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

Under the specific conditions of this study and as expected, influenza virus spread quickly among non- vaccinated pigs, and the estimated R 0 in this population was high (10.66, 95% CI 6. 57-16.46) . The estimated R values in the vaccinated groups were significantly different from the values in the NV group. In the HO vaccinated group R was estimated at 0, and in the HE group R ranged from 0.32 to 1.8, with an overall estimate of 1 (95% CI, 0.39-2.09). However, R in the HE group was not statistically significant below 1. Furthermore, statistically significant differences could be observed in the transmission rates (β) between replicates, showing the variability of the pigs' response to influenza vaccination. Despite the fact that transmission was significantly reduced in the HE group, we cannot exclude the possibility that outbreaks of influenza could occur in heterologously vaccinated populations as evidenced by the results of the stochastic model in this study and the modeling estimates presented by de Jong et al. [49] . On the other hand, transmission of the virus could not be detected in the HO vaccinated pigs during the study and R values in all replicates were significantly below 1, suggesting that infection spread in a population vaccinated with a homologous vaccine could be prevented.