“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]
Pondering the thought. What if I was a flu virus? I would live everywhere, yet when conditions are not favorable to me, I would find a home and maybe even procreate while I am there. Conditions will improve and we can move out into the world till next year.
The point of this is to realize, that the conditions of the human body are needed for simple survival. There are factors that the human race are not able to control yet. The virus simply does the same as we do under the same conditions. Simple evolution. It goes as far as to explain how a virus will evolve into different strains. Be very careful, any form of life is capable of this.
Some useful post about flu strikes.
I have flu in hot summer why I have is it normal or harmful
“Don’t Believe Everything You Read About Flu Deaths”
https://www.huffingtonpost.ca/lawrence-solomon/death-by-influenza_b_4661442.html?guccounter=1
Could central heat and air be the culprit? Seems to dry my indoor air… just curious?
Probably mucous is a good carrier and we have a lot of mucus in the winter.
what Dyson said makes more sense then any comment on here!
Unfortunately this doesn’t explain why tempered climate areas can have severe out breaks. Such as recently in California where they may have lower humidity but relatively warm temperatures. The South also has big out breaks in Florida where you have higher humidity and temperatures. Maybe as with other living species bacteria as we know it can adapt and survive in all climates even in space as we have now discovered. This may also be a reason why flu shots can be varied significantly in their effectiveness. This year Canada reported the flu shot effectiveness was at 17%. This is hardly a great statistic and explains people’s lack of confidence in the shot. I think the better solution is to prevent spread by immediately isolating people who have signs of the flu. Even someone with the flu that shows up for work or school can spread the bacteria quickly. Too many trying to tough it out and stay working or parents pushing sick kids out the door is contributing to the spread.
I agree! Keep people segregated until they’re not infectious. If it’s killing people and you’ve got it then stay away from others while you’re sick. People with AIDS aren’t allowed to give it to others without consequences, so why would ppl who knowingly have the flu be allowed to go into public without consequences?
I think you missed the last California law on that one. It’s actually more offensive to get someone’s gender wrong, than knowingly transmitting HIV to someone else…
It doesn’t help that in spite of employers saying they want employees to stay home while sick so as not to spread the virus, flu can be contagious for…what, 7 days from the time it’s contracted (and one day before symptoms show up ) …and most employers might be ok with an employee taking one or two days off but God help you if you want to take a full 7 days in order to protect others & prevent it spreading.
The truth is that people can’t afford to stay home without pay for a week (some viruses can take TWO full weeks before the person is no legal beer contagious) AND employers are not really willing to let them even if they could. It’s unfortunate, but the way our society is, these viruses are just going to keep spreading and killing people every winter. It’s shocking really when we realize that 35-36,000 people DIE every year from the Flu – especially when we realize it could be prevented. I hate to say it, but it would probably be best if the vast majority of people worked from home in winter – I know, not really feasible. Too bad we couldn’t do that and stock up for enough food supples to last the winter.
This is from the CDC. People, please read facts not conspiracy theories!! Big pharmaceutical companies suck, absolutely 99%. However, some of the theories posted here are just completely ridiculous.
Can a flu vaccine give you the flu?
No, flu vaccines cannot cause flu illness. Flu vaccines given with a needle (i.e., flu shots) are currently made in two ways: the vaccine is made either with a) flu viruses that have been ‘inactivated’ (killed) and that therefore are not infectious, or b) using only a single gene from a flu virus (as opposed to the full virus) in order to produce an immune response without causing infection. This is the case for recombinant influenza vaccines.
This is the truth. Many people don’t like the truth. They prefer a load of rubbish about conspiracy theories etc.
Keep on telling the truth though. People like me prefer it!
I think you’ll find that viruses are not actually alive, so what do they actually do to them to create a vaccine?
Not true. Everyone I know that got that so called flu shot became extremely sick with the flu. Many of them haven’t had the flu in years .
Flu shots are BS. The human body can cure it’s self . We are supposed to build immunities to these viruses. Not inject ourselves with last year’s viruses. I have not had the flu in over 20 years and that was when I stopped getting the shot. I probably only had the flu shot 3 times in my life. My mom didn’t make me get it either. I got it a few times when a doctor told me that it was important. No more, no way. No one in my household gets it and none of us get the flu.
Well, that settles it, then. Scheetz has spoken. Forget what all these silly “scientists” have to say. Anecdotal evidence by The Ms. Jennifer Scheetz? Etch it in stone!
Your sacrcastic comment was uncalled for. She was only trying to help expose the truth about the flu shots! I too have never had the flu shot in a very long time, and it did not harm me one bit!
I actually agree with her.
The flu shot gives a person the virus in a small dose with the intent of building immunity. The problem is that they can guarantee that it will be the SAME flu going around that immunities protects against . This season there were multiple types of flu, including a version that transmits between humans and animals.
I have NEVER gotten a flu shot and I have had the flu only twice in my entire life.
You do realize that science and scientists are not perfect in their understanding right? Do you also realize that there are people who benefit monetarily from flu shots that “might” protect you from the flu. And actually, peoples experience tell us that many people get full blown cases of flu FROM taking the flu shot.
And btw, regardless of your opinion, there is no call for being an ass just because you disagree with someone
Sorry * they can’t guarantee *
A lot of people have died. At least 75% have not had flu shots versus 25% who had a shot. This is amount reported in the DFW area.
Please get your facts straight. The CDC counts any and all pneumonia deaths in those >65 in their MMWR stats on flu death. Scare tactics work to spread an agenda of increased profits for government/ Big Pharma. Please educate yourself on the influenza vaccine before you blindly jump on a bandwagon preventing anyone and everyone who disagrees with you the autonomy of declining to have what they view as poison shot into their bodies. I wonder how much women in the workforce (of which I am one) has contributed to the perceived “need” to prevent self limiting childhood illness that confer natural lifelong immunity. We have had numerous mumps outbreaks amid college students WHO HAVE BEEN IMMUNIZED in their youth….seems to be a false sense of security until kids reach an age where benign illness suffered as a child, contracted as an adult can either kill you or make you infertile…..hmmm, efficacious?? For whom?
Look, if I don’t get a Flu shot every year, I’m sick in bed for 2 weeks. Never fails. If I get a shot, I might get a minor cold with a sour throat for a day or 2 and it’s gone Nothing if foolproof. I’ll take what never helps.
we are being had big style……………. flu virus is spread by flu shot uptake and mist………….. every single year i get a weird fluey thing now ,and it all started when they started pushing flushot etc……………. its as clear as day to me……… when i was a child hardly anyone i knew got flu or even too many colds,,,now, ALL winter” every one” almost has some full affliction or some “weird” long lasting thing alike a cold but not or flu but not ( thats the manmade cr#p that was in the shots that the uptakers shed for 14 days or so) people take this shot at different weeks too ,so it goes around and stays quite a while now……………. i wholey doubt warmer climate has anything to do with it… and even in winter when temperatures can drop quite low, i have NEVER heard a Turk or Greek say thy had the flu??? and believe me i do know many and have stayed there alot in winter …………………….. all this silly research ….. waste of time and money.
Although I might agree with you that the flu vaccine is a waste of time and money I might not agree for the same reasons. The 1918 flu that devastated the world was before flu vaccines. Even tho flu vaccines were in effect during the one in the 60’s, still quite a few deaths laid at influenza’s door. I don’t think the vaccine is the sole cause of the virus wreaking havoc as the incidences of havoc predate the vaccinations. I’d place my bets with this author here:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870528/
Another factor was the war. In peace time there would have been better nutrition and perhaps quarantines if there were major outbreaks of illness.
The Spanish Flu of 1918 killed more people from ages 20 to 45 because that age group had BETTER immunity. It caused the body to overly attack it until it burned itself out. Older and younger have weaker immunity. I guess they could “ride the waves” better.
YES YES AND YES I Believe the flu is being worsened as they make flu shots every year, They are the reason for the crazy mutations each year!! I too never have heard so many flu problems when i was a kid, NEVER Its getting worse as they go, big phama wanting to make sure we all get flu shots and put money in their overloaded pockets!! Not to mention the sale of Tamiflu I hate them all
Lot less communication years ago.
Flu has killed a lot of people long before we had flu shots though. That said, it’s possibke imo that it may increase the numbers of people getting sick since it actually GIVES them a small dose of flu virus. The stupid thing about it (imo) is that very often the flu that is going around naturally isn’t even the same version the flu shot is intended to protect against (build immunities for). So then we have multiple types of flus gong around at the same time. I refuse to get flu shots. I have gotten the flu maybe twice in my life, the first as a child and the latest I caught from my husband who works in a large building with tons of exposure to these germs flying about. I honestly think the flu shot is probably doing more harm than good. This season (2018) we have heard of not just the elderly, very young and immune compromised being killed by these nasty viruses, but healthy young adults as well. One Dr said he had never seen a virus replicate so fast ! It killed a fairly young healthy woman within , I believe it was 24-48 hours. She was not an isolated case. Also some have been fighting one infection, only to contract another at the exact same time …so their immune system can’t keep up. It does seem to be getting much worse.
I do tend to get the flu every time I get a flu shot. I don’t get the flu when I don’t get the shot. I sometimes get a cold and its in the winter usually. I have had a cold in the fall or spring. I have not had one in the summer.