How to transmit influenza to your friends and enemies

The Pediatric Insider

© 2013 Roy Benaroch, MD

Influenza has hit, and hit hard. This year is shaping up to be one of the worst years in memory. Flu is now widespread in almost every state, and we may not yet have hit the peak.

You know it’s gotten bad when CNN routinely shows video of people walking around in surgical masks. Is it likely that wearing a mask will really help?

Flu is a specific virus—it’s not just a bad cold. Every winter there’s a surge in cases, though some winters are worse than others. The virus is transmitted in blobs of mucus expelled by people. If you’ve got the flu, you started spreading the germ one day before you got sick, and you’ll probably keep shedding virus around for about 5 days after the fever starts.

The mucus that contains the flu virus can fly out of your nose or mouth, and can infect anyone who gets that mucus in their eyes, nose, or mouth. The coughed particles don’t travel far. To transmit flu via the air, your victim has to be standing within about three feet. Anyone further than three feet away probably won’t catch flu, even if they’re coughed or sneezed on.

So airborne spread is possible, but only within about three feet. More commonly, flu is spread through the contamination of surfaces. Here’s how it works:

1.     Johnny’s got the flu.
2.     He sneezes on his hands.
3.     Johnny touches a doorknob.
4.     His sister Sarah touches the same doorknob.
5.     Sarah rubs her eye with the same hand that has Johnny’s flu germs from the doorknob.
6.     Boom. Sarah’s got the flu.

There’s a lot of steps that have to take place, and at every step there are things to do to prevent transmission:

1. Johnny’s got the flu. Preventing Johnny from getting the flu is an important step in preventing transmission! The fewer flu victims, the fewer flu transmission to the rest of us. Prevent the spread of the flu doesn’t just help your own family—it helps all of us!
2.   He sneezes on his hands. “Mucus hygiene” means teaching your children (and yourself) NOT to sneeze and cough into your own hands. If your hands have infectious germs on them, you’re close to spreading them around. Instead, cough into the crook of your elbow. Washing and sanitizing hands is also crucial for preventing transmission.

3.     Johnny touches a doorknob. It may not be practical not to touch anything when you have to flu—but keeping flu victims out of the public, and in their own bedrooms, will at least keep most of their germs where other people won’t touch them.

4.     His sister Sarah touches the same doorknob. Sarah’s not sick—yet. She ought to not be hanging around Johnny’s stuff. Stay away from people with flu!

5.     Sarah rubs her eye with the same hand that has Johnny’s flu germs from the doorknob. This step is very important. Flu virus on your hands does not make you sick. You can still spread it around, but you won’t yourself get sick until the virus touches a part of your body it can invade: your eyes, your mouth, or your nose. If you can develop a lifelong habit of NOT rubbing your eyes, NOT picking ot rubbing your nose, and NOT sticking your fingers in your mouth you will NOT get sick as often. Try it. If you do have to rub your eyes, wash your hands first, or rub your eyes with a tissue.

6.     Boom. Sarah’s got the flu. There’s one more line of defense—vaccinations! Though imperfect, flu vaccines protect you from flu, even if the virus gets into your system.


This year’s flu vaccine so far is proving very effective. About 90% of people who’ve been vaccinated 2 or more weeks prior to contact are completely immune, and won’t get sick at all. The remaining 10% are only partially protected—they may still get flu, but it will be at least milder.

And keep in mind: everyone who doesn’t get the flu – because they’re vaccinated and/or because they’re following the advice in #1-6—is one less person spreading flu. Fewer get it, fewer spread it.

We’re all in this together, folks. Flu can be treated, but it’s even better to prevent it in the first place.

Earlier: Preventing and treating influenza

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7 Comments on “How to transmit influenza to your friends and enemies”

  1. oldmdgirl Says:

    How effective is this year’s vaccine in children under the age of 2yrs?


  2. Dr. Roy Says:

    I don’t think I’ve seen official data, at least not so far this year. Data like this does come out, but it often won’t appear until later in the year. What we do have is good evidence of the match, and historical data on how well the flu vaccine works in well-matched years, and the clinical experience of docs like me who are seeing these kids.

    Overall in most areas of the USA this year’s trivalent flu vaccine (both the shot and mist) are very well matched to the most common circulating strain. The overall effectiveness is probably in 70-90% range– that’s very good. Even among those vaccinated who don’t get complete protection, we’re seeing much milder illness.



  3. Tracey Says:

    A friend commented that my immunity would wain if I avoided places with high concentrations of people. This sounded ridiculous to me but since you wrote on the subject I thought I’d hit you up with the question. The whole family did get the flu shot btw.


  4. Dr. Roy Says:

    UPDATE: I was overly optimistic in estimating flu vaccine effectiveness– nationwide statistics released 1/11 show overall 62% of people who get the vaccine are completely immune. The remainder will have only partial immunity, meaning they can still get flu, though probably a milder case.

    For what it’s worth, our local experience here in Atlanta shows better effectiveness than the national data. Circulating strains vary by geography.


  5. Dr. Roy Says:

    Tracey, I don’t think it’s wise to seek crowds specifically to get flu exposures. “I’m going to get sick so I don’t get sick” doesn’t seem like the best idea.


  6. Holly Misirly Says:

    Great guidance as always, Dr. Roy. Here’s my question – after Johnny sneezes on his hand and touches his doorknob, how long will the germies live on that doorknob? I hear conflicting things about how long they can live without a nice, warm human host. An hour, a day, forever?



  7. Dr. Roy Says:

    Very good question, Holly. It depends on many factors (temperature, moisture, chemicals, porosity), but in general influenza virus remains infectious for about 2-8 hours after it’s been transferred to a surface.


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