Difference in Differences analysis evaluates the effects of the Badger Control Policy on Bovine Tuberculosis in England

Persistent tuberculosis (TB) in cattle populations in England has been associated with an exchange of infection with badgers (Meles meles). A badger control policy (BCP) commenced in 2013. Its aim was to decrease TB in cattle by reducing the badger population available to provide a wildlife reservoir for bovine TB. Monitoring data from 52 BCP intervention areas 200-1600 km2 in size, starting over several years, were used to estimate the change in TB incidence rate in cattle herds, which was associated with time since the start of the BCP in each area. A Difference in Differences analysis addressed the non-random selection and starting sequence of the areas. Herd incidence rate of TB reduced by 56% (95% Confidence Interval 43-67%) up to the fourth year of BCP interventions, with the largest reductions in the second and third years. There was insufficient evidence to judge whether incidence rate reduced further beyond four years. These estimates are the most precise for the timing of decline in cattle TB associated with interventions primarily targeting badgers. They are within the range of previous estimates from England and Ireland. This analysis indicates the importance of reducing transmission from badgers to reduce the incidence of TB in cattle, noting that vaccination of badgers, fertility control and on farm biosecurity may also achieve this effect.