Mumps math
Apr. 13th, 2006 10:06 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
mmcirvinThe first thing a lot of people probably wondered when hearing about the Iowa mumps outbreak, and especially the number of vaccinated people who got the mumps, was "does this mean the vaccine doesn't work?"
Mark Chu-Carroll and Tara Smith run the numbers. The answer is that the outbreak's consistent with the vaccine working about as well as previously thought. This isn't some kind of super-mumps.
Most of the people who got it were vaccinated. How can this be consistent with the vaccine protecting most of the people who get it? It can be if not many people were unvaccinated in the first place.
Here's an unrealistic toy model even simpler than Tara's. Suppose there are 100 people and 98 of them get their shots. Of the 98, say 90 of them develop antibodies and are immune—an over 90% rate of effectiveness for the vaccine. Then we've got 10 people who are unprotected: 8 who got the vaccine and 2 who didn't. If they all got sick (that's unrealistic virulence, but it shouldn't change the percentages), 80% of the infected would be vaccinated, even though 90+% of the vaccinated are immune.
In reality, the vaccine coverage rate in Iowa is lower than 98%, though different sources of information seem to disagree on the details. But, as the discussion in Mark's comment thread points out, the biggest potential tinderboxes for disease outbreaks—college campuses—also have relatively high vaccine coverage; the people least likely to get vaccinated also tend to be more isolated.
Mark Chu-Carroll and Tara Smith run the numbers. The answer is that the outbreak's consistent with the vaccine working about as well as previously thought. This isn't some kind of super-mumps.
Most of the people who got it were vaccinated. How can this be consistent with the vaccine protecting most of the people who get it? It can be if not many people were unvaccinated in the first place.
Here's an unrealistic toy model even simpler than Tara's. Suppose there are 100 people and 98 of them get their shots. Of the 98, say 90 of them develop antibodies and are immune—an over 90% rate of effectiveness for the vaccine. Then we've got 10 people who are unprotected: 8 who got the vaccine and 2 who didn't. If they all got sick (that's unrealistic virulence, but it shouldn't change the percentages), 80% of the infected would be vaccinated, even though 90+% of the vaccinated are immune.
In reality, the vaccine coverage rate in Iowa is lower than 98%, though different sources of information seem to disagree on the details. But, as the discussion in Mark's comment thread points out, the biggest potential tinderboxes for disease outbreaks—college campuses—also have relatively high vaccine coverage; the people least likely to get vaccinated also tend to be more isolated.
![[identity profile]](https://www.dreamwidth.org/img/silk/identity/openid.png){kind=small}
no subject
Date: 2006-04-14 04:08 am (UTC)no subject
Date: 2006-04-14 05:49 am (UTC)