A recent news report about the Covid-19 pandemic states that “Herd immunity means letting a large number of people catch a disease, and hence develop immunity to it, to stop the virus spreading.”
This concept of herd immunity has become popular and even dominant, judging from my social media feeds. If this is so, it represents a real loss. Apart from its striking internal contradiction, this understanding of herd immunity distorts and, I dare say, besmirches a perfectly good idea from the health sciences.
Let us talk about the internal contradiction first. ‘Letting a large number of people catch a disease’ means the same thing as ‘letting the virus spread’. The virus spreads from a sick person to a healthy person by making the healthy person ‘catch the disease’. You cannot, therefore, ‘stop the virus spreading’ by ‘letting a large number of people catch [the] disease’. It would be like dunking someone in water to stop them from getting wet.
Secondly, in the health sciences herd immunity simply refers to a situation where enough individuals in a group have immunity against a disease to prevent an epidemic of that disease in the group. This certainly implies that health practitioners would strive to establish herd immunity, but it does not mean at all that they would ‘let a large number of people catch the disease’. The concept itself does not say anything about the methods the health practitioners would use.
There is nothing in the scientific understanding of herd immunity that implies the sinister heartlesness with which the concept has become associated. If we want to avoid Covid-19 releated deaths, we would definitely want herd immunity.