Effect of intratracheal challenge of fattening pigs previously immunised with an inactivated influenza H1N1 vaccine.

Intratracheal inoculation of a field isolate of influenza A H1N1 caused high fever, anorexia and dyspnoea in unvaccinated pigs. In a limited study, it was shown that animals vaccinated once with an inactivated influenza A H1N1 strain showed partial protection at challenge, indicated by mild or absent clinical signs and by the suppression of viral replication. There appeared to be a correlation between the hemagglutination-inhibition titers of the serum of vaccinated pigs and the degree of protection. Animals vaccinated with two spaced injections were completely protected at challenge. Viral replication was inhibited in their respiratory tract since no virus was isolated from animals at slaughter and no increase in antibody titer was observed in challenged vaccinates followed serologically. It was concluded that vaccination of swine against influenza with an inactivated vaccine can result in a protective immunity in the respiratory tract. The New Jersey vaccine strain could protect against swine influenza strains (H1N1) currently prevalent in several European countries.