Intended for healthcare professionals


Health professionals do not understand mathematical models

BMJ 2000; 320 doi: (Published 26 February 2000) Cite this as: BMJ 2000;320:581
  1. W J Edmunds, health economist (,
  2. N J Gay, mathematical modeller
  1. PHLS Communicable Disease Surveillance Centre, London NW9 5EQ

    EDITOR—The science commentary on herd immunity that accompanied the article by Panagiotopoulos et al on an increase in the occurrence of congenital rubella after immunisation seemed irrelevant.1 In this letter we attempt to explain the relevant issues.

    Immunising a proportion of the population reduces the risk of infection (not necessarily disease) among those who are not immunised. This indirect protection from infection is termed herd immunity. It can be manifested in two different ways.

    Firstly, if the level of vaccine coverage is high …

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