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Flu vaccine efficacy

Find out just how useful the flu vaccine actually is at preventing the flu! Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Rishi Desai.

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  • blobby green style avatar for user Avshalom Shapira
    What about publication bias in these numbers as there is a pharma incentive to publish only he positive result data
    (6 votes)
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    • blobby green style avatar for user Jason Miller
      Furthermore, more than half of the studies investigating flu vaccine efficacy are funded by the companies that profit most from their dissemination. They should've really drawn their conclusions from a larger body of evidence such as a meta analysis. It's unscientific to use one study to back up your claims, especially in the medical field. The meta analysis performed by the Cochrane Collaboration found that the flu vaccine is much less effective than this one study found. In fact, for every 100 healthy adults vaccinated, only 1 person avoids flu symptoms. I'd disagree with these claims and say that washing hands, staying hydrated, eating right, and getting enough sleep are far more important factors than a vaccination, which the evidence shows is sadly not that effective.
      (4 votes)
  • blobby green style avatar for user toni bark
    please give reference for this study. Have not seen a study where the placebo group received saline injection. THis study is not visible on pubmed.
    (3 votes)
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  • male robot hal style avatar for user Alex McDaniel
    How effective are hand sanitizers (like hand gel) for protecting against the flu?
    (2 votes)
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  • orange juice squid orange style avatar for user Peyton Ibanez
    how do doctors know what flu virus is going to be the strain for that following year?
    (1 vote)
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    • blobby green style avatar for user emily.l.mcleod
      Researchers (not your doctor) study the way the influenza virus has changed in the past and try to predict what the characteristics of next virus strains might be. I'm sure you can imagine how difficult this job is. The new vaccine is based on this information. When someone is exposed to an influenza virus strain that is different to what the scientist have predicted and therefore vaccinated against that person gets the flu (hence the 3/100 people that are immunised getting the flu).
      (5 votes)
  • leaf green style avatar for user Greg Mosier
    Am I the only one that thought the shield concept was weak? Felt like a preschool education that's suppose to be designed for advanced learners. Also, this implies that anyone that takes the vaccine can get sick if exposed to the flu enough times that a germ finally finds a whole in the shield. I'm ignorant of the subject but my understanding is that if the vaccine works for you, it works period, no holes in a shield?
    (1 vote)
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    • piceratops ultimate style avatar for user Tardyon
      This is an issue that arises when you try to apply probability to a single event.
      What 60-70% efficacy means is that for every vaccinated 100 people that are properly exposed, 30-40 of them will still contract the flu... or become symptomatic.

      However, once one has an immunity, either through fighting off the flu unassisted by a vaccine, or by vaccine assisted immunity, then subsequent exposures to the same strain will not cause the flu. (This is incomplete, as some vaccinations need to be boosted because the immune system has an imperfect memory of a particular strain over time.)

      So, essentially if the vaccine works for you, then it works one hundred percent. So, yes... the shield analogy is not very good for an individual... but it works if you think of the shield as protecting many people at the same time.
      (3 votes)
  • blobby green style avatar for user John E. Crowley
    Will you also address this similar study out of Hong Kong where they found the same flu results but also found that the vaccinated group was much more likely to get sick with other respiratory infections. http://healthimpactnews.com/2013/study-flu-vaccine-causes-5-5-times-more-respiratory-infections-a-true-vaccinated-vs-unvaccinated-study/

    Is there evidence that injecting one dead virus can interfere with the body's immune response to other viruses?
    (2 votes)
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  • blobby green style avatar for user Beth Jochem
    Technically viruses are not alive to begin with. So I'm confused about putting a 'dead' virus in the injection. What is that all about?
    (2 votes)
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    • blobby green style avatar for user dlstone
      In this context, "dead" means the virus is damaged such that it cannot do what normal intact viruses do: enter our cells, take over the cellular machinery to create new copies of themselves, then kill the cell and spill the newly-made virus particles out of the cell to infect new cells.
      (1 vote)
  • leaf green style avatar for user tim1361
    This video ignores the healthy user effect, and the low quality of studies backing the effectiveness of the seasonal influenza vaccine.

    - Cochrane Review - Vaccines for preventing influenza in healthy adults

    - Dr Lisa Jackson's out of season influenza vaccine research

    I am not anti-vax. Both I and my family have been vaccinated for some things but not the seasonal influenza vaccine. The risk reward ratio is way against this one.

    For instance you didn't look at vitamin D3. It is as effective and has none of the bad side effects.

    (2 votes)
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  • female robot grace style avatar for user divaCassandra1
    Wouldn't wearing a physical barrier, like those facemasks I saw on the news a few years ago because of SARS, also be a good form of prevention?
    (0 votes)
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    • blobby green style avatar for user Darrell Looney
      We have to stop ignoring basic epidemiology here. Viral illnesses are spread through contact. No contact, no spread. Coughing and sneezing release droplets into the environment, permitting opportunity for contact with other individuals. The video needs to be wound back to and add 5) COVER THE MOUTH/NOSE of the sick person. Which means using a mask to stop droplets (which are MUCH larger than viruses). THIS is the single most effective mechanism for preventing spread of the cold/flu. Vaccines are second line defense AT BEST because of their variable efficacy. The 2012 vaccine was reported to be at most 40% effective in retrospect. This is all only part of the story because we only are presented a representative 3/100 people who were confirmed positive AFTER receiving the flu vaccine, but how many had symptoms? And the presence of symptoms is what people use to make decisions on whether to receive treatment. The author of the video needs to "stop towing the party line and touting how wonderfully effective the vaccine is", thereby adding fuel to the argument to have certain segments of society forced to receive a vaccine for which a waiver of liability must be signed first in order to get it.
      (1 vote)
  • duskpin ultimate style avatar for user Victoria
    How do they kill viruses without damaging the proteins for vaccines?
    (2 votes)
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Video transcript

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.