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Flu vaccine efficacy | Infectious diseases | Health & Medicine | Khan Academy

November 14, 2019


So let’s say you’re
walking down the street and you see this person,
this green, sickly person. And this person is
coughing and sneezing, and you feel really
bad for them right? Because they look awful. They just must
feel awful as well. And the thought that
goes through your mind is, how do you avoid
getting sick as well? Because of course,
you don’t want to feel this way either, right? And so you want to think
about all the things that you can do to make
sure you don’t get sick from this person. And so what are
some of those things that you might be able to do
to try to avoid getting sick? Well let’s think through it. How are you interacting
with your environment? What’s the only real way
in which you interact? Well, it’s when you
touch things, right? You usually have your feet
and your body covered up, but your hands are
always exposed, and they’re always
touching things. And then you usually
turn around and touch your mouth, your
eyes, or your face. So two real quick
things that you can do to try to
prevent getting sick are simply making sure
that you wash your hands. And that’s why you
always hear that message, wash your hands after going to
the bathroom, before you eat. And that’s the reason why. And the other key message
is, don’t touch your face. Right? You want to make sure
you avoid your mouth, your eyes, your nose. Because that’s where the
viruses get into your body. So don’t touch your face. So these are two really
good ideas, right? But what are some others? What else can you do? Well, you can try–
and this isn’t always possible– you can try to
avoid the person altogether. You could try to just
move away, right? You could say, well, let’s
make some distance over here. So you’re further
away from this person. And that’s another
possible strategy. And like I said, it
doesn’t always work. But when you can avoid someone,
that’s always a good idea. So avoid sick people. And finally– and
this one is going to be the main point
of this video– is you can actually get vaccinated. You can get a vaccine
that will actually prevent you from getting ill. So flu vaccine is something
that a lot of people have strong feelings about. And the first thing
I want to point out is, on this list of
prevention it’s probably the most important. It’s probably the
most effective way of preventing getting
sick from the flu. So certainly think about it. But if you’re going
to think about it, and you want to think
critically about doing something like this, you want to make
sure it’s a good idea, right? Do we really have any evidence
that it really does help? Or is it the opposite? Does the flu vaccine
actually make you more sick? Does It gives you the flu? So let’s talk about that. Let’s think through
how the vaccine works and what we know about it. So there’s some research that’s
been done on flu vaccine. I’m going to present you with
what we’ve learned so far. So a group out of University
of Michigan actually came along and they said, well,
let’s figure out the answer to whether
vaccine is a good idea. And let’s actually take–
let’s start over here on the left side–
let’s take an injection and fill it with salt water. So this is regular
old salt water, or something very similar to it. And it has no real
effect at all. In fact, sometimes
people call this placebo. And I’ll actually write
that over here– placebo. So that’s one side. And on the other
side, let’s actually come up with a vaccine. And this vaccine I’m
going to draw out, it looks basically the same. It’s actually also an injection. And this injection is
full of dead virus. So they literally take
live virus– remember live virus has kind
of an envelope, and it has RNA on the inside. I’m going to sketch that out. And what they do
is they actually have different
ways of killing it. They literally just
destroy this thing. And just like human beings,
you know, if you’re killed, you cannot come back to life. And a virus is the same way. Once a virus is dead,
it is dead forever. And so this dead virus is
lying here on its side, completely and
utterly dead, right? And this dead virus,
then they take it and they put it
into the vaccine. So this is what
is in the vaccine. This is our flu vaccine. Let me label it over here. Flu vaccine. So two groups of
people then, are going to get two different
types of injections. And they actually had
hundreds and hundreds of people involved
in this study, but I’m just going to show
you a representative slice. So let’s say this is
100 people over here. And that’s a grid, so each
square represents one person. And there is 100
people over here. And these people, they
don’t know which vaccine they’re going to get. They don’t know if
they’re going to get the salt water or
the flu vaccine. They’re what we call
blinded in this study. And I should also tell you that
these people are very healthy, and they are young adults. So they’re between
18 and 49 years old. They’re healthy. And the two groups are
fairly similar in terms of the number of men and women
in each group and their age breakdowns in the two sides. They’re fairly similar. So these two groups get
the salt water or the flu, and they don’t know
which is which. And they’re told over
the course of six months, over the course
of the flu season, to keep track of illnesses. And if they get flu, I’m going
to sketch them out in red. What they actually did is they
said, hey, if you get the flu, let us know and
we’ll confirm it. We’ll actually do a
lab test to make sure that it really is the
flu and that it’s not just some other illness
that you think you have. So they actually
took all these people that said they had
the flu– and I’m only going to draw them in red if
they were confirmed by PCR. That was the lab
technique they used. So these were called
PCR confirmed. So that’s laboratory-confirmed
illness with flu. So these are people with
PCR-confirmed illness. And there were, you
can count them out. Out of 100 people in the first
group, in the salt water group, we had a total of
10 individuals. So about 10% of these folks were
ill with the flu over the flu season. And on the flu
vaccine side, we also had some people
sick with the flu. So that’s actually
the first thing you should know is that the flu
vaccine does not prevent you 100% from getting the flu. But look at how many
people I shaded in. In the placebo side I said
there were 10 out of 100 people that got sick. And on the flu vaccine side
only about 3 out of 100 people got sick. And both– actually
I should put arrows on both sides– both
were PCR confirmed. So what does this mean? How do we take this and
make some sense out of it? Well, there’s a term
called “vaccine efficacy.” And what it kind
of refers to is, how good is the vaccine
at preventing you from getting sick? So this is the term
“vaccine efficacy,” and sometimes you might
even see the term “VE.” Sometimes people use “VE”
for vaccine efficacy. And the way you
calculate it, you say VE equals the proportion
of people that got sick with the salt water– so
that was 10 out of 100– minus the proportion that got
sick with the flu vaccine. So minus 3 out of 100. And you divide by the group
that did not get vaccine. And so you can take this
and you could simplify it. You could say, well,
this is basically 7 over 100 divided
by 10 over 100. And you could make it
even simpler by canceling the 100s out, and you say,
well, this is just 7/10. And to make a percent of it,
you multiply 7/10 by 100%. So if I was to describe the
VE, or the vaccine efficacy, based on this
study, I would say, well, flu has a 70%
vaccine efficacy. So you see how we
got that number. It’s fairly simple, right? Just comparing the two
groups to each other. And there have been
many studies on flu. And the CDC actually
took all this data and they said, well, in
general, the VE, or the vaccine efficacy, for the flu vaccine
is usually between 60 and 70%. That’s kind of the
number that they usually quote for this vaccine. So let’s now take
that number, 60 to 70% VE– I’m going to
write that down here, so we don’t lose track
of what that is– and let’s take that back up
here to our little example. We said that there are a few
ways to try to prevent the flu. And if I imagine
now that there’s a force field around
me– let’s say there’s a little purple
force field around me– and this force field
protects me from germs. I’m going to show germs
coming in and bouncing off my force field. Well, this would
be really accurate if I was describing
100% vaccine efficacy. Meaning if I get
the vaccine, I’m completely unable to get sick. But we know that’s not true. We know that it’s actually
closer to 60 to 70%. So for 60 to 70%,
let me show you what you can change this
picture to look like. Instead of making it
completely impenetrable, you can just draw
a few holes in it. So a few holes there, maybe be a
hole there, and maybe be a hole down here. So now you can show
a few of the germs breaking through and
getting in, right? Maybe getting in over here. But many of them actually
still bounce off. And so you’re still protected
by a lot of the germs, but some of them can
still get you sick. So probably the best way
to avoid getting sick then, is to get your
vaccine, but still make sure you wash your
hands, don’t touch your face, and avoid sick people.

28 Comments

  • Reply khanacademymedicine January 18, 2013 at 9:28 pm

    A few good suggestions here. I will put together a video on why vaccine efficacy changes from year to year and one on vaccine preservatives like Thimerosal. I also need to do one on how vaccines are made and the role of adjuvants as well.

  • Reply sdm aji January 18, 2013 at 9:55 pm

    I have a question that is not all related to the flue virus , it about hantavirus which can cause similar symptoms , can this virus react with Antibodies that is specific for this pathogen in the patients , I just thought abs are only related to bacteria ? Thanks

  • Reply khanacademymedicine January 18, 2013 at 10:01 pm

    Our immune system makes antibodies for many viruses, including hantavirus. You're right, antibodies are generally specific for particular pathogens.

  • Reply sdm aji January 19, 2013 at 1:27 am

    Thanks a lot, I got Antibodies confused with antibiotics, I know antibodies are what your body produces in response to the presence of antigens (bacterial or viral surface structures) Antibiotic are chemicals that work to destroy invading bacteria (usually by disrupting the outer cell wall and making it "leak" or by messing up the bacteria's metabolic processes. But Why antibiotics don't work on viruses?

  • Reply wjestick September 27, 2013 at 11:07 pm

    A really poor video. You started in a very logical and approachable way. You listed methods of prevention. Then totally option failure on the idea "Up regulate your immune system".
    Numerous studies have shown Vitamin D lowers Flu risk. Sunlight exposure raisers Vitamin D levels and lowers risk of flu. "The peer reviewed evidence for the benefits of sun exposure". Now that would be a neat Video.

  • Reply Liora P November 22, 2013 at 1:45 am

    Cochrane Collaboration did a METASTUDY, dude, you should read it (everybody should.  It was available for a while, then they YANKED it from their library, I have it will send, lioracc AT yahoo.com to request it .  It showed that 99 people had to get flu vax in order for ONE person to avoid influenza.  In addition, their graphs also showed that 7 out of 8 people who think they have the flu have an Influenza Like Illness, not one of the strains in the vaccine. It outlined the HARMS such as GBS and also another CC study showed that hand washing was the most effective method of self protection NOT the vax.  This video is political in nature not medicine folks.   

  • Reply Liora P November 22, 2013 at 1:54 am

    People who got the flu vaccine were more susceptible to swine flu. News report.  
    http://www.abc.net.au/news/2011-03-04/vaccines-may-have-increased-swine-flu-risk/1967508

  • Reply Fred Garvin November 22, 2013 at 2:06 am

    I used to get the flu just about every year. At age 40, my Dr recommended the flu shot. I haven't had the flu in 11 years. So it works for me. If you get the shot & still get sick, it's not for you.

  • Reply 123BDG123 November 22, 2013 at 3:40 am

    As a scientist I find this video to be disturbing.  Is this what they teach in medical school?  Does the author actually understand the scientific method and how falsification works?  This video is typical of the idiotic lunacy of the medical industrial complex and especially the drug-pimping complex that has overloaded us with useless medications.   This video IS NOT science.   I could falsify this argument very easily.  There is NO provable evidence ye to be presented by anyone that flu vaccines have any measurable benefit. 

  • Reply halbert5150 November 22, 2013 at 3:32 pm

    The problem with the FE calculation in this video is that it completely ignores the fact that for 90 of 100 people taking the vaccine or not taking it had no affect whatsoever. The true efficacy of this vaccine is 60% of 10% = 6% The way it is calculated here is a great way for the pill pushing drug companies to sell alot of 'snake oil' 

  • Reply qualmset1 November 23, 2013 at 1:44 am

    Where is the evidence to support your claim?

  • Reply Hero Miles November 23, 2013 at 7:54 pm

    I really like Salman Khan and Khan Academy, but I am disappointed in him for trying to justify why people should get vaccinated when the real truth is most people don't truly understand fully all of the ingredients in vaccines or if vaccines are truly safe or effective. This video attempts to justify vaccines when there is all kinds of information out there that suggests against vaccines. People, do your own investigation regarding this.

  • Reply Yonas Hassen November 29, 2013 at 4:40 am

    Great video, and a really good breakdown for people that don't have a medical background. However, we do need links to these studies that you reference. 

  • Reply Andy Morris November 29, 2013 at 4:58 am

    So to avoid a harmless but inconvient flue virus I should as a healthy person take this toxin laced pathogen mixture into my blood stream. Not worth it even if the study is accurate. Double not worth it if you have a compromised immune system. People get flues for a reason and has more to do with the immune system than the presence of the virus in the environment.

  • Reply amommamust November 29, 2013 at 6:06 am

    What a load of Big Pharma nonsense. I spent a career in healthcare, and refused the vaccines every year. Every year, I would wind up working extra shifts to cover all the people that got the vaccine, then got the flu. Me? I never get it. A little hydrogen peroxide in each ear once a week all winter. The best way to avoid getting sick is to avoid Pharma whores like the guy who made this video.

  • Reply EdR77203 December 12, 2013 at 7:24 pm

    If it was just dead virus and saline water I would be all for it.  You also find adjuvents, foreign proteins, formaldehyde, and a host of other things that the pharmaceutical companies don't mention. Adjuvents kick the immune system into reacting to the antigen.  What makes it stop there?  Can the adjuvents be responsible for the epidemic of asthma and other immune system illnesses?  Since it is "immoral" to compare vaxed vs unvaxed we will never know.

  • Reply stephanie popham December 21, 2013 at 6:10 pm

    Im that 3 out of 100 that got the shot and still got the flu. I really want it to go away before Christmas:(

  • Reply T Firth January 26, 2014 at 1:55 am

    A couple things here, at 3:31 it is said it is a dead virus when in fact it is only weakened or attenuated, there is a big difference, the CDC in 2001 ended live virus injection due to the evidence that it did cause the flu. Here is something to think about, in the fall of 1917 the flu vaccine was issued with the live virus. It was believed the lab used the virus from the 1897 Russian PandemicH1N1,  that pandemic killed a million people. The entire military was vaccinated by which was made mandatory. The injected consisted mainly of young men between 18 and 26, also some government workers were ordered to take the vaccine. The inoculation occurred also in other armies around the world by way of mandatory compliance. By the early 1918 the reports from Spain where there was a staging area for the allies, and the Spanish flu began claiming lives and the main age the virus attacked was not the old or the very young but it was recorded the outbreak affected an inordinate amount of young men between 18 and 26. Upon the first wave of the out break it was encouraged that even though it was late in the flu season, everyone in the general public should get the flu vaccine to help protect against the virus, all the while a hidden ban by the media alerting the public to the major outbreak within the military. It was later discovered that the military from both sides of the war were suffering the same fate, and the same ban for the same reasons. Now there were two waves to the flu pandemic in 1918, and the second wave closed hospitals and was more wide spread to all ages and in total 500 million people were affected and a near 100 million died. Two waves of the pandemic, and two waves of the same vaccines injected, the first time to those that were between 18-26 which was the targeted attack of the virus, The second wave after injecting more of the general population after the scare from the first wave and the result of the second wave showing the full population being plagued. The connections can not be dismissed, so how can anybody point to the biggest outbreak ever and not look at the correlation of the vaccines in the labs being developed?  

  • Reply Vicki Bee November 2, 2014 at 1:20 am

    If you're immunocompromised or immunosuppressed, the shot is advisable. It doesn't cost anything to get it at your doctor's officer – other than the insurance you're already paying.
    I'm a paramedic, and I'm fed up with people who claim to be health care professionals who never think outside the realm of their own bodies. Just because someone doesn't need it who's been exposed to sicknesses via their work doesn't mean everyone else is like that.

  • Reply Frank Twist January 23, 2017 at 12:48 am

    –https://www.cdc.gov/flu/professionals/vaccination/effectiveness-studies.htm
    This links from the CDC shows the flu shot has never been 70% effective as this video says.  The average effectiveness of the flu shot over the last 10 years is 41%

    This video for some reason, just mentions a Michigan study, well there are 100"s of flu shot efficacy studies and most of them are Industry funded and meaningless.  My link from the CDC shows the real efficacy.

  • Reply Frank Twist December 2, 2017 at 4:13 pm

    –https://www.cdc.gov/flu/professionals/vaccination/effectiveness-studies.htm  This shows the flu shot has been 41% effective on average over the last 13 years.
    This year, 2017/2018, the flu shot is only going to be 10% effective http://time.com/5043143/us-flu-season-2017/
         Last year it was 48%, the year before it was 42% and the year before that was 19%. Khan is using very old outdated information.
     Also very important.  Google "Serial flu shot Problem" the more flu shots you get the less effective it becomes. So you should only get a flu shot if a major pandemic comes along and then it will work much better for you.

    https://well.blogs.nytimes.com/2012/11/05/reassessing-flu-shots-as-the-season-draws-near/  This shows they have been doing flu shot effectiveness studies wrong and now realize flu shot is not nearly effective as they thought.  It is not 60 to 70% effective.

  • Reply Brandi Peck January 11, 2018 at 6:05 am

    The vaccine is toxic..

  • Reply Rob McGhie January 11, 2018 at 4:16 pm

    Too simplistic Doesn't he know what actually goes into vaccines it's certainly not just dead viruses a toxic medley of poisons like mercury etc. Science has proven the vaccine does more damage than good and not even 50 50 chance. Drs have know for years the success rate is abysmally low just like chemotherapy radiation and surgery for cancer. About the flu then it's a different strain every year and the study showed clearly that whilst flu in pregnant women was reduced in year 1 in the subsequent years it went up 250 per cent. So one can only take from that the medical establishment must be making money from all these repeat treatments.
    As the vaccinated will be much more susceptible to a flu pandemic like that of 2009 owing to their poor immune response being suppressed and less able to produce antibodies we are looking at a policy to cull millions.
    I will never take unnecessary vaccines which are an insult to my bodies natural wisdom and healing mechanisms as long as I still have the wits to be in control of what toxins I allow my body to encounter.
    They are only acceptable for those who gamble with their health and that won't eat and live healthily and look at causes not symptoms like dr's can only do. Leave the rest of us to take vit D, C..zinc.garlic and anti mucus diets etc

  • Reply Rob McGhie January 11, 2018 at 4:21 pm

    Do some simple research Look to authorities on the subject like Dr Suzanne Humphreys and subscribe to Dr John Bergman who can show you how to take back control of your health and well being. It's bleak but it's never never too late to do something to reverse your health issues however serious. Best of health all!

  • Reply ReenyNY January 13, 2018 at 2:32 am

    https://www.youtube.com/watch?v=jt9rdznYsLI

  • Reply Jeanne O'Mara January 27, 2018 at 1:20 am

    No vaccine.You don't mention all the neurotoxins in the shot and many die from the shot. They never use a real placebo w salt water.

  • Reply Bonnie Bear March 13, 2018 at 4:39 pm

    Can you please explain what is in the flu vaccine.. it would help your case if you were more truthful. And I can't find the "placebo" study from University of Michigan… it would help to leave a reference like most people do when they have nothing to hide. I see a study from 2006 from Michigan that compares two different types of nasal flu taken compared to vaccine. That's not a placebo study.. anyone? Placebo study??

  • Reply T C December 29, 2018 at 7:34 am

    Don’t get stressed and get some sun everyday. That is what I do to prevent the flu

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