DNA vaccines are capable of priming the immune system of neonates in the presence of maternal antibodies. However, it is still not clear whether the extent of priming and protection against challenge infections induced by a DNA vaccine in maternally immune newborns is better than that induced by conventional vaccines. To study this, we used the pseudorabies virus (PRV) infection model in the natural host, the pig. We compared the efficacy of a DNA vaccine with the efficacy of a conventional modified live vaccine (MLV) and an inactivated vaccine (IV) in maternally immune newborn piglets. We measured the priming of the immune response and the degree of protection against challenge infection for all vaccine types. We vaccinated piglets with or without maternal immunity twice, at the age of 5 and 9 weeks, and we assessed protection by challenge infection with virulent PRV at the age of 15 weeks. Vaccination with DNA or conventional vaccines induced both humoral and cell-mediated immune responses in maternally immune animals. DNA vaccination seemed not to suffer from suppression by maternal immunity and resulted in similar or stronger immune responses in maternally immune piglets as compared in naïve piglets. In contrast, vaccination with conventional vaccines resulted in weaker immune responses in maternally immune piglets than in naïve piglets. Moreover, DNA vaccination provided better protection against challenge infection in maternally immune piglets than in naive piglets, whereas vaccination with conventional vaccines did not. © 2005 Elsevier Ltd. All rights reserved.
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