Model fit for acute episodes assessed by weighted sums of squares.

We calculated the squared difference between the trial estimate and the predicted protective efficacy, weighted them by the number of person years at risk/100 and summed them to give a measure of the goodness-of-fit. A smaller value indicates a better fit. The three trials with EIR measurements were formally used to test the models, the remaining three were used only to validate the model output against general patterns in the trial results.