RENBP and infection: For Period 1 (6 months), Period 2 (6 months) and Period 3 (12 months), 6.9%, 4.0% and 6.3% of the sero-Ag negative (naïve) individuals at risk of infection seroconverted, respectively; leading to a sero-Ag incidence rate of 6300 (100000 persons-year).