In a shocking reversal that’s akin to redefining reality, the World Health Organization has changed its definition of herd immunity. Herd immunity occurs when enough people acquire immunity to an infectious disease such that it can no longer spread widely in the community.
When the number susceptible is low enough to prevent epidemic growth, herd immunity is said to have been reached. Prior to the introduction of vaccines, all herd immunity was achieved via exposure to and recovery from an infectious disease.
