Figure 2.

Epidemiological evidence of herd immunity induced by aP vaccines: decrease of cases in infants. (a) Yearly incidence (per 100 000) in infants less than 1 year old after the 1996 introduction of aP in Sweden (data redrawn from table 3 in [34]). (b) Mean yearly number of cases before (years 1992–1994) and after (overall period 1996–2011 or outbreak years) introduction of aP in Sweden, stratified by month of age in the first year of life. (c) Yearly cases per doctor in infants less than 1 year old after the 1981 introduction of aP in Japan (adapted from fig. 3 in [35]). (d) Yearly incidence (per 100 000) in infants less than 1 year old in Italy (adapted from fig. 5 in [36]).