Group Total number Number persistently viraemic Proportion persistently viraemic Preventable fraction Canarypox-FeLV 24 4 17% 79% Leucogen 24 6 25% 68% Controls 23 18 78% -

Table 2: Preventable fraction in vaccinated groups (PF=(Pv-Pc)/(1-Pc) where Pv is the proportion of vaccinated cats which became persistently viraemic and Pc the proportion of controls which became viraemic).