it.
That’s right jenny
OR, the corruption of human kind and its evilness for wealth over health is the only reason that we are bombarded with these man made illnesses. The life line of the pharmaceutical empires relies upon human beings being constantly sick and poorly and manufacturing seasons of expected illness is a perfect way to manage production of vaccines and products in relieving symptoms Cures are these companies nightmare. Cure means no income. Why put food in a fridge, because is keeps illness away. Its not really rocket science although thats what these con artists wish you to believe it is. Poor un-intelligent people rely upon geniuses to sort it out rubbish. You are all being lied to, as usual. away.
Actually the guy who says CDC could realse it and also look how some side effect of vaccine are simmallr to illness supposed also humans have meddling with virures for 100 of years in third word countries heard phage therapy
Truthfully, all the viruses are tested and put out as a form of population control. However, some tend to mutate and get out of control. A lot of things go into the antibodies and the take billions of dollars to create. Besides the research and creating they have to have enough to administer. Think about the AIDS virus. They have always had a cure for it! It spread so fast and became an epidemic it is nearly impossible to cure all these people that have contracted it. I believe after a certain stage in the virus the antibody doesn’t help. A virus doesn’t die, it just becomes dormant. Each virus is triggered by something. I believe that the viruses injected in our bodies through childhood vaccinations are still there just haven’t been triggered by anything. Think about Shingles. You can only get it if you had chicken pox. It’s the mutated chicken pox virus. If my body is immune to the virus then how does it mutate into another virus 30+ yrs later? Shit weird if you ask me.
I know it sounds stupid, but the lack of fresh air during the winter? Windows closed 24 hours a day? Well I believe the air becomes toxic. I always leave my window open a crack even at 20 degrees. I got the flu this past summer and I think it was I was exposed to someone that was ill. And where they live windows were shut and air conditioning blasting. My point is I think people get sick in the winter cause they are breathing filtered air from the source of heat. Recycled air is what I call it, cause no fresh air is getting in. Same in the summer were breathing recycled air. My advice if someone in the home gets the flu. Take them somewhere to stay a few hours. And deep clean the entire home with the windows cracked open. And after that just keep at least one window cracked open slightly. Oh I also put all my silverware in boiling water then sanitize them in the dishwasher. Cups , bowls , plates also put in boiling water with a drop of bleach and a couple drops of dawn.
Boiling doesn’t sanitize. It’s actually a form of pasteurization.
Hey Stig, you should go back read the article again. The viruses never die, flu seasons vary on different parts of the earth, i.e. flu season is Dec – Mar in the northern hemisphere and June -Sept in the southern hemisphere. The viruses simply move from person to person all year round, mutating along the way and propagate when the conditions are right in different areas. Someone on earth has the virus every day of the year. The other thing to consider is that as the population of the earth continues to grow and people travel all over the world on a daily basis, the chances of coming into contact with an infected person continue to rise significantly. Your hypothesis that viruses are planted every year is silly. It if that were so, how do you explain flu outbreaks hundreds of years ago before we had the understanding or technology to culture and spread viruses? Or the pharmaceutical companies to profit from treating the ill?
Very interesting comments everyone! I completely agree that people get the virus from other people primarily, but I have always wondered how that very first person gets it every year to start infecting everybody else? Considering that the virus requires a host to survive and it dies if it is not inside a body, it should be erradicated every year once people either recover from the flu or die from it. Where is the virus hiding in the meantime? in animals? flying around? maybe in some labs that we do not know about?
I do believe the virus is planted… I do not know by who or what, but every year is planted, and sometimes there are new kinds like H1N1 that are worse than others. The rationale behind my belief is that a very close friend had a chance to be at a meeting where a major transportation company presented to the company he worked for (pharma) about their great abilities to distribute medications in pandemic cases. They were so proud to say that a big pharma company contacted them to be prepared because they knew a pandemic case was coming very soon and they needed to distribute their antiviral when it hit. The executive said to them: when they called us as H1N1 started to spread we had all of the distribution network to distribute their medication worldwide and we did it very well, so you can rely on us for your own medications. Not only him but the entire group was shocked to hear what this gentleman had just said.
The obligated question is how that big pharma company knew that H1N1 was coming and that it was going to become a pandemic case? Not surprisingly the antiviral reached about $6B dollars in sales that year and since governments started to pile up the medication it has reached about $18B. I just can imagine the great bonuses that executives must have received and many medals to hang as well, but I really hope that whoever created and planted that virus cannot sleep well at night just thinking of the order of magnitude that such action created in the global population, and if they do, then shame on them.
Regarding the flu shot, I have had it once many years ago, and that year I got violently ill 4 times in that season. Any other year I usually get sick once but usually it is pretty mild thankfully. Coindicence? Maybe, but maybe not.
When I used to commute to work using public transit I used to get more sick than other years when I commuted by car or worked from home. But yet again, how does the first case of influenza start every year? If somebody knows please share that light with the rest of us or maybe we should ask that big pharma company to share their magic ball with us.
I stopped getting the cold and flu since i stopped getting a flu jab 2 years ago….
Also stopped drinking tap water….. unless it was boiled over….
As a professional person in the business industry I can testify if there was no flu and other similar illnesses that were man made then the pharmacutical industry would of collapsed along time ago….
KEEP THAT IN MIND