Herd immunity

The figure below is adapted from an article published in 2011 by Fine and colleagues (). The article discusses the concept of “herd immunity”: individuals with immunity against a disease act as a “shield” for the community, slowing or stopping the spread of the disease.

At the top of the figure, the number of infected individuals grows exponentially, until a certain number of individuals with immunity is achieved. At the bottom of the figure, those with immunity “absorb and kill” the infectious agent, without passing it forward – significantly limiting the progression of the disease.

This illustrates the likely impact of vaccination in cases where immunity being acquired through full infection is problematic, such as with COVID-19. In these cases, vaccination would slow or stop the spread of the disease, even if only a proportion of the community is vaccinated.

That is, until the infectious agent mutates!