Sunday, November 01, 2009

Herd Immunity

I've written three earlier posts about vaccinations. A few October news articles can help me elaborate.

There is an effect nicknamed herd immunity that can allow vaccines to protect even the unvaccinated. Depending upon the disease, if enough people are immune then the disease lacks a large enough pool to stabilize.

For example, rubella is not very contagious, so if 80% of the population is immune then rubella cannot prosper with only 20% available to attack. Measles is quite contagious, so 95% of the population needs to be immune to squeeze out measles.

Now, H1N1 is so amazingly contagious that I doubt we can hope for herd immunity. We'd need more than 95% immune but sometimes vaccinations don't cause enough of an immune response to work, and some people are not candidates for vaccination.

Also, some diseases don't need to be fought with mass vaccinations. For example, chicken pox is not very dangerous to most kids and suffering through the disease provides a much more thorough immune system response than a shot. That's why parents of normally healthy kids have for generations been using "chicken pox play dates" instead of vaccinating against chicken pox.

But let's ignore H1N1 and chicken pox. This essay's point is that vaccinations like the MMR are enough to create herd immunity, and those three diseases are dangerous enough that parent's certainly don't want to use "measles play dates" instead of a shot!

That's why it's a problem when too many parents opt out of vaccinating their children. By ruining herd immunity, their choice is putting other people at risk. It's especially sad because their choice is often based on prejudice and ignorance.

I would not want government to require vaccinations, but I fear something like a resurgence of measles will happen before vaccinations are no longer villified.

H1N1 might cause the social change despite the fact it's probably not able to be fought with herd immunity. Americans are seeing many young people die within a few months (usually due to complications, not H1N1 by itself). As a culture we're not used to being culled. Our people in poor health generally either take medications to keep living reasonably well, or die at a slow rate. Seeing many people simultaneously suffer and die has not happened for a few decades. Now our illusion of health entitlement is shattering.

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