Definition of Herd Immunity changed

https://web.archive.org/web/20201022012953/https://www.who.int/news-room/q-a-detail/coronavirus-disease-covid-19-serology

Herd immunity is the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection. This means that even people who haven’t been infected, or in whom an infection hasn’t triggered an immune response, they are protected because people around them who are immune can act as buffers between them and an infected person. The threshold for establishing herd immunity for COVID-19 is not yet clear. 

https://web.archive.org/web/20201114155111/https://www.who.int/news-room/q-a-detail/coronavirus-disease-covid-19-serology

‘Herd immunity’, also known as ‘population 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.