Why do some vaccinated kids still get sick?

Editorial Board

Editorial Board

June 18th, 2015

Editorial Board

‘This is a question we come across a lot. The short answer is that no vaccine is 100% effective.’

Immunity is not like flicking a light switch; there is no simple on/off button. Sometimes an individual’s immune system just doesn’t respond to the vaccine. Or perhaps the vaccine has lost potency because it is out of date or has not been stored correctly. In the real world, these things can happen. And mild disease can occur despite successful vaccination.

But these are not reasons to skip vaccination. In fact, it makes it even more important that everyone – unless you are too young or too sick – is vaccinated.

The Robert Koch Institute offers the following example to illustrate this point:

Imagine a measles epidemic occurs in a primary school. Half of the children are immunised, the other half not. Statistically, one can expect about 97 or 98 percent of the unprotected pupils to get sick – but only two to three percent of the vaccinated pupils.

Vaccines can also help reduce the severity of disease. This means that even if you catch an infectious illness you are less likely to suffer serious complications.

‘But I heard that more vaccinated people got sick during an epidemic in my city.’

This can happen. When it does, it causes serious confusion until you look more closely.


The History of Vaccines project at the University of Philadelphia explains this neatly:

“During an outbreak, the number of vaccinated individuals who get sick will often outnumber the unvaccinated people who get sick. This, however, is not because vaccines are ineffective, but because there are so few people who avoid vaccination in the first place. Look at the numbers for a hypothetical outbreak:

You have a group of 500 people who have been exposed to an outbreak of a rare disease. Of those 500 people, 490 have been vaccinated; 10 have not. Different vaccines provide different rates of protection, but in this case, let’s assume that 98 of every 100 people who are vaccinated will successfully develop immunity against the disease.

When exposed to the outbreak, all 10 of the unvaccinated individuals get the disease. What about the 490 who were vaccinated?

Based on the assumption of 98 of every 100 people developing successful immunity (leaving two of the 100 unprotected), about 10 of the 490 vaccinated individuals will get the disease—the same as the number of unvaccinated individuals who came down with the disease.

Those numbers, however, don’t take into account the percentage of vaccinated and unvaccinated individuals who got sick. Of those who fell ill, 10 had been vaccinated and 10 had not. But the 10 who had been vaccinated are only (10 / 490) = 2% of the individuals who had been vaccinated in the population of 500. The 10 who hadn’t been vaccinated are (10 / 10) = 100% of those who weren’t vaccinated. The final results of the outbreak, therefore, look like this:

  • Population size: 500
  • Vaccinated individuals: 490
  • Unvaccinated individuals: 10
  • Percentage of vaccinated individuals who fell ill: 2%
  • Percentage of unvaccinated individuals who fell ill: 100%”

So the risk of contracting the disease is many times higher in the unvaccinated group.


  1. Kiwi


    April 10th, 2019

    Personally I think it has to do with the person, and not that if you get sick with something and overcome it your immune system gets better. Some people are more sickly than others even if they haven’t been vaccinated yet. Anyway I respect your opinion I think it’s interesting

    • Pogi


      April 14th, 2019

      Idiot that’s not an opinion. It’s a fact. Please stop destroying humanity, anti-vaxxers. Numbers don’t lie and statistics will tell you that vaccines ‘ benefits truly do far outweigh the risks

      • Joan


        July 1st, 2020

        Actually, the information here is mythologizing. In the first world, where sanitation, clean air, water and nutritious food are readily available, flu only presents great risk to the very old and the extremely sick – and they’re not walking around much in society. The percentage of inoculated people who get the flu is many times higher than those who don’t. The effectiveness of flu vaccines is very poor and they are loaded with high amounts of deadly toxins banned by the EPA. The information above is merely theory without application in 1st world countries.

        • Gary Finnegan

          Gary Finnegan

          July 9th, 2020

          Sanitation and clean water are essential to public health. That is not in dispute. However, viruses still circulate in developed countries – measles, flu, SARS-CoV-2…
          Your claim about vaccines, which are tested and approved by regulators, containing ‘banned toxins’ is patently false. They simply would not be available in the EU, let alone recommended, if this were the case. Please consult your doctor about the best ways to stay healthy.

      • Jason A Ross

        Jason A Ross

        March 14th, 2021

        Real intelligent

  2. John


    June 10th, 2019

    We are to assume that 100 percent of the unvaccinated fell ill, don’t think so, calling someone names to their face means more than typing it out you brave person you.

    • Gary Finnegan

      Gary Finnegan

      June 14th, 2019

      No, thankfully that’s not what happens.

      Separately, according to our Guiding Principles, comments should be based on facts and should not contain personal insults.

      Please keep this conversation rational and respectful.

    • Suzy


      June 19th, 2019

      If someone doesn’t want to vaccinate their kids that is their right! Just because you are not vaccinated doesn’t mean you will definitely get sick since unvaccinated children are usually healthier. Everyone needs to stop picking on antivaxxers since if your kid is vaccinated they only have a 2% chance of getting sick!

      • Jennifer


        December 30th, 2019

        If someone doesn’t want to vaccinate based on personal preference and not medical necessity that is fine. However those unvaccinated children should not be allowed to be in the public school systems or daycares or go to a normal drs office. They pose a great risk to immune compromised people who are medically unable to get vaccinated. Herd immunity is a good thing and children and parents should have a reasonable expectation of safety for their children in school. Personal exemptions should not be acceptable for publicly funded schools .

        • James Nichols

          James Nichols

          February 14th, 2020

          An outbreak of measles occurred in a high school with a documented vaccination level of 98 per cent. Nineteen (70 per cent) of the cases were students who had histories of measles vaccination at 12 months of age or older and are therefore considered vaccine failures.

          • Gary Finnegan

            Gary Finnegan

            February 17th, 2020

            Would you have a reference for that data?

        • Parry


          June 9th, 2020

          Well that’s a very scary mindset. I’m no anti-vaxxer but to deny the right of public education because you didn’t get vaccinated is not freedom. To make vaccinations mandatory is dictatorship. Whether they are safe or not it doesn’t matter and should be the choice of the individual/guardian. If you’re vaccinated you shouldn’t worry.. if you have a weak immune system in general, maybe you shouldn’t be attending public school in the first place.

          • Emily


            June 10th, 2020

            “Parry” If i can make a mature argument here sir , that’s really not fair to say that people who are born with weak immune systems shouldn’t go to school and lead a normal life. They need it just as much so they can learn to cope with it as an adult, after all immunocompromised or not there’s no government in the world that actually takes care of their sick and disabled with enough means to live. So they’re going to have to get up everyday as an adult to go to work to live. Those people are not at fault for being born with something that compromises their immune system. However, selfish parents who could have perfectly healthy children if they simply chose to innoculate against illnesses that were eradicted until their foolishness came around – should somehow have right to send their kids to school and potentially put someone else’s child – who has as much right as any to a proper, normal education – in danger of falling ill to something that is one hundred times more severe to them , than any other healthy child? The parents had a choice. They’re the ones robbing their children of an education. They made a choice to be selfish and leave their child at risk of falling ill to an easily preventable disease, Quite frankly, not everything is just about you and your little bubble and the peoplein your near vicinity. If the events of the past few weeks haven’t proved to people that what our world needs most is unity , community and to take care of one another , be mindful of our choices and open our eyes to others struggles and needs , that we’re better as an educated unified human race. Then I pity them. I would also like to clarify I am not comparing racism to anti-vaxx idealogy. I shouldn’t even have to say that , and i shouldn’t even have to clarify which is the far bigger problem. However, sometimes words can come across in a way not intended. My only intention was to point out that we are much better as people when we unite and take care of one another. We can make change happen in great numbers. We can open other peoples eyes. We can help educate people and understand one another. Anti-vaxxers might not be bad people but they are uneducated , and they probably aren’t to blame for that. The problem is many of them will dispute what their children are taught , and refused to listen with any reason or sensibility. Even when faced with a multitude of scientific data that says they should. That’s not community, that’s not unity they put others at risk with their closed-minded near cult-like mindset. It’s not what the world needs. It is a shame for their children, they’re victims of false information. However many of them are so hard-set on their beliefs they choose to homesechool.

          • John


            July 1st, 2020

            I was wondering why people who are vaccinated care if they are said to be safe because of the vaccine so what’s the problem.

          • Ryan


            January 21st, 2021


            “To make vaccinations mandatory is dictatorship.” No one is making them mandatory. It’s a requirement if you wish to access a specific service of the govt. If you don’t want to, you don’t have to, but that means your child will have to attend education either through home schooling or private sources. You have that choice.

            In a dictatorship you would not have the option to not vaccinate. America gives you the right to not, but also restricts access to certain services if you do not. Just like you have a right to travel, but that doesn’t mean you get to drive a car on public roads if you can’t pass the licensing requirements.

            People like you seem to think that “freedom” means you can do whatever you want, whenver you want, no matter what. That’s not how this country has ever worked.

        • amy j plauger

          amy j plauger

          December 22nd, 2020

          so should the vaccinated children be allowed to attend school or the same dr.as others when some years their vaccinations are only half as effective leaving them at risk to not only catch but spread the diseases as well?

        • Jason A Ross

          Jason A Ross

          March 14th, 2021

          Then maybe they shouldn’t have to pay taxes for public funded schools since they can’t go because of personal exempt. Communist

      • Davo


        June 21st, 2020

        Once in a while I’ll bring up the point that in the past, say in Venice, Italy during the renaissance, the cities were crowded and completely filthy, in terms of what we’d consider ‘filthy’ today. There were plenty of people existing in that mess of uncleanliness, yet, they survived mostly. They may not have lived a very long life because of basic hygiene, but, you can certainly imagine the germs and diseases present there. Modern humans would NEVER stand a chance in those environments with our depleted immune system. They didn’t have the wonderful pharma ‘gods’ to shoot them up, of course, and that didn’t happen until not too long ago–compared to human history. They system is massive, powerful and has billions of dollars to spend on their products, how it is labeled and presented, and, of course has access to all the powerful media outlets, and most detractors have none. I could find very little dissenting info on vaccines when searching and I know there’s plenty of people with great, well-documented research explaining many nefarious activities and practices of pharma, to name one. Corporations, let’s not forget, ONLY exist for profit; they are not kind, humble, benevolent entities; they use money and power for whatever purpose serves them and it’s up to you to investigate and figure it out. They control the gov and it’s obvious is anyone is paying attention. No punishment if your product harms, kills, injures or just doesn’t work as promoted. Yet, if I leave my rake out on my walkway and a stranger trips and gets hurt, I can be made to pay their bills via the law.

        • Gary Finnegan

          Gary Finnegan

          June 22nd, 2020

          Life expectancy by world region from 1770 to 2018
          If we go back to the 14th century, 50 million people (more than half of Europe’s population at the time) were killed by the Black Death. Better hygiene/sanitation, improved living conditions and advances in healthcare have doubled our life expectancy.

          • amy j plauger

            amy j plauger

            December 22nd, 2020

            I have also researched this over and over our total death tolls from all diseases were going down prior to the vaccination program and with all we have done the united states death rate is suspiciously worse than what we call some third world countries so if we are right about science of vaccines why are more dying here than where they don’t overvaccinate children under 2.I hate the term antivaxxer it’s a word used to much there is a difference between not at all and delaying these shots unroll school age which I have done to my younger children and are completely vaccinated to school standards but due to delaying it unroll school age they received maybe 20 instead of the recommended 72. it’s too much and the proof is there for both .we were taught moderation in all things.

        • Mara Diane Grose

          Mara Diane Grose

          July 24th, 2020

          Yes pharmaceutical corps make billions, however only if what they sell WORKS, so being angry at them doesnt matter.
          Italy during the renaissance, however filthy, did not experience the scale of travel and return which would introduce contagious diseases in the way they are spread today.
          Overpopulation and our constant exchange of peoples from all over the world in every major city results in regular exposure to preventable, serious diseases. While we in the US have the right to refuse vaccines, the current movement against them is beyond being responsible citizens who would now believe their choice is the only one.

        • Jules


          July 10th, 2021

          I think your comment is spot on. The pharmas seem to be exempt from any harm, yet us as individuals, are not.

    • ur pp small

      ur pp small

      November 26th, 2019

      ok boomer. have fun with your kids dying

  3. EyesOpen


    September 13th, 2019

    I’m 32 and I’ve had 0 vaccines. I’m never sick. Never. I compete in triathlons and am healthier and look way younger than anyone I know. Never had ear infections as a kid, never had that cough, never had the ailments most kids had.
    Do I believe in vaccines, sure.
    Will I vaccinate my kid, probably yes.
    Do I think people need to stop glorifying vaccines and thinking they are the messiah of medicines and not flawed, yes.
    No one questions vaccines, they have this over simplified view on them: introduce a disease into the body and let the immune system fight it out so it creates a memory of way to do if that same disease is introduced again.
    News flash, our immune systems are not that simple.
    Let’s scrutinize them a little bit more. Let’s do comprehensive unbiased studies on adult child vaccinated vs adult children who haven’t been. I’m talking super in depth studies because they don’t exist.
    I’m not against vaccines, I’m just tired of this polarization: either you think vaccines are murderous or you think they save the world with no consequences. How did we get this way?

    Doctors are not scientists. Keep that in mind.

    • Jessica


      October 31st, 2019

      Great answer!🙏

    • Lg


      August 29th, 2021

      Many doctors actually are scientists! Who do you think runs all the clinical trials that tests the vaccines in patients?

    • Dr. Bybel

      Dr. Bybel

      September 11th, 2021

      Hi PhDs who are the ones who RESEARCH THIS AND COME UP WITH THE SCIENCE THAT LEADS TO VACCINES ARE VERY MUCH DOCTORS. Shut up, sit down, and learn to read.



    October 2nd, 2019

    My child is 13 and has had all her vaccines and she is always sick. She now has Whooping Cough

    • Doctor Doctor

      Doctor Doctor

      December 25th, 2019

      Dear Teresa
      Getting vaccines will not make you immune from illness. They simply save your life, and lessen the effects of some illnesses. Your daughter comes in contact with sick kids everyday, so it’s understandable. Sounds like she has a weak immune system, and would benefit from fruits, vegetables, vitamins, and plenty of sunshine. She’ll out grow her problems, as she matures.

      • James Nichols

        James Nichols

        February 14th, 2020

        This is what everyone needs full stop. The issues here are immunity. Its humanities bad habits that create sick societies not diseases. Diseases are a result of wrong things in the world, everything has a cause. Disease is not normal, it is an abnormality, something that wouldn’t exist in a perfect environment and within perfectly healthy individuals. The answer then is not vaccines, but make people’s habits and the world right.

        We will all wake up one morning in a world where we are told, in order to be healthy we must take vaccines. Stupid. Simply stupid. Humanity has killed itself and is trying desperately to rectify the problem with drugs rather than correct themselves.

      • Esa


        November 3rd, 2020

        Doctor Doctor,

        If Teresa daughter has a weak immune system, what’s the point of mandating vaccination for her, how come people push vaccination never address the issue of kids who have been harmed by vaccines

    • Danish


      January 9th, 2020

      Now I am afraid of vaccination.

      I had been properly vaccinated. But I have been sick most of my life. Once or twice every year. I am currently sick due to cold, again.

      I think vaccination reduces immunity to other diseases such as cold and pneumonia. I think I won’t vaccinate and let Allah ( God) look over my kid.

      • Gary Finnegan

        Gary Finnegan

        January 10th, 2020

        There is no vaccine against the common cold. Discuss your thoughts with health professionals before making health decisions of this importance.

      • LG


        August 29th, 2021

        Ya but you haven’t caught polio or smallpox have you. Do some research and see what life was like before both of those vaccines were developed.

        Smallpox, measles and the flu killed 90% of native Americans alone.

        I am an ICU physician and I have personally seen hundreds of patients die from covid. I have yet to see 1 complication of the vaccines.

        Look what states ICU’s are out of capacity it is all the states that don’t have a high vaccination rate. We have almost 80% vaccination rates in my area of Massachusetts and we have very few covid patients in the ICU. Most are visitors from Florida.

        Maybe we should move that wall a little farther north?

  5. John


    December 25th, 2019

    “Eyes Open” won’t accept reality. People that don’t get vaccinated spread germs. He claims zero vaccinations and zero sickness. I highly doubt his claims, and his fitness. Anyone can make anonymous internet claims. I’ve had all my vaccinations, and I don’t get sick for one reason, because I retired. I don’t come in contact with people as often. Once your children are grown, they don’t come in contact with the population, as much. People spread germs. If you’re lucky enough to land a job, that doesn’t require human inter-action, you’ll be a lot healthier. You don’t have to be a scientist, to realize vaccinations are good for you. Germs and diseases kill innocent people every day.

  6. 4TimesAYear


    April 9th, 2020

    “Vaccines can also help reduce the severity of disease. This means that even if you catch an infectious illness you are less likely to suffer serious complications.”
    Reduce the severity? Less likely to suffer serious complications? Every season I got the vaccine, I got seriously ill 2-3 times and I have even ended up having to be hospitalized. That hasn’t happened since I stopped getting the vaccine. What about the deaths from the flu that happen in people who have been vaccinated? THEY DO HAPPEN.

    • Dj


      April 28th, 2020

      But they happen MORE (higher rates) to unvaccinated people… How do u not comprehend this?

    • Davo


      June 21st, 2020

      Some people believe anything their told. To deconstruct the raw data will often give you different results due to the fact that the way the info is written is easily misrepresented; mostly by the medical and pharma industry. We still have a neurotoxin that the NAZI’s used in concentration camps being dumped in our water supply for our teeth–no doubt the NAZIs cared about their victims teeth. There is no way to monitor the intake of such a neurotoxin in a water supply, and, that’s unacceptable, but, people listen to their dentist. Funny, though, dentist offices are always full…. one would think otherwise. The principle may be ‘sound’, but, in reality, there’s toxins being injected into our bodies bypassing all the protective ‘skin’ we have; which is there to keep out these toxins, in a manner of speaking. If it’s highly profitable, it’s not a humanitarian effort to save everyone. It’s nonsense. The history of the AMA is corrupts as any abuser of power over the years.

      A massive illusion exists in which the supposed ‘experts’ are always looking out for your best interest and that is RARELY the case, when they are called ‘experts’. In any court of law, besides lawyers being in conflict over the defendant, the ‘experts’ on each side also disagree. How is that? Experts in the same fields disagreeing? And, they are still considered ‘experts’? Wow… that’s okay, it only matters who wins on the day and if it is part of the ‘system’, then it’s acceptable. When it’s not, we’ll seek to destroy you and your opinions.

      Indeed, vaccinated people do get sick, and many unvaccinated people don’t. It’s not black or white, up or down, left or right, me or you like they try to paint everything out to be; it simply isn’t.

      • Lg


        August 29th, 2021

        It is black and white. Covid vaccines significantly reduce your risk of death. When over 9 out of 10 people who are dying are unvaccinated and more people are vaccinated than not what does that tell you.

        Fact: the vaccines work!

        I am an ICU doc the people who are going home are vaccinated and the ones going to the morgue are not!

  7. Chris


    August 12th, 2020

    The Anti Vaxxers who look for every reason for a vaccine not to work are actually just telling the pro vaxxers what we already know. 100% effective -No. Side effects-Maybe. Guaranteed to work-No. Can it be developed as fast as the illnesses arrive- not close. If i get vaccinated am i immune. Definitely not. If there was a vaccine for a fatal disease and i had a choice?. Lock and load doc. Jab the shit out of me. Just check the stats. They are not made up. They tell the story. This stuff works … to a point. The point where community transmission is slowed dramatically. Doctor – no. Nothing medical actually. But i can count.

    • Jiles


      September 13th, 2020

      I think the key phrase is if “I had a choice” and in those circumstances I agree entirely.
      Anyone who wishes to be vaccinated should have that choice, but making vaccination mandatory, which is a position towards which we seem to be drifting as regards the current virus outbreak, seems to dystopian to me, particularly given the breakneck speed at which candidate vaccines are being studied and the very much shortened safety and efficacy trials that are possible in such a short time.
      Vaccines clearly can be effective, but they are never without some side effects for some percentage of those who receive the vaccine; sometimes the side effects are severe.
      What does one say to those who do have side effects?
      “Sorry we made you have the vaccine but that’s just too bad. Anyway, it was for the greater good and by the way, you have no recourse in law because the companies that produce the vaccine have been granted indemnity”.
      I find it hard to argue in favour of mandatory vaccination as long as this risk exists, be it ever so small.
      So, freedom choice must the answer.

      • Mary Thompson

        Mary Thompson

        February 26th, 2021

        Hear, hear!

    • Lg


      August 29th, 2021

      He got A’s in Math.

      It’s the people who buy lottery tickets, play slot machines, carry credit card debt that don’t understand math.

      If anyone watch’s poker, the reason professional players are so good is they know the math of the game. It’s not reading people it’s 90% math and the rest is recognizing tendencies.

      Sadly some people need to see it up front before they become believers. So sad when patients who are dying from Covid ask for the vaccine when it’s too late!

  8. Jennifer


    September 14th, 2021

    I am 56 yo. I received measel mump rubella vaccine and got all three viruses hard AND chicken pox… So what are my chances with covid vaccine

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