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 Or perhaps the vaccine has lost potency because it is out of date or has not been stored correctly.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

        • 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.

        • Mya


          December 11th, 2018

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

    • 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

  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?

  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.

  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.

  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?