The science of flu season

Flu season is in winter. Okay, great. But why? (Consider this an open thread for all your favorite humidifier recommendations.)


  1. I don’t know, but I bet it has a lot to do with human behavior: tending to stay indoors, touch indoor objects more and therefore transmit more disease.

    The other thing I’ve been thinking about is how flu gets from birds/pigs to humans.  It seems like a big disconnect that EVERY new flu first incubated in a bird or pig then through contact at the slaughter got transferred to people.  I mean, it just sounds far-fetched that that’s what happens EVERY TIME, every year.  Every flu virus comes from a rural location, specifically a farm, and then gets into humans?  I mean, come on.  Every single new virus?  No way, I don’t buy it.  It might be one vector, but there have gotta be a hundred other ways too that we just aren’t seeing.

    1.  um… no.
      Not every flu. A species hopping virus is a really rare mutation which is what makes it dangerous (since humans haven’t had resistances built up for it yet) but does happen often enough to be a problem due to the sheer amount of human/animal contact in farms/slaughter houses.
      The overwhelming majority of new flu strains are mutations of existing ones from humans. Each year there’s a new mutant strain forms that dominates and spreads. These are easier to resist since people have developed some immunity to their previous versions.

      Cross continental viruses are another dangerous one, like n1h1 people in different regions have little defense to it since they have not had an infection of a similar strain in the past.

      1. OK, good.  Thanks for explaining.  So, the viruses are primarily already in people, kind of stirring around the globe moving through populations, and then at the onset of the flu season, a big one dominates and washes over the planet?

        1. In a given area, one will tend to dominate. However, it’s not generally the same flu planet-wide. Influenza has to travel, and generally the flu most people in the U.S. get is the flu that was big in, say, China a year or two prior. Most of the effort that goes into preparing a vaccine is based around trying to predict which strand or strands that we see elsewhere in the world will be big here next year, so we have time to ramp up the vaccine supply for that year.

        2. It gets complicated. The scarry ones are flu viruses that spread to places where the population has little resistance and it can be deadly for older or young people, and with fewer people taking flu vaccines the spread gets worse.

          Suffice it to say, immunologists have their hands full.

    1. In Southern California, where we’re more likely to leave things open in the winter, we still have the same flu season.

    2. And in Australia, where in many public places (malls and schools, for instance) there are no doors or windows to close/open. That is, these places which we think of as buildings are really just open shells. Trufax. For this Canadian, living in Australia really messed with my mind.

  2. Well I did some work in Africa where meningitis is seasonally endemic.  The current thinking is that humidity is the primary culprit.  In dry air our mucus membranes in out nose and throat dry out, leaving the epithelial tissue without a protective layer of goo.  Viruses that would normally get caught up in the mucus and excreted, have more direct access to the epithelial cells and thus are more easily transmitted. 

    Similar conditions on airplanes with cool dry air at cruising altitude are thought to contribute to increased transmission during airline travel.  So stay hydrated on an airplane may help keep the flu away.

    The protective immunity of snot is a very active area of research.  Who knew?

    1. Over the last 20 years, I’ve done a lot of flying for work, both getting to and from places, and doing work flying on planes. I used to get sick after any flight over 7 hours (the majority of my flights), until I discovered Airborne. They had shitty clinical trials, but my own theory is that the product does have some vitamin benefit, but more importantly, it encourages people to stay hydrated. So yeah, anecdata.Drink more fluids (minus the alcohol).

  3. I live in Colorado where things are pretty dry. I had air conditioning put in last spring and had a humidifier installed in line with the furnace at the same time. It was something like $300 and is worth every penny just to wake up in winter without feeling like all the moisture in your body has been sucked out through your lips.

    1. Also live in Colorado.   We have a Skuttle humidifier that operates with our furnace.  I’m fine when I’m home, but when we went to Santa Fe last year, we got so dried out the mucous membranes in our noses cracked and bled.  I swore then I’d never go anywhere again in winter in the Rocky Mtns. without taking our portable humidifier with us (if possible).

  4. I suspect that the colder temperatures and reduced humidity may play a factor in the annual flu season.  Yet I agree with awjt, that the flu outbreaks largely have to do with human behavior.

    Lately, I think they specifically have a great deal to do with human behavior running pharmaceutical companies.

    Unlike pretty much every other vaccine known to man, the nasal inhaler version of the flu vaccine is basically a selection of three live flu vaccines that you purposely infect yourself with, simultaneously.  Then you have the flu, or flus.  Then you spread the flu to your loved ones, and co-workers, by you know, breathing.  And everyone else who opens the doorknob you just opened after sneezing into your hand.

    The inhaler vaccine is supposed to contain a weakened version of the viruses; however, although it is thimerosol/mercury-free (one of the most horrifically toxic substances known to man), the flu viruses in the inhaler version are — very frequently — very much alive.  

    So, seemingly like clockwork, everyone gets the flu(s) as soon as the inhaler “vaccine” is released.  Quelle surprise!

    Scientists, medical geeks, and angry nurses take note:  That said, most vaccinations are a wondrous gift to mankind, a triumph of science, the salvation of us all, etc., etc.  So, consider getting the mercury-laden flu vaccine inoculation.  
    But, in my considered opinion, and that of many other medical professionals I have interviewed, the inhaler flu vaccine is, in short, a bane upon modern society.

    I would like to attribute the vaccine’s failings to malice, because it would make an epic backdrop for a James Bond villain, especially as retribution for pointing out the whole mercury problem.  But I suppose it’s really just a combination of foolish ineptitude, wishful thinking, and greed.  Left to rot/multiply in a vat for a few weeks/months/years.

    So, rinse your damn sinuses with some salt water (.5 t salt to 1 C warm water), and/or a little hydrogen peroxide, and/or a little rubbing alcohol.  Or better yet, also gently rub the inside of your sinuses with a cotton swab dipped in the same solution.  Infections don’t like cleanliness.  

    Your loved ones and co-workers do.  (Angry nurses of the world, please feel free to flame away.)

    1. rub the inside of your sinuses with a cotton swab

      You rather clearly have no idea what a sinus is.  They’re not directly accessible.  Even the idea of rinsing them is incorrect.  You can rinse your nasal passages and the stimulation of the cilia will provoke your sinuses to discharge goo; you don’t actually rinse the sinuses.

          1. I’ve rinsed my nasal passages almost daily for six months now, and I’ve never been happier. I can breathe and I sleep much, much better than I ever did. +1 for nasal rinsing!

    2. ANGRY NURSE HERE! Prepare for flaming!

      Actually I’m not particularly angry, but the Live Attenuated Influenza Vaccine is so attenuated that it can’t cause full flu symptoms in an individual who’s not immunocompromised. We don’t recommend it for people who live with someone who has, say, AIDS or leukemia or is having a bone marrow transplant. But if a person with a fairly normal immune system comes into contact with it, it’s not a problem. It might give you a slight case of the sniffles, but even that is incredibly unlikely because you wouldn’t be getting the same dose as someone getting the vaccine up their nose. And attenuated viruses can’t come back to health or recuperate the way other organisms might. Also, flu season has been in the winter for a loooong time and LAIV is fairly new. It’s also not nearly as commonly used, in my experience, as a flu shot. But man is it a godsend for school-aged kids who twist themselves into traumatized little pretzels over shots. Sniff, sniff, done. 

      What DOES make me angry is your sinus recommendations. DO NOT PUT RUBBING ALCOHOL IN YOUR SINUSES. Don’t put hydrogen peroxide in your sinuses. Don’t put a Q-tip in your sinuses. It is very likely that all of this would be ridiculously painful. If you want to irrigate your nasal passages, use filtered water and salt, you can make your own but even better is premade buffered sinus packets. 

      Angry nurse out!

    3. Also, thimerosal isn’t one of the most toxic substances known to man. Hell, even straight-up mercury isn’t one of the most toxic substances known to man. People used to sling that stuff around like candy and only end up as mad as a hatter. It’s not like botulism toxin or something. (Which we sling around like candy.)

  5. There is good reason to think it has to do with vitamin D levels, the season peaks with the solstice, not with temperature low, you get your D from sun exposure, and also, experiments with D supplementation do seem to show a useful effect (note, you probably want to be taking on the order of 5000iu) daily.

    1. it’s probably part of the mix of reasons, such as a disruption of regular sleep schedules, compromised immune system and of course a lot of people spending time in crowded stores and buses.

      Vitamin D may help your immune system a bit, but keeping yourself from being exposed to the virus by staying out of crowds and washing your hands and of course vaccination is the best way to keep yourself from getting sick.

  6. Webstu — Since the lead moderator here is a medical geek and angry-ish nurse, your comment may not survive to provide context for this response. In that case, I’d recommend this article at DailyBeast, where your remarks will most likely receive a warm reception.

    Yes, the LAIV — “flu mist” — treatment uses attenuated live viri; that’s why it’s named Live Attenuated Influenza Vaccine. The 3 basic injected vaccines — regular, high-dose, and intradermal — all use dead viri. But you don’t “get the flu” from vaccination; you get a template of what the flu virus “looks like” from which your body can generate appropriate antibodies. But if you feel you’ve been injured by a flu vaccine, by all means file a claim at the National Vaccine Injury Compensation Program.

    And since you say, But, in my considered opinion, and that of many other medical professionals I have interviewed… I think we would all greatly appreciate you sharing your medical bona fides with us.

    (Me, I’m just a regular guy…but I’m a Stu, too, and am interested in protecting the brand.)

  7. A simple explanation that always seems to be overlooked is just that virus is viable for longer in the cold than in the warm. Touch a door handle/Atm keypad etc and virus is left on it. It will remain viable much longer in cool/cold weather than hot weather as it waits to be picked up by someone else. It’s why scientists refrigerate their samples. 

    1. Thank you for justifying my water-wasting, ridiculously long hot showers in the winter. Also, yes, viruses can lost longer at colder temperatures. 

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