The safety of overdose and repeat administrations of BCG Danish strain 1331 vaccine in calves and pregnant heifers

Abstract

Bovine tuberculosis (bTB), caused by Mycobacterium bovis infection, is a zoonotic disease in cattle that represents a significant ongoing challenge to cattle farming productivity and the livelihoods of livestock farmers in the UK. Vaccination of cattle with BCG could directly target the ability of M. bovis to proliferate within vaccinates, restricting bTB pathogenesis and onward disease transmission, and represent a step change in the tools available to help control bTB in farmed cattle. A Marketing Authorisation (MA) is required before a cattle BCG vaccine could be sold and supplied as a veterinary medicine within the UK and this requires comprehensive data supporting vaccine quality, efficacy and, most importantly, its safety. We carried out two independent Good Laboratory Practice (GLP) studies in which the safety of BCG vaccination in cattle was stringently tested through overdose and repeat vaccine administrations in young calves and pregnant heifers. Mild and generally short-lived reactions to vaccinations were observed in some animals, most commonly increases in body temperature and swelling at vaccine injection sites, but these did not have a negative impact on the overall health status of vaccinates. BCG was not shed in the saliva, faeces, milk or urine from vaccinated animals and its dissemination was limited to injection site tissues and associated lymph nodes. Overall, young calves and pregnant heifers vaccinated with BCG remained in good general health, and the vaccinated pregnant heifers had normal pregnancies and gave birth to healthy calves. Obtaining a Marketing Authorisation for a cattle BCG vaccine is a critical milestone in the progress towards the eventual use of BCG vaccination in cattle as an additional bTB control tool within the UK; these pivotal GLP vaccine safety studies generated the detailed and essential target animal safety data needed to support this.