All opinions are my own and do not necessarily reflect those of Novo Nordisk.

When I hear about events such as the recent outbreak of measles among a small group in Texas, I am reminded of how complex, complicated and difficult public health efforts can be. In the US, for example, there are conflicting imperatives:  the rights of people to practice their beliefs versus the right of the community to be protected against preventable health threats.  This particular situation involved members of a church congregation, many of whom had not gotten vaccinated for measles due to worries about a link between autism and the Measles-Mumps-Rubella (MMR) vaccine.  While no scientific evidence has been found to support any such link, many had chosen not to be vaccinated “just in case.”

One day I hope to write about the link between the phenomenon of science denial and personal identity (one perspective can be seen here), but for now I just want to point out how this event and a recent publication by the Centers for Disease Control (CDC) on rotavirus vaccines demonstrate nicely the concept of herd immunity (article behind paywall, but writeup here).  There are different usage patterns for the term, so I’ll say up front I am using “herd immunity” to describe not just the proportion of individuals within a population who are immunized to a given pathogen but also the indirect effects for non-immunized individuals.  The term was first used in a publication in 1923, by Topley and Wilson, in the context of how to describe the host side of their studies in bacterial infection among mice.  The concept later gained mathematical underpinnings, including formulas describing how the different ratios of vaccinated to nonvaccinated individuals defines the degree of herd immunity depending upon how infectious a disease agent is. Continue reading →