Evaluation of A/New Jersey/76 influenza whole-virus vaccine in hysterectomy-derived pigs.

Twenty-one pigs delivered by hysterectomy from three sows were used to evaluate influenza A/New Jersey/76 virus vaccine in neonatal pigs. Pigs were vaccinated on the day of birth or at three days of age with either 200 or 400 chick cell-agglutinating (CCA) units of vaccine, and pigs were bled two and four weeks after vaccination. The 21 vaccinated pigs and two unvaccinated control pigs were challenged intranasally at five weeks of age, and nasal swabs were obtained for six consecutive days after challenge. Two weeks after vaccination, only three pigs had reciprocal hemagglutination-inhibiting (HAI) antibody titers of greater than or equal to 20. Four weeks after vaccination, 11 pigs had HAI titers of greater than or equal to 20, and titers of virus-neutralizing antibody ranged from less than 10 to 1,000 among these same sera. On day 7 after challenge, 12 pigs had HAI titers of greater than or equal to 20. Swine-like influenza virus was isolated from nasal swabs from the controls and from four of the 21 vaccinated pigs. The results indicated that 80% of the vaccinated pigs were protected.