Immunization coverage required to prevent outbreaks of dog rabies

WHO recommends that 70% of dogs in a population should be immunized to eliminate or prevent outbreaks of rabies. This critical percentage (P-c) has been established empirically from observations on rite relationship between vaccination coverage and rabies incidence in dog populations around the world. Here, by contrast, we estimate P-c by using epidemic theory, together with data available from four outbreaks in urban and rural areas of the USA, Mexico, Malaysia and Indonesia. From the rate of increase of cases at the beginning of these epidemics, we obtain estimates of the basic case reproduction number of infection, R(0), in the range 1.62-2.33, implying that P-c lies between 39% and 57%. The errors attached to these estimates of P-c suggest that the recommended coverage of 70% would prevent a major outbreak of rabies on no fewer than 96.5% of occasions.