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

In our experiment, a SIR model (Susceptible-Infective-Removed (or Recovered)) was used to describe influenza transmission in pigs because the disease confers immunity against re-infection with a homologous strain [44] . Basically, three different methods have been used to calculate the infection parameters based upon experimental data: Generalized Linear Models (GLM) [45, 49] , Martingale Estimations [16] , and Maximal Likelihood Estimation based on the final size of an outbreak (FS) [32, 50] . The selection of one of the three approaches depends on the data available and the intensity of the sampling. We focused on quantifying the effect of vaccination on the susceptibility of contact pigs to influenza infection instead of evaluating the effect on infectivity of vaccinated pigs. Transmission depends on both the infectivity of the infected individuals and the susceptibility of the contact pigs. In our study, we predicted that vaccination of the seeder pigs would have influenced the number of excreted influenza A viruses as shown in previous studies [30, 35] , and therefore we would not have been able to replicate conditions of transmission relevant to field situations where introduction of shedding animals in vaccinated populations is common. Nevertheless further studies are needed to determine the effect of excretion on the infectivity of influenza vaccinated pigs.