Vaccine herd effect

Figures & data

Figure 1. Schematic presentation of the herd effect: The index patient transmits an infectious agent to a given number (basic reproductive number R₀) of susceptible persons in the community. Black circles are infected persons and white circles are uninfected susceptible persons (panel A). After a mass immunization programme in the community (panel B), a proportion of the population is immunized (grey circles with ‘I’), thus directly protected from the infectious agent (direct effect). The immunized individuals further protect the susceptible population (white circles with ‘H’) by stopping the transmission within the social networks. This extra protection effect provided by a vaccine is called ‘herd immunity’.

Figure 2. The vaccine herd effect on Haemophilus influenzae type b diseases in Finland after introduction of the Haemophilus influenzae type b conjugate vaccine in 1986 (adapted from Peltola et al. [5]).

Figure 3. The vaccine herd effect on invasive pneumococcal diseases in the USA after introduction of the 7-valent pneumococcal conjugate vaccine in children aged < 2 y in 2000 (adapted from Whitney et al. [21]).

Figure 4. The vaccine herd effect on influenza in a randomized control trial in Canada (adapted from Loeb et al. [32]).

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