Qu: What is herd immunity?

That’s a very topical question in recent times and, as a medical rep working in the biopharmaceutical sector, you would almost certainly need to have a keen understanding of what this term means; it’s relevance in the grand scheme of things and of course, how it’s achieved.

Well lucky for you that it forms the basis of this week’s blog, so grab yourself a coffee and read on! If you have any further questions, then you’re most welcome to email them to me and I’ll do my best to address them in more detail for you.

Technically the term ‘herd immunity’ defines the immunity or resistance to a particular infection that occurs in a group of people or animals when a very high percentage of individuals have been vaccinated or previously exposed to the infection (1).

Basically, it means that a certain number of people need to be immunized against a given pathogen for the broader community to be reasonably protected from catching it; usually around 70% (2). So, if 7 out of 10 people in a room are immune, then its far less likely that the 3 unprotected people can be exposed (because only the three of them could potentially infect each other).

People can develop immunity either through catching the disease (and developing an immune response naturally), or through vaccination (where we purposely induce it), and in most cases that immunity remains good for life. Immunization is important because we need to protect those who are most at risk from a given disease, e.g.

  • Young children (who don’t have a fully functional immune system yet)

  • The elderly (who’s immune system may no longer work very well), and

  • People who have a suppressed immune system for some other reason

The concept first came to light back in the 1930’s during a measles outbreak in which doctors noticed that as more children became infected and then recovered, the number of new infections started to decrease even in very susceptible individuals (3). At the time it was postulated that, having been infected, the recovered patients now had some ‘natural defense’ against the pathogen, meaning that it could no longer take hold, and therefore could not be passed on to others. With fewer ‘transmitters’ for the disease walking around, then fewer susceptible people can become exposed, and the infection peters out – simple!