Yesterday, I tried to show in the most simple mathematical terms that the risk of contracting measles, in the New York City outbreak, was 30X higher in unvaccinated children than it was for vaccinated. I knew I vastly underestimated the actual rate because I used a larger population than I should, because I lacked the more specific geographic spread of the disease. I’ll leave that to a peer-reveiwed paper that I’m sure will be published in the next few months that will accurately describe everything about the outbreak. Don’t hold your breath vaccine deniers–their conclusions will only vary from mine because they’ll present a much higher risk of contracting measles amongst non-vaccinated children.

Someone suggested that I discuss another article that analyzed a measles outbreak in Corpus Christi, TX, which compared those who were vaccinated with the MMR vaccine to those weren’t. The results are clear and relatively straightforward:

1732 children were seropositive (meaning they had antibodies to measles) and over 99% of them were vaccinated. None, and not close to none, but absolutely 0 of these children contracted measles.

74 children were seronegative (they lacked measles antibodies). Fourteen (14) of these children contracted measles.

So, let’s look at the math. All of the kids who had measles antibodies (presumably as a result of the MMR vaccine, since 99% were vaccinated) avoided the disease and its consequences. On the other hand, 18.9% of the children who lacked antibodies got sick.

Again, if this isn’t clear…0% contracted the disease if they had antibodies from vaccines, 18.9% contracted the disease if they didn’t have antibodies.

Now, the 74 children who were seronegative also were vaccinated (though the paper did not tell us how many vaccines were given, it takes at least 2 to confer full immunity). If there are no other issues (and again, the article didn’t report that) like some type of compromised immune systems in some of the 74 children), the vaccine was 96% effective in seroconverting and preventing measles.

This story is rather basic. The MMR vaccine is extremely effective in boosting the immune system to produce anti-measles anti-bodies. A small group seems to have not seroconverted for unknown reasons. But even though most of the population in this study were protected against measles, the disease is so pervasive, so pathogenic, even a small group of susceptible individuals can catch it. But because the vast majority, 96% were protected against the disease, this measles outbreak didn’t spread further.

But think about this. If the number isn’t 96%, but 70% because parents refuse to vaccinate. What happens is that the random chance that an infected child encounters an unvaccinated child increases dramatically, increasing the risk of a much larger outbreak. With all of the consequences of measles.

As I said before, it really is simple math. So simple that a vaccine denier could do it.

Use the Science-based Vaccine Search Engine.

Key citation:

Gustafson TL, Lievens AW, Brunell PA, Moellenberg RG, Buttery CM, Sehulster LM. Measles outbreak in a fully immunized secondary-school population. N Engl J Med. 1987 Mar 26;316(13):771-4. PubMed PMID: 3821823.

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