Figure 4.

Sensitivity of results for model-predicted persistence to the frequency of introduction of weaners on finishing farms. The probability of stochastic fade-out of infection (left) and the model-predicted mean seroprevalence of influenza prior to slaughter (right) is plotted for finishing herds ranging in size from 250 to 5000 pigs. Births and the movement of pigs from one site to the next are assumed to occur (a) weekly, (b) every three weeks, (c) every six weeks or (d) every 12 weeks. The coloured lines represent the model results for values of R₀ between 1.5 and 4, while the shaded regions between the dotted coloured lines represent the corresponding 95% prediction intervals. The black circles represent the mean seroprevalence of H1N1, H1N2 and H3N2 antibodies observed among finishing pigs from farms of varying size in The Netherlands, while the black lines are the corresponding 95% CIs.