This recombinant virus has previously been shown to protect mice against lethal challenge with PR8. The third study provided evidence that sequential use of such MVA recombinants containing inserts from two strains of influenza virus, given two months apart, still generated appropriate immune responses to the different inserts. Introduction Swine influenza is a major respiratory problem in swine.
Infected herds are common and widespread.
Moreover, there are several antigenically distinct subtypes of the causative virus that can produce disease in susceptible pigs. There is only one vaccine available commercially, an inactivated product derived from a single strain, which does not provide protection against all virulent strains. The potential advantages of a SIV recombinant vaccine are that it may express protective immunogens against even the most virulent of viruses in a safe vector, provide both humoral and cell-mediated immunity, and extend the duration of that protection beyond the time provided by an inactivated product. A live virus vaccine could generate these elements of protection. However, the ability of influenza virus to infect numerous species, including humans, and to mutate and to undergo genomic reassortment, causes reluctance to introduce live strains into a susceptible population.