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Flu vaccine risks and benefits

Learn about some of the common and uncommon risks and benefits associated with the flu vaccine! 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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  • male robot donald style avatar for user dan
    so the immunized persons in the "herd" actually have an invisible force field around them? I assumed the virus would still enter their body, but their immune system would be ready to defeat it. I thought this would mean that the immunized persons could still potentially carry the virus to an unimmunized person. Could you please correct me.
    (3 votes)
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    • leaf green style avatar for user Taylor - Medical Student
      Herd immunity actually is referring to the likelihood of transmission of the disease. When a large percentage of a population is vaccinated or immunized against a disease the chance of encountering an individual with the disease is much lower.

      If an individual with the disease encounters, lets say five other people, and all of these individuals are vaccinated or immunized then the disease transmission is prevented. When the ability of a virus to transmit from person to person is reduced to a specific level it is considered a "Herd Immunity".

      In short, the individuals without immunizations or vaccinations are still able to get the disease but the likelihood of the disease being transmitted to them is drastically reduced. Hope this helps!
      (10 votes)
  • male robot donald style avatar for user dan
    so an immunized person cannot carry or transmit the Flu virus?
    (2 votes)
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    • aqualine ultimate style avatar for user alleigh76
      You can still give it to someone, though it's far less likely. If you touch something that has the virus on it and you shake someone's hand before the virus is killed, you can transfer the virus to them. But you won't transmit it via coughing and sneezing, like you would if you had the flu (except maybe for a brief period time after exposure, if you happen to cough or sneeze for some other reason). The virus can only live on your hands (or a surface) for so long, and it can be killed by simply washing them, so it's pretty unlikely that you'd make someone sick that way. With the live virus, if you develop a runny nose, there might be a small amount of virus in the mucus, but that's not very likely to make anyone sick, either.

      That's my understanding of it, anyway. The vaccine only causes your immune system to kill the virus when it's inside your body, so any viruses that it can't get to are unaffected. If you get exposed to the virus, there may also be a short period of time between exposure and immune response where, as I said, you might be able to transmit it if you happen to sneeze. I'm not sure how likely it is for a vaccinated person to transmit the flu, but it should theoretically be possible for those reasons.
      (2 votes)
  • blobby green style avatar for user toni bark
    if you are negating any links between vaccine and other issues, what study are you using to make your estimate regarding attributable rate? the mathematical equation for attributable rate includes a population exposed (vaccinated in this case) to a population unexposed (un vaccinated). Again, please cite your reference for these statements. cant find any like that on pub med
    (4 votes)
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  • duskpin ultimate style avatar for user Lilyanna Rose Simmons
    at he talks about the Vaccine Efficacy being 60 to 70%
    Does that mean for both types, the TIV and the LAIV?
    Could one have more Efficacy than the other one?
    (2 votes)
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  • blobby green style avatar for user Temitayo Adegbenro
    just curious can vaccines actually kill people or do more harm than good, if so how and why?
    (0 votes)
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    • aqualine ultimate style avatar for user alleigh76
      When vaccines first started being made, there were several incidences where they were contaminated, either by live (not weakened) viruses for the disease they were vaccinating against, or by some sort of bacteria or fungus. A lot of people died from these mistakes, but because of them, the companies who make the vaccines now know to make sure they're handled properly and made exactly right. Every now and then, a batch will get contaminated (a batch of steroid shots--not a vaccine, but still relevant--was contaminated with fungal meningitis last year), but it usually gets noticed and recalled pretty quickly, and the people who received it are monitored so they can get treatment quickly if they do get sick.

      Even in the early days of vaccination, when quite a few people died from mistakes, it was still a great deal smaller than the number of people who died from the actual disease. Vaccinations save tens of thousands of lives per year. As terrible as it is that people have died or suffered serious complications as a result of vaccinations, this is incredibly rare and represents barely a tiny fraction of the number of people who would die from these illnesses otherwise.
      (6 votes)
  • mr pants teal style avatar for user Tim
    I've been writing a program to demonstrate Herd Immunity on Khan Academy. I wanted to use the flu as a model, but I have been having trouble finding out things like;
    - what is the chance of infection from a single contact?
    - how is the chance influenced by the person being vaccinated?
    - how many interactions are expected, and how does this vary based on population density / lifestyle / etc?
    - are some vaccinated people rendered immune, or is the best you can hope for a high resistance? How do I model this?
    - is there a chance of natural immunity, say from previous infections or interactions?

    The program can be found here (still a work in progress, be kind!):

    I would love any help/advice on this.
    (2 votes)
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    • blobby green style avatar for user tcoope13
      Vaccines are never 100% Sometimes it is effective sometimes it is not, it depends on whether it elicits an adequate immune response from the body. There are many variables to determining whether someone will get sick when exposed. One major variable is viral load. How many viral particles did the person inhale? 10 or even 50 probably won't make someone sick. But inhaling 1000 viral particles probably would (if they haven't been vaccinated) In a vaccinated person it might take 100,000 particles instead, but that could still be enough to overwhelm the immune system. Flu viruses constantly mutate so a natural immunity is unlikely for most people. However there is always a small subset of the population with a natural immunity to almost any concievable pathogen.
      (2 votes)
  • blobby green style avatar for user Jim Riordan
    Thanks Dr. Desai! I appreciate the numbers that you included for how often the "uncommon" risks and benefits are observed. I was interested to put them in a form that made them easier to compare so that I could see where the numbers lead.

    First the benefits:
    ~200,000 hospitalizations resulting from contracting the flu as a % = 200,000/315,000,000 = .063%
    <= 49,000 deaths resulting from contracting the flu as a % = .015%

    Now the risks (ignoring GBS since it seems like an anomaly):
    1/1,000 Febrile Seizures resulting from flu vaccine as a % = .1%
    As a number, this .1% of 22,900,000 children under 5 in the U.S. in 2011 translates to 22,900 children each year getting Febrile Seizures which result from flu vaccines (my estimate is based on http://www.childstats.gov/americaschildren/tables/pop1.asp?popup=true).

    Regarding children under 5 years old from 2010-2011, the CDC reported 60 deaths (http://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html see bottom left chart)and 20,000 hospitalizations (http://www.cdc.gov/flu/protect/children.htm). This translates to a death rate of .0002% and a hospitalization rate of .087%.

    Based on this much, it seems that the "uncommon" risks and benefits are very much that: uncommon. An interesting observation is that if all children under 5 got the flu vaccine, we would expect to see 22,900 (.1% * 22,900,000) children having Febrile Seizures. This means that more children would be having seizures than are currently hospitalized by the flu. Is my math right?
    (2 votes)
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  • blobby green style avatar for user Mohamad Koudsi
    If it's dead virus then who is responsible for the runny nose?
    Is it dead virus or attenuated ?
    (1 vote)
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  • leaf green style avatar for user T. Goodman
    Should an adult that has never contracted any Flu Virus there whole life worry more about getting vaccinated then someone who gets it often?
    (2 votes)
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  • mr pants teal style avatar for user Alexandre Jose Andrade
    Where do you get your Vaccine Effectiveness stats from? On the CDC website where they track it, the effectiveness changes every year, and lately has been trending down as of last year to 23% http://www.cdc.gov/flu/professionals/vaccination/effectiveness-studies.htm.

    How can you state that the effectiveness is between 60-70% when every year a new vaccine is made for a different strain? It is too short of a period of time to make an extremely effective vaccine unless the strain does not change or manufacturers/WHO get lucky.
    (1 vote)
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Video transcript

So a lot of people are trying to decide about whether flu vaccine is for them. They want to know, what are the risks and what are the benefits of getting the flu vaccine? So I'm going to write up here the risks and benefits. We're going to go through them kind of systematically, and hopefully by the end, you'll have a nice little table you can look at to take a look at kind of both sides, side by side. So let's start with some of the common issues. What are some of the common things we know are going to be a risk with the vaccine? Well, when you walk in to get a vaccine, you kind of know, if it's an injectable vaccine, that the injection is not going to be pain-free. I mean, most injections are going to hurt a little bit. And so this, actually, for some people is not a big deal. But for others, like me, it is a big deal. You know, I always remember, people would tell me, oh, it doesn't hurt that much. And I would feel like they lied to me, because I always felt like it did hurt. And so I always got some arm soreness. And it's not pleasant. And that was one of the main reasons I often kind of dragged my feet about getting the vaccine. I thought, well, you know, do I really want to go in today and get an injection in my arm? And the one that causes arm soreness, the one that we inject, is the dead vaccine. I just want to make it very clear. And we call it TIV. That's the name of the vaccine. So if you don't like getting an injection in the arm, if you're like me, then you can also get the other vaccine. There's this other vaccine out there. And it's going to cause, potentially, a little bit of a runny nose. This is something that some people get. I've actually always opted for this one whenever it was available. It's the live vaccine. And it's not for everybody. Some people are actually not going to be able to get this one. Now, in all the years I've had it, I've actually never had a runny nose, although I know a lot of people say that they've had that. So these are the common issues, or the common risks you take when you get a vaccine, right? Now, another thing is that they often are thought to cause the flu, but they actually do not cause flu. This is a huge misconception. So I want to make it very clear. Something that is dead-- a virus that is dead-- is not going to cause flu for sure. So that one's kind of obvious. But even this weak virus, this weakened virus that's in the vaccine, is also not going to cause the flu. It causes symptoms that sometimes are unpleasant, like a runny nose, usually, but it doesn't cause the flu. So what about the other side? What are the benefits, the common benefits that we know you can get from the vaccine? What are the reasons we even take vaccine? Well, you want to stay healthy. You don't want to get flu. And that's the whole point behind this. And this is kind of how I qualify it to myself. I think, well, you know, would I even be OK with getting an injection in the arm? Probably, yeah, because I know that in terms of pain, that might hurt a little bit, but being on your back in bed for three or four days, sometimes more, because of the flu, that's awful. And that's real suffering. So I would definitely opt for getting a vaccine over getting the flu. Now, you know, we measure something called vaccine efficacy-- kind of the ability of the vaccine to prevent us from getting ill. And the vaccine efficacy of this vaccine is not perfect. That's something we have to remember, right? It's not 100%. It's actually, we think, somewhere between 60% and 70%. So if I'm going to draw a little force field, a purple force field, showing that I'm protected from the flu, I've got to actually also show a couple of little holes in my force field to say that it's not a perfect bit of protection. But it's pretty good, and that's the whole point, right? So those are the common benefits that you can expect. Now, let me draw a little bit more space up here so I can continue with this risk/benefit analysis. What are some uncommon things? What are some uncommon, more rare events that you may have heard of, people sometimes talk about, with the vaccine. And there are a couple. There are two that kind of jump to mind I'll talk about. One of them is called Guillain-Barre. Kind of a tough word to even spell. But it's basically a nerve disease that causes problems-- actually, instead of disease, let me write syndrome. It's basically going to cause problems with muscles. And so you get muscle weakness. So Guillain-Barre Syndrome-- sometimes we call this GBS, so you might see GBS-- is essentially a nerve disease. And the reason we even talk about Guillain-Barre-- you might think, well, what do nerves have to do with the flu vaccine? Well, it turned out, interestingly enough, that back in 1976-- so we've been giving flu vaccine for a long time-- back in 1976, it was observed-- and this was unbelievable how they were able to find this, but they found one extra case-- one extra case, approximately, of Guillain-Barre So one extra case of Guillain-Barre Syndrome among 100,000 individuals that were vaccinated. So they said, well, that's interesting. We didn't expect this person to have Guillain-Barre. And there seems to be an association with the vaccine. So as a result of finding this kind of risk back in 1976, we've been looking ever since. So in the last 30, 40 years we've been kind of looking every year, and people are kind of encouraged to report if they have Guillain-Barre And we have not seen a real association between the flu vaccine and Guillain-Barre ever since this year. But we still continue to look. And people still talk about Guillain-Barre and ask questions about it. So that's why I wanted to bring it up. Now, the other thing that actually, I think, people talk about maybe even more commonly than Guillain-Barre, is febrile seizures. And if you've ever seen one, these things are pretty frightening. These are basically a seizure in a young child after a fever. And I completely understand why parents would be worried if they ever see one like this. And you wouldn't want to see one in your own child, of course. But the risk of febrile seizures with flu vaccine is also quite low. So you usually see about one case among, let's say, about 1,000 vaccinated kids. So it's also pretty low. And here, the reassuring part-- the thing that is probably most helpful for parents to know-- is that if your child has a febrile seizure, they almost always get better quickly and completely. There's no kind of long-term brain damage that you get from febrile seizures-- nothing like that. So it is frightening to look at and to see. It's scary, no doubt about it. But the kids do recover really, really well. And they don't have any long-term problems. So let's jump to the other side. What are some of the uncommon benefits? And, actually, I'm saying uncommon. I should even put it in-- well, I was going to put in quotes. I guess I can do that. Because actually, some of these benefits are more common than you would think. And so we talk about hospitalizations, right? And deaths. And people think, well, you know, it's not very common to have to go to the hospital or to die from flu, right? And actually-- I wrote "die" when I meant "deaths"-- and actually, there are many, many hospitalizations and deaths happening each year in the US. These are US numbers, right? But you can kind of get a sense for these numbers and project them to your own setting, wherever you may be living. In the US, we see thousands and thousands of deaths, year after year, related to the flu. This is based on some research that's been done over the last 30 years. And hospitalizations as well. We see 200,000 per year. So these are not uncommon things, really. And what are people dying of? What is the cause of death in hospitalizations? Well, it's things like pneumonia or bronchitis. These are pretty common ailments, and they can land you in the hospital. And sadly, they can actually land you in the grave because they're so serious. And also, things like asthma. Asthma attacks can be triggered by the flu. And if you're a parent, you can really appreciate things like ear infections. And you can get sinus infections related to the flu. And more generally, bacterial infections. So a lot of bacteria like to wait for the flu to infect, and then right afterwards they kind of jump in and cause infections as well. Let me just spell this out just to clear up any confusion. So these are actually fairly serious issues, right? These are not trivial. And they're much, much more common than a lot of people think about-- all these things, right? And so when you're comparing them side by side, on the one side-- on the benefits side-- you're avoiding hospitalization and death from fairly common things. And on the other side, you have truly uncommon things-- things that happened and were noticed a long time ago, or people recover completely and fully from. So between the two sides, again, I would say that, based on this information, the benefits win out over the risks. So now let me just bring up a little bit more space. And I'm going to get into one final issue, and this is around something that is really troubling. This is around myths, things that simply are not true. And there are a lot of them, actually, around flu vaccine. There are a lot of myths. And over the years, I've noticed that there's been a shift. So a long time ago, I would always hear the same question. People would say, hey, isn't it true that the flu vaccine can cause autism? Because I heard that on the internet, or my mom forwarded me an email about that. And that is definitely and completely not true. So this is not a real thing. That does not happen. And then later, over time, I started hearing, well, maybe it's not the vaccine. Maybe it's something inside the vaccine. Maybe it's this thing called thimerosal. Or maybe something within thimerosal, because thimerosal is actually a preservative. Maybe it's this mercury within thimerosal. And maybe that causes autism. That was kind of the new thing, I would say, a few years ago. And that also has been kind of proven, and shown in studies, not to be the case. So what do people actually talk about nowadays? What's the new myth on the block? There's always a new myth on the block. And the new one is maybe, just generally speaking, too many vaccines-- and nowadays, it's funny, I don't even hear about autism so much-- they say maybe too many vaccines are just bad. And literally, that's exactly what people will say. They'll say, I don't want another vaccine, because I've just heard it's bad. And maybe more generally, they might say, bad for the immune system. So this is kind of the most common new rumor on the block, or myth on the block. And so I want to just kind of go through these-- and we'll go through these in other videos one by one and talk about why they're not true, but it's very clear, based on research, that these are not true. But now, separate from myths, what's one final argument on the benefits side? Well, it's called herd immunity. And you may have heard this term before-- you may have heard about herd immunity. Kind of hard to say a few times out loud. But herd immunity is basically the idea-- let me try to sketch it out for you-- that you have a community, right? You've got all these people. Each white circle is another person, and they're all living together in a community. And some of these people are going to be what we call vulnerable. So let's say that this is a three-month-old beautiful little baby. So a three-month-old baby. And this baby is too young to get the flu vaccine. But of course, Mom and Dad are right here. So Mom and Dad get the vaccine. And maybe Uncle Joe gets the vaccine, and Auntie Smith gets the vaccine, and Grandma, Grandpa get the vaccine. And cousins who are also around the baby get the vaccine. And so you get the idea. Basically, all the people around this baby are going to get the vaccine. And now a stranger comes to visit. This is a person from another city. They come to visit. And what everyone doesn't know is that this person's actually sick. And they come to a dinner. And they start coughing. And of course, they're spreading germs. Well, what this family has done is that they've created this nice little zone, it's called "the safe zone," between anyone that's sick and the baby. So these germs are not going to be able to kind of penetrate this barrier because too many people are vaccinated, and so these germs can't cause enough infections to get to this baby. So this baby is really protected over here. So that's kind of the goal, is you want to keep vulnerable members of our community-- including babies and the elderly and other folks-- you want to keep them safe. And the best way to keep them safe is by getting vaccinated and creating that protection for yourself.