Herd Immunity Explained

When you understand how viruses need a certain sized Petri dish of human population to survive, and if you take away that number through herd immunity—post-infection immunity, vaccine—then you take away that infection’s fidelity. Vaccines are given not just for individuals; they are given as a public health measure. When you and I go get our annual flu vaccine, or we have our children obtain all their childhood shots, we are doing it and we think we are doing it for ourselves or for our children. As an individual, we much prefer our loved ones and ourselves not be ravaged with the coming year’s flu. And that is true, we are desirous of not getting ill.

But the other reality is, we are also a part of a larger group of responsible citizens attempting to minimize the flu within our community, attempting to prevent an epidemic. If you immunize a statistical number of people within a given population with the flu vaccine—or nearly any vaccine for that matter—and you add to that those who had the flu, you have achieved herd immunity, you are taking away or are attempting to take away the viral breeding ground. Vaccines reflect the Spock Principle from Star Trek: The needs of the many outweigh the needs of the few, which outweigh the needs of the one.

Another way of looking at immunizations, when you were vaccinated or your children are vaccinated with the seasonal flu vaccine, or the mumps-measles-rubella MMR vaccine as well as the polio vaccine and the diphtheria-pertussis-tetanus DPT vaccine, you are not only attempting to prevent viral disease in yourself and your loved ones, which is all well and good; you also are a member of a community with social obligations attempting to prevent an epidemic. It is a social contract we have with each other.

The magic number seems to be around 80%. If eight in ten people are immune to a pathogen, especially viral buggers, the scoundrel won’t be able to find its next victim. As the image shows, those red-hot with a virus won’t spread infection if the herd in gray are immune.