Why Did the WHO Alter Its Definition of “Herd Immunity?”

3 min readDec 23, 2020
Photo by Viktor Forgacs on Unsplash

Herd Immunity. Even non-science types have a vague idea of what it means. Most of us realize it refers to the protection from viral infections when a large percentage of the population obtains immunity to it. A large immune population helps prevent the spread of the virus. But how is that immunity achieved?

According to the World Health Organization (WHO), the methods to obtain herd immunity used to be found on this web page. The page, titled Coronavirus Disease (Covid-19): Serology and dated 9 June, 2020, can be found on the Web Archive (Wayback Machine): https://web.archive.org/web/20201101161006/https://www.who.int/news-room/q-a-detail/coronavirus-disease-covid-19-serology

According to the WHO, on June 9, 2020, herd immunity was defined as

“the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection.” (all emphasis mine)

An accurate and accepted definition, one that concurs with almost every other explanation on the internet and in every basic biology book I’ve ever seen.

Now compare this with the explanation currently on the same page as of 13 November, 2020. (https://www.who.int/news-room/q-a-detail/coronavirus-disease-covid-19-serology)

Now, the WHO states that herd immunity is:

a concept used for vaccination, in which a population can be protected from a certain virus if a threshold of vaccination is reached.

What happened to that other part? You know, the part about herd immunity being developed through previous infection?

Furthermore, they state that:

Herd immunity is achieved by protecting people from a virus, not by exposing them to it.”

Again, where’s the acknowledgement that herd immunity can be, and has been, established…