Fig 1.
Top row: Scatter plots of antibody titer level by age groups. Bottom row: Histograms of antibody titers by age groups. Red lines show the 1.5 cut-off used to define seropositivity.
Fig 2.
The nested model structure for exploring age-prevalence data for RSV using catalytic infection models.
The compartments in the model represent the following states of the population: M = Individuals with maternally acquired antibodies (split into 2, M1 and M2 to allow for improved fit), S0 = Seronegative after loss of maternally acquired antibodies, F0 = Permanent seropositive status after infection, F1 = Temporary seropositive status after primary infection, S1 = Seronegative after loss of infection acquired antibodies. When p = 0, the model reduces to MSF, when p = 1 and only 1 rate of infection is estimated (λ0 = λ1) the model is MSFSF1 and with p = 1 and 2 rates of infection estimated (λ0 ≠ λ1) the model is MSFSF2.
Table 1.
Description of the model parameters.
Table 2.
Proportion of children seropositive for RSV antibodies per age group.
Fig 3.
Plot of the nested models output compared to the data.
The MSF model fit the data best with an AICC value of 634.6, the MSFSF1 had an AICC of 635.6 while the MSFSF2 had 637.9
Table 3.
Results of fitting the three models contained in the nested model structure.
Fig 4.
Results of the MSF model fit and the confidence region.
Main: Of the three models in the nested model structure, the MSF model gave the best fit to the data and is shown by the blue line. The parameters were re-estimated to obtain the fits that gave the 95% confidence region by Bootstrapping method, grey lines. The red circles show the proportions seropositive by age group according to the data. Inset: A magnification for age range 0–3 years.
Fig 5.
MSF Model predictions of the proportions seropositive and the force of infection acting on the different ages.
The dark blue bars show the proportion at different age groups that have maternally acquired antibodies while the pink bars show the proportion that have been infected and hence have infection acquired antibodies, as predicted by the MSF model. The dashed blue line shows the stepwise force of infection function.