i have no mouth and i must scream

First, unless there is a medical reason a child should not be vaccinated (such as an allergy to a compound in the vaccine), yes I think every child should be vaccinated!

Mutation of the pathogen can and has occurred, that is not the main reason for the vaccinated becoming sick. 

So WHY do the vaccinated get sick?

An EXCELLENT question with a variety of answers.

Some vaccines wear off with time.  That is why you are supposed to get your tetanus (and pertussis aka whooping cough!) shot every 10 years or so.  Think of it as a shirt, some shirts wear out quickly and have to be replaced over and over.  Then there is that one shirt that you’ve had since like middle school and 14 years later it’s still going strong.

Different vaccine formulation have different effectiveness.  In the mid 1990s the USA switched from using whole cell pertussis vaccine to aceullar pertussis vaccines over concerns about safety. Though the safety improvements are pretty much negligible from what I’ve seen.Those who had the whole cell vaccine are less likely to develop pertussis then those who had the acellular vaccine.

Vaccines are designed to do different things. Some vaccines work so that should the person be infected the disease is milder/survivable (Those with the aceullar pertussis vaccine for example may still get sick but their illness won’t be nearly as bad as if they were unvaccinated) or protect the child long enough to be strong enough to survive it

The Bacille de Calmette et Guérin (BCG) vaccine is a very good example of this. BCG vaccine is given to children to prevent tuberculosis. The BCG vaccine is really ineffective in adults and its effectiveness in children can be a crapshoot. HOWEVER it is very good at preventing miliary TB. And this gives children a chance to survive so that they may fight off the infection. (I’m not going to go into the pathogenesis of TB though it’s really interesting! Umm to me…)

But the BIGGEST reason is

           It’s a numbers game.

What the fuck does that even mean pvivax?

It means you have to take into account

The effectiveness of a vaccine, none of them 100%

How many people around you are vaccinated?  If everyone is vaccinated and you are one of the people where the vaccine didn’t ‘take’ your chances of getting sick are really low.  Contrariwise if a LOT of people aren’t vaccinated then your chances increase.  

An imperfect analogy: think of it as being shot at.  Someone shoots at you once and your bulletproof vest doesn’t work, you have a pretty good chance that the bullet will miss you and you’re good. But if you are shot at over and over and over, pretty soon there is good chance that you’re gonna get hit. 

Now for an example!

Herd immunity (the percentage of people that are vaccinated in order to for the disease to not spread and protect the vulnerable) is 98%.

 The MMR is about 97% effective, right? Let’s begin!

You have a school in Mississippi of 2000.  Mississippi has very strict vaccination laws. Only medical exemptions are allowed.  Therefore of the 2000 students, 1994 are vaccinated, a rate of 99.7%.

All of these students are equally exposed. If you are exposed to measles you have about 90% chance of getting measles.  It is VERY infectious.

Rounded down, since you can’t have a fraction of a person: 5 of the unvaccinated children will get measles.

54 of the vaccinated children will be sick.

OMG VACCINES SUCK THE FUCK SCIENCE!

Wait, wait, wait a moment!

Look at the numbers again!  5 of the 6 unvaccinated children developed measles, that’s a 83%.

54 of 1994 children developed measles, that’s 2.7%

But when you look at that, what do more people see?  The fact that 91% of measles cases were in the vaccinated, not that 1940 children were spared measles while only 1 non vaccinated person was spared infection.

Same scenario in Colorado where the MMR vaccination rate is 81.7%

366 vulnerable children

1634 covered.

All exposed and 329 of unvaccinated children will be sick (90% infection rate) and 45 of the covered children will be sick, again a 2.7% infection rate.  In this case however, only 12% of the sick children were vaccinated.

The more unvaccinated people walking around, the more reservoirs there are for disease and for the disease to linger and expose more people.  If very few people are unvaccinated, the disease dies out quickly, there is nowhere for it to go.  The more people that are unvaccinated, the more places there are for the disease to go, exposing more people to the virus.

      Footnotes: 54 came from. Multiplying 1994 by .97 (the effectiveness of the MMR).  1-(1994*.97)=60. 60*.90(likelihood of getting measles once exposed)=54.