Assessment of effectiveness of a foot-and-mouth disease vaccine in cattle in Ethiopia

This study was aimed at evaluating the field effectiveness of a trivalent foot and mouth disease
(FMD) vaccine (containing serotypes O, A and SAT 2), produced and widely used in Ethiopia, in
terms of preventing clinical infection and severe disease.
A randomized controlled trial design was employed in the study in which the attack rate of clinical
FMD infection in vaccinated cattle was compared with the attack rate in unvaccinated controls in
cattle population of 16 villages in Gondar Zuria district, Northwest Ethiopia. The vaccine was
administered as a single dose course in the face of an impending FMD outbreak and the trial groups
were monitored for clinical infection until the end of the outbreak.
The attack rate of clinical FMD in the vaccinated cattle (34%) was significantly lower than the attack
rate in unvaccinated controls (49%) (p< 0.001). However, the effectiveness of the vaccine was only
31% (95%CI: 20 - 40%). The proportion of severely affected cattle in the vaccinated group (5.7%)
was significantly lower than in the unvaccinated group (9.4%) (p< 0.001), resulting in 39% (95%CI:
18-55%) vaccine effectiveness against severe disease.
The observed level of vaccine effectiveness was lower than the internationally recommended 70%
expected percentage of protection for a standard potency 3PD50/dose FMD vaccine. Moreover, the
level of effectiveness was insufficient to provide herd immunity to control the disease at the
population level. Nevertheless, given the significant difference in the incidence of clinical disease
between vaccinated and unvaccinated cattle, it might still be cost-effective to use the current vaccine
to reduce production losses. Factors that cause low effectiveness of the vaccine need to be
identified and addressed for effective control of the disease at population level.