Studies on the Duration of Immunity conferred by a Live-Modified Sheep Pox Tissue Culture Virus Vaccine

Abstract

Summary Three hundred young and healthy sheep were used to study the duration of immunity of a modified live virus sheep pox vaccine. Experimental sheep vaccinated with the test vaccine resisted a challenge dose of virulent virus for up to 22 months. Some apparent loss of protection occurred after 24 months. Four large flocks of 4,330 sheep were vaccinated and remained healthy for up to 24 months when pastured in areas where non‐vaccinated sheep contracted the disease. Challenge is the method of choice for evaluating immunity. There was poor correlation between SN and CF tests and immunity produced by the test vaccine. These studies suggest that the resistance produced by the live modified sheep pox tissue culture vaccine may last beyond the 24 months observation period. Zusammenfassung Untersuchungen über die Dauer der Immunität nach Impfung mit einer Schafpocken‐Lebendvaccine aus modifiziertem Kulturvirus 300 junge, gesunde Schafe, die mit einer Lebendvaccine aus modifiziertem Schafpocken‐Kulturvirus geimpft worden waren, wurden zur Untersuchung der Immunitätsdauer eingesetzt. Experimentell mit der Versuchsvaccine geimpfte Schafe widerstanden bis zu 22 Monaten einer Testinfektion mit virulentem Schafpockenvirus. Ein merklicher Immunitätsrückgang trat nach 24 Monaten ein. Vier größere Herden mit insgesamt 4330 Schafen wurden ebenfalls geimpft. Sie blieben 24 Monate lang gesund, nachdem sie in Gebieten geweidet worden waren, wo nichtgeimpfte Schafe von der Seuche befallen wurden. Die Testinfektion ist die Methode der Wahl zur Prüfung der Immunität. Es ergaben sich kaum Beziehungen zwischen den Ergebnissen von Serumneutralisation und Komplementbindungsreaktion einerseits und der durch die Lebendvaccine hervorgerufenen Immunität. Auf Grund der Untersuchungen kann angenommen werden, daß die durch die Schafpocken‐Lebendvaccine aus modifiziertem Kulturvirus bewirkte Immunität noch über die Beobachtungsperiode von 24 Monaten hinaus anhalten dürfte. Résumé Recherches sur la durée de l'immunité après vaccination avec un vaccin vivant contre la variole ovine, préparé avec un virus modifié On emploie 300 moutons jeunes et sains pour vérifier la durée de l'immunité obtenue avec un vaccin vivant préparé avec un virus modifié de la variole ovine. Les moutons vaccinés expérimentalement avec ce vaccin sont protégés pendant 22 mois contre une infection test avec du virus virulent de la variole ovine. On observe un affaiblissement sensible de l'immunité après 24 mois. On vaccine également quatre troupeaux plus importants, comprenant 4330 moutons. Ces derniers sont restés pendant 24 mois en bonne sonté, après avoir été dans des pǎturages où des moutons non vaccinés avaient subi l'épizootie. L'infection test est la méthode de choix pour vérifier l'immunité. On ne trouve pratiquement pas de relations entre les resultats de la neutralisation du sérum et de la réaction de fixation du complément d'une part et d'autre part l'immunité induite par le vaccin vivant. Sur la base de ces recherches, on peut admettre que la résistance ...

Scientific Opinion on sheep and goat pox

“…Vaccine challenge using a virulent field strain is the only method available to measure the protection provided by the vaccine (Abbas et al, 2010;Ramyar and Hessami, 1970) Because of the cell-mediated immunity against SPPV, not all vaccinated animals produce detectable antibody levels, although they would be fully protected against the disease (Kitching, 1986). Vaccine challenge using a virulent field strain is the only method available to measure the protection provided by the vaccine (Abbas et al, 2010;Ramyar and Hessami, 1970) Because of the cell-mediated immunity against SPPV, not all vaccinated animals produce detectable antibody levels, although they would be fully protected against the disease (Kitching, 1986).…”

“…The safety and efficacy of the strain were evaluated by Ramyar and Hessami (1970) using 300 naive Baluchi sheep, six to nine months of age. Each dose of the commercially available vaccine contains a minimum of 10 -2.5 TCID 50 (tissue culture infective dose) virus.…”

“…Because SPPV and GTPV do not replicate in small rodents, there are no small animal models available to evaluate the efficacy of the vaccine. Vaccine challenge using a virulent field strain is the only method available to measure the protection provided by the vaccine (Abbas et al, 2010;Ramyar and Hessami, 1970) Because of the cell-mediated immunity against SPPV, not all vaccinated animals produce detectable antibody levels, although they would be fully protected against the disease (Kitching, 1986). The combination of a local reaction at the vaccination site and an antibody response has been used as an indirect indicator for protection in cases when it has not been possible to carry out challenge experiments.…”

“…Live attenuated vaccines have been used for decades in SPP-endemic countries. Sufficiently attenuated and tested vaccines are safe (can be used in pregnant animals providing three months of immunity to lambs) and effective though some strains may have unacceptably high levels of residual pathogenicity and may cause skin lesions and generalised disease in some animals (Ramyar and Hessami, 1970;Yogisharadhya et al, 2011). Local reaction at the inoculation site and transient raise in body temperature are typical of live attenuated poxvirus vaccines and should be accepted as an indicator of virus replication, which is required for the production of strong cell-mediated immunity in vaccinated animals (Carn, 1993).…”

“…The safe attenuation of this strain requires a minimum of 30 passages. The safety and efficacy of the strain were evaluated by Ramyar and Hessami (1970) using 300 naive Baluchi sheep, six to nine months of age. The intradermal route (ID) of administration (120 sheep) was compared with the subcutaneous (SC) route (120 sheep).…”