why vaccinated kids get those diseases

[tenar]

I was reading the threads in this section, mulling the whole vaccination thing again, and I came across quite a few people wondering, or commenting, on the fact that some of the kids that are vaccinated get the diseases they are vaccinated against.

In fact, the chances are that more kids that are vaccinated get those diseases than kids that are not vaccinated. So, being a mathsy-type of a person, I thought I'd have a go at explaining this effect to people who are curious.

It comes down to the fact that since most kids are vaccinated, most of the kids that get sick are vaccinated. However being vaccinated does actually protect a kid against that disease (not commenting here on other pros and cons of vaccinations - that isn't the purpose of this post at all).

Here's how it works:

Suppose there is a disease called thingyitus (yep, I made that up, because I don't want to get into a debate with anyone about whether specific numbers for specific diseases are wrong or right).

Suppose that vaccination for this disease has an 80% success rate (I think this is on the low side for most, not for things like the chickenpox vaccine, AIUI), by which I mean that 20% of the kids who are exposed to the disease, who are vaccinated, will catch it. Suppose that half of the kids who are exposed to the disease, who are not vaccinated, will catch it.

Suppose that 90% of kids in a school are vaccinated against thingyitus, and 10% aren't.

OK, if this disease goes around the school, and there are 100 kids in the school, what will happen is this:

90 kids are vaccinated, and 20% of them, or 18 kids, will catch thingyitus.

10 kids aren't vaccinated, and half of them, or 5 kids, will catch thingyitus.

So you can see that more of the kids who get sick are vaccinated than not.

It kinda looks like being vaccinated makes a kid more likely to get the disease. But that isn't the case at all.

5 out of 10, or 50% of the unvaccinated kids got sick.
18 out of 90, or only 20% of the vaccinated kids got sick.

Each unvaccinated kid had 2.5 times the risk of getting sick, compared to a vaccinated kid.

Now, I've chosen random and round numbers here. In practice I suspect that more than 90% of children are vaccinated for most things, depending on where you are. So the results would probably be more skewed than that.

The reason more vaccinated kids get sick than unvaccinated kids is simply because were are so many more vaccinated kids around.

So in this case, a total of 23 kids out of 100 got sick. The more unvaccinated kids you have, the more kids will get the disease. If half the kids were unvaccinated, there would have been 35 kids get it in total, (leaving out the details of herd immunity, which this calculation is too simple to include). If no kids were vaccinated, there would have been 50 kids get the disease, and if all kids were vaccinated there would have been 20 kids get the disease.

I hope that this explanation and example helps people understand this point better.

Tenar.

[paradise lost]

Thanks for that Tenar. I just want to add that the reason some kids still get the disease is that there immune system doesn't react as expected to the vaccine. The smallpox vaccine used dead cowpox cells. These cells were dead (harmless) and cowpox itself was not anything like as dangerous to people as smallpox. It was found that when you injected dead cowpox cells into someone their immune system forms antibodies against it. Then if the person is exposed to smallpox the body recognises it, because it's so similar to the cowpox, and it sends the antibodies it already made to deal with it. If the vaccine takes well the person will not contract the disease at all, if it takes but not very well, the person might contract the disease but will not become as ill as they might have, because although the antibodies they formed at vaccination don't offer complete protection, they give the body a head-start on fighting the disease.

This is why children who have had the chickenpox vaccine but still contract chickenpox often end up having a very mild episode with only a mild temp, a few days of being under the weather, and only a few blisters.

Certain people's immune systems do not respond as expected to vaccines and do not form the antibodies (that's why some vaccines use live cells of the disease which have been chemically or genetically disabled rather than dead cells or cells of a similar disease - to make the body more likely to react in the desired way). In the same way that some people's bodies don't react as expected to analgesia, some do not to vaccinations. There have been some studies in Africa that suggest that it is the absence of parasites in our systems which causes allergies and autoimmune problems. The evidence is still growing as there are not too many communities of adults who were fully vaccinated as children, but early results suggest that children who are fully vaccinated have a far lower chance of having excema, asthma, or food/environmental allergies if they have had repeated or prolonged exposure to roundworm, tapeworm or hookworm.

Bx

[BellyBelly]

What about side effects of the vaccines due to what is contained in the vaccine? The kids who are not vaccinated - 0%.

[tenar]

Thanks Hoobley, I don't know much detail about the reasons why the vaccinations aren't 100% effective, but that makes perfect sense. I certainly didn't know that kids who are vaccinated have a lower risk of athsma etc, and would be interested to see a report of that research, as far as it goes.

Kelly, I was intentionally not getting into that stuff, just explaining the mathematical workings of this particular counter-intuitive thing. Of course any parent needs to weigh up the risk of the child having the disease against the risk of getting a side effect - that's the basis of the entire debate.

[Trillian]

But then you don't add in those vaccinated children who will contract the illness, but yet not actually get sick, so they become a carrier of the illness and pass it on to those who are unvacinated - be it children or adults. The thought that vaccinated children can become disease carriers tends to worry me a little more than unvaccinated people.

[Phteven]

Unvaccinated people can also be disease carriers a-la Typhoid Mary.

[BeautifulMadness]

my 22 mth old son has the measles, but thanks to having him vaccinated he didnt get as bad and im greatful for that. cause it coulda caused him serious harm.

everyone is different and reacts to things differently but thats life. but i think if u can why not help you're child/ren not get it in the first place which could KILL them when u can prevent it.

Hobbley i am with u, well said

P.S sorry if it sounds bully like, ( i need chocolate)