Determination of the onset of the herd-immunity induced by the E2 sub-unitvaccine against classical swine fever virus

For a recently developed E2 subunit vaccine against classical swine fever ( CSF), the reduction in transmission, at different moments after vaccination , was assessed by animal experiments and statistical calculations. Two expe riments were performed to estimate the reproduction ratio R. Experiment 1 c onsisted of three groups and experiment 2 of two groups each of 10 pigs. In four of these groups, all pigs were vaccinated intramuscularly with the va ccine. The pigs in the fifth group remained unvaccinated (control group). A fter treatment, half of each group was intranasally inoculated with the vir ulent CSFV strain Brescia. In the vaccine groups, the following vaccination -challenge intervals were applied: 14, 14, 10, and 7 days, respectively. Th e occurrence of (contact-) infection was determined using the E-rns ELISA. In the 7-days interval group and in the control group, virus transmission t o all contact pigs occurred, indicating R > 1. Neither in the two 2-week in terval groups nor in the 10-day interval group did contact-infections occur . Hence, the estimated R is less than one, which indicates that an epidemic would fade out. Therefore, the E2 subunit vaccine may be an efficacious to ol in a control program during an outbreak of CSF as from 10 days after vac cination. (C) 2000 Elsevier Science Ltd. All rights reserved.