Vaccination of influenza a virus decreases transmission rates in pigs

Romagosa, Anna; Allerson, Matt; Gramer, Marie; Joo, Han Soo; Deen, John; Detmer, Susan; Torremorell, Montserrat

Pigs were both antibody and influenza virus negative at the start of the study. Table 2 shows the levels of HI antibody titers against the 4 selected flu strains prior to exposure to the seeder pigs and at necropsy. Two weeks after the second vaccination, the homologous vaccine induced robust HI titers against the challenge strain (IA04), but mean reciprocal titers in the HE group were below 1:20. In contrast, the HE group had reciprocal titers above 1:160 against the H1N1 and the H3N2 strains contained in the vaccine (IA00, NC05 and MO05), while the mean reciprocal titers in the HO group were below 1:40. At the end of the experiment, HI titers against the challenge virus remained at about the same levels in the HO group, and although a statistically significant increase in mean titers in the HE group was observed (p < 0.05), they still remained below 1:40. In the NV group, all pigs were seronegative (1< 10) before contact and at necropsy, and the lack of seroconversion at necropsy was most likely due to the limited time between infection and necropsy (less than 7 days) [36, 47] .