The use of immunization programs in wild populations: Modelling effectiveness of vaccination campaigns against rabbit hemorrhagic disease

Vaccination programs are occasionally used on wild mammal populations with conservation goals. In the case of the European wild rabbit Oryctolagus cuniculus, vaccination campaigns against rabbit hemorrhagic disease (RHD) have been widely applied to enhance rabbit populations, but their overall effects have not been compared. I used a modelling approach to compare the effects of several vaccination strategies on the growth rate of wild rabbit populations. For all simulated vaccination strategies, vaccination campaigns yielded positive or negative population growth rates, depending on rabbit population dynamics and subsequent RHD dynamics. Growth rate was negative when the proportion of RHD-seropositive adult rabbits was low or medium before vaccination, which occurred in populations at low rabbit density. Given that these low density populations are mainly targeted by vaccination campaigns, the model suggested that current immunization programs may be causing harmful effects on many rabbit populations. The best annual period to carry out vaccination campaigns was determined by the age-class targeted for immunization. If the RHD dynamics were not known, vaccination of only juvenile rabbits seemed to be the most conservative option, since it minimized the probability of yielding negative growth rates, whereas vaccination of only adult rabbits was the worst option. These findings suggest that prior knowledge of RHD dynamics in populations subject to immunization is essential to minimize the risk of harmful effects.