Herd immunity is referred to when we justify mass approach in vaccination. Particularly it applies to vaccination against communicable diseases with high potential to spread. 

‘‘Herd Immunity’’: A Rough Guide is an article that provides brief historical, epidemiologic, theoretical, and pragmatic public health perspectives on this concept.

Authors: Paul Fine, Ken Eames, and David L. Heymann Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom 

Clinical Infectious Diseases 2011;52(7):911–916