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 Or perhaps the vaccine has lost potency because it is out of date or has not been stored correctly.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. Navin Palan from Gandhidham

    Navin Palan from Gandhidham

    July 6th, 2015

    Good information, I like to request if this message /communication in hindi more people of the our country (India ) are more beneficial.

  2. andy


    February 20th, 2016

    Your analogy of the drunken driver is ridiculous ..if it were a proper analogy it would read that ..people who dont get into cars are unlikely to be killed in a motor vehicle accident regardless of wether they are sober or not or vaccinated against car crashes…meaning you are unlikely to die or get sick from vaccines if you dont have them. you may however contract a disease but then again you may not..surely it is better to have immunity in a more narural way rather than a one size fits all injection containing harmful preservatives that are known to damage a definite percentage of the people….IMO the science behind vaccines make sense..however the corruption of the scientific bodies releasing these some times mandatory vaccines is unheralded in any other field except for maybe armaments……..all big business should be held accountable regardless of wether vaccines are a good or bad thing…..

      • Sandra


        March 31st, 2018

        Everyone I know who has had the measles has a much stronger immune system than their vaccinated peers. Including me. I decided not to vaccinate my children and neither of them have any allergies, been on antibiotics or any other medications and they are now both healthy adults. Their peers who were vaccinated all suffer from seasonal or other allergies, illnesses like mental illness that they take medications for. Coincidence? I’d also like to mention, we have travelled extensively all over the world with our children and never had any problems anywhere. I now know and feel confident that I made the right decision NOT to vaccinate my children 20 years ago

        • Joey


          July 3rd, 2018

          Vaccines don’t cause mental health issues; those are either inherited or are from a person’s environment. Commentary like this comes from pure ignorance. You fail to realize that your unvaccinated family benefits from herd immunity. I would like to see you take your beliefs and try to sell them to a family who’ve had to bury children who weren’t able to be vaccinated due to lack of availability and resources.

          • Jamela


            February 5th, 2019

            I’m not disagreeing but I genuinely want to know.. what would you say to the parents whose children were perfectly fine before they were vaccinated?

          • M. Kerr

            M. Kerr

            March 17th, 2019

            “Mental illnesses” are not inherited – they are *learned* behaviors they got from whoever raised them. They can be stopped when a person recognizes where they learned the behavior, what how to recognize and deal with the issue.

          • Gary Finnegan

            Gary Finnegan

            March 19th, 2019

            Many of your comments on this site ignore scientific evidence, including this one. It is not correct to say that all mental illnesses are learned. Several have a genetic component.

        • M Cottingham

          M Cottingham

          September 12th, 2018

          Amen…Thank you!! Same with my 3 girls. They are not adults, but 2 teens & 1 younger. They are very healthy girls…never antibiotics, allergies etc. Yhey hate meds.

        • Danielle


          October 24th, 2018

          Please understand that anecdotal evidence is not scientific fact. Just because your kids don’t have allergies, doesn’t mean anything.

          It’s like, if 100 parents put their kids into the car without buckling the seat belts, and therefore 99 of those kids die in accidents, you’re the 1 parents with kids who managed to survive, going around telling everyone, “SEE?!?! WE DON’T NEED SEAT BELTS!”

          You’re participating in survivorship bias. You think there are no negative consequences for your actions because you were one of the lucky ones who didn’t have to face those consequences. But many other parents did. But their children aren’t alive to say that vaccines would have saved their lives.

          • M. Kerr

            M. Kerr

            March 17th, 2019

            One’s personal experience is not the same as “anecdotal”. Personal experience is first hand eyewitness testimony. Anecdotal evidence would be hearsay. If personal experience was “anecdotal”, the FDA would not want people calling in to report negative effects of vaccinations or other drugs – but they do indeed have a toll-free hotline to report these things.

        • Mya


          December 11th, 2018

          Hey I would really like to know what antibiotics you gave your kids I don’t wanna vaccinate my son

        • Paul


          January 18th, 2019

          Yes, Sandra, that’s a coincidence.

          “Their peers who were vaccinated all suffer from seasonal or other allergies, illnesses like mental illness that they take medications for”

          That’s called confirmation bias and cherry picking, Sandra. You looking at a few of their peers, and comparing them to your *TWO* children, is a wild misunderstanding of how percentages and sampling error work.

          “I’d also like to mention, we have travelled extensively all over the world with our children and never had any problems anywhere.”

          So did Columbus, and he was great at transmitting plagues to the new world. You could also be transmitting diseases to others, it’s not about you.

          “I now know and feel confident that I made the right decision NOT to vaccinate my children 20 years ago”

          With all due respect, you made a terribly ignorant decision based on confirmation bias that needlessly put not only your children, but other children at risk.

          That is not something you should feel proud of.

        • Van


          January 29th, 2019

          Congratulations! You and your children won the lottery. The fact is, there are a lot of other factors involved in mental health and allergies. As far as antibiotics, very few people should be getting antibiotics, so that is good your kids never had them. Although you have “traveled extensively”, you clearly have not been anywhere where there was measles, because if you had, your kids would almost certainly have gotten measles; it is extremely contagious. Of the reported measles cases in the U.S., one in four result in hospitalization. One in a thousand die as a result of the measles. It is true that there are complications with vaccines, but not anywhere close to one in four, and so far there have been no deaths associated with any vaccinations. Yes, you were lucky, but playing Russian roulette with our children is just irresponsible, and rarely has a positive outcome.

        • Wow


          January 31st, 2019

          Moron…”I’m confident in my pigheadedndecision that’s completely antithetical to every modern scientific tenet known to man!” I bet you use/sell Dotera, too.

        • Teresa Douthit

          Teresa Douthit

          March 19th, 2019

          While this may have been good for you, it’s not good for everyone.

        • Alanna


          March 19th, 2019

          No Sandra, That’s not science, that’s luck. You were lucky that your children did not get a deadly disease. Your logic is like saying, ” it rained today, it must be because I did a rain dance”.

    • Daniele Medley

      Daniele Medley

      May 9th, 2018

      This right here ☝️

      When I was reading what was written, the “analogy” My brain couldn’t even comprehend what I was reading.

      “This, however, is not because vaccines are ineffective, but because there are so few people who avoid vaccination in the first place.” WHAT????

      • Daniele Medley

        Daniele Medley

        May 9th, 2018

        In reply to Andy’s comment

      • Paul


        January 18th, 2019

        ““This, however, is not because vaccines are ineffective, but because there are so few people who avoid vaccination in the first place.” WHAT????”

        …Daniele, that’s pretty straightforward.

        If 1/10 people who don’t punch sharks get bitten, and 10/10 people who punch sharks get bitten, you’d still expect a lot more people who don’t punch sharks to get bitten

        Almost no one punches sharks in the first place.

      • M. Kerr

        M. Kerr

        March 17th, 2019

        I noticed that, too. Makes absolutely no sense whatsoever.

  3. The V-Dawg

    The V-Dawg

    July 10th, 2016

    Great comment Andy, it’s cool to see people can still think. I agree that the car crash analogy is ridiculous. You’ve made an observance you haven’t presented a case for a universally applicable rule. I wouldn’t apply that “logic” for much of anything but I would choose to not vaccinate based on the independent research I’ve done.

    • Roger


      April 29th, 2017

      Sounds interesting, can you help me understand your reasons for the conclusion you came to? Thanks for the help

    • Eric Ofoe

      Eric Ofoe

      July 7th, 2018

      I’ve tested hapetitis B negative in the year 2016 and 2017 and have the vaccine but recently I tested positive.Is it possible?If possible how come and why do we vaccinate?

    • Paul


      January 18th, 2019

      …the car crash analogy is apt, and you’re employing confirmation bias.

      “I would choose to not vaccinate based on the independent research I’ve done.”

      That is terribly ignorant and selfish. Please be more intelligent and compassionate.

  4. a person

    a person

    August 6th, 2016

    When someone types the word “vaxxer” I stop listening. The use of such informal, targeted language is consistent with the rules of propaganda. Buzz words and repetition designed to cause the reader to tune out and believe this article is the truth since they’ve seen similar messages elsewhere.

    • Anonymous


      September 26th, 2016

      You can cover your ears and sing all you want, but the truth still exists. Maybe its time to but on your big boy pants and face the truth

  5. michael


    August 22nd, 2017

    Is this math for grade 2 drop outs?

  6. Gemma


    March 22nd, 2018

    It’s so intresting that all of the above claims are made of assumption as there has never actually been a study done on vaccinated vs unvaccinated so how could any one know. You shouldn’t spread false media, just like the theory the earth used to be flat… look how wrong we got That!

  7. Joey


    July 3rd, 2018

    See, here’s the thing. We used to live in a world where vaccines didn’t exist and thousands of people died. Look up Smallpox and the number of people that died from it. Check out third world countries that don’t have access to vaccines and the devestation that preventable disease cause there.

    • Anonymous


      March 1st, 2019

      There are more factors that are at play here. We have changed sanitation, nutrition, etc. People in third world countries don’t have access to those things and still suffer. Even a paper cut can cause death by infection with no proper way to clean it or care for it. We also used to wear bird masks and beat and bleed people to stop the plague, and it eventually disappeared, do you think that was because of our “medical” intervention?

    • M. Kerr

      M. Kerr

      March 17th, 2019

      Numbers of deaths dropped in developed countries due to better nutrition and better ways to treat sick people – it’s also the difference between flu epidemics before vs. now. The flu vaccine is so “iffy”, it cannot be credited with saving anyone’s life, particularly when you have some people who actually experience the illness a number of times each season after having had the vaccine.

  8. Donnie Noah

    Donnie Noah

    November 10th, 2018

    Your assumptions are just not true. In my sons school all of the kids who got measles WERE VACCINATED, my son who was not vaccinated was asked to stay home- he didn’t get measles. Your 100 percent of unvaccinated is absolutely false and you are spreading misleading information.

    • Clint


      January 15th, 2019

      Hey Donnie Noah, seriously. If what you say is true, can you please list the details. Nothing personal, just school and year of outbreak would likely be enough?

    • Paul


      January 18th, 2019


      “was asked to stay home”

      …do you not see the problem there?

      “all of the kids who got measles”

      out of how many kids that got vaccinations? Do you understand what a sampling size is?

      “Your 100 percent of unvaccinated is absolutely false and you are spreading misleading information.”

      …your kid STAYED HOME. He didn’t get the change to get the disease, OR (more importantly) pass it to anyone else.

    • Van Reese

      Van Reese

      January 29th, 2019

      To say 100 percent of unvaccinated people will get the disease is far from misleading because if you are exposed you will almost certainly get the disease. Your son was not there to get exposed. All the kids who got measles who were vaccinated were apparently part of the 2%. Did they get the two vaccine series? What about the kids who did not get the measles? How many of them were not vaccinated? Who brought the measles to the school to begin with? You make it sound like all the other kids who were vaccinated got sick; I don’t think that was the case. Measles is one of the most contagious diseases there is. It takes only one virus to get sick, and carriers can spread the disease before they show any symptoms.

    • Tabby


      February 8th, 2019

      You know WHY they asked your kid to stay home right?! Cause he was 100% likely to contract it. Where only a fraction of vaccinated kids are likely too and at that they will have had a mild form of it, even though 40% of all non-vaccinated measles cases turn complicated and of that 40%, 20-30% get brain damage and/or die. So I’d be thanking the school and doctors for catching it before your child was infected and have enough common sense to send him home till the other students who wouldnt die from it were ok again.

      For example my kids all got the chicken pox shot and alas all caught the chicken pox. But no one else at the school caught it. My kids didn’t take the vaccine as well and idk didn’t develope a 100% immunity. It happens. Regardless they got spots and that was it. No fever, not itchy, very active and not sickly at ALL. As a child me and my siblings caught the chicken pox because you know there wasn’t a vaccine my mom said I screamed and cried the whole time and so did my siblings. That was uncomplicated chicken pox too. We had fever were itchy and miserable had the blisters all of it. I dont remember I was only 1 when I caught it but I have scratch scars from it. I asked a few doctors now about the random scars I have and everyone said they were classic chicken pox scars from busting blisters from scratching. I have like 4 of them lol my kids have 0, why because they felt fine the whole time they had it. Now tell me again how vaccines dont “work”

  9. Aaron


    November 25th, 2018

    Cool “hypothetical” outbreak. If you’re so sure if your theory, why didn’t you provide a situation that actually happened?

  10. Andrea


    March 4th, 2019

    This is the issue. As much as the medical profession wants us to believe what they tell us. The fact is approximately 5 % of the vaccinated population will become infected by the viruses that they are immunized against. The percentage is the same for the unvaccinated population. The fact is you are actually taking the virus plus many other unhealthy substances into your body. The Canadian govern ment actually publishes a form that you can claim damages from vaccinations. Our bodies were masterfully created. We have the potential to heal from any virus or disease with or without the addition of natural cures or change of diet

    • Beebs


      March 16th, 2019

      And you’re planning on “naturally” recovering from polio how, exactly?

    • Lucie


      April 4th, 2019

      Do you have any scientifical evidence to support your claim, that 5% of both vaccinated and unvaccinated people will catch the disease?

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