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To aid understanding of the effect of antiviral treatment on population-level influenza transmission, we used a novel pharmacokinetic-viral kinetic transmission model to test the correlation between nasal viral load and infectiousness, and to evaluate the impact that timing of treatment with the antivirals oseltamivir or baloxavir has on influenza transmission. The model was run under three candidate profiles whereby infectiousness was assumed to be proportional to viral titer on a natural-scale, log-scale, or dose-response model. Viral kinetic profiles in the presence and absence of antiviral treatment were compared for each individual (N = 1000 simulated individuals); subsequently, viral transmission mitigation was calculated. The predicted transmission mitigation was greater with earlier administration of antiviral treatment, and with baloxavir versus oseltamivir. When treatment was initiated 12-24 hours post symptom onset, the predicted transmission mitigation was 39.9-56.4% for baloxavir and 26.6-38.3% for oseltamivir depending on the infectiousness profile. When treatment was initiated 36-48 hours post symptom onset, the predicted transmission mitigation decreased to 0.8-28.3% for baloxavir and 0.8-19.9% for oseltamivir. Model estimates were compared with clinical data from the BLOCKSTONE post-exposure prophylaxis study, which indicated the log-scale model for infectiousness best fit the observed data and that baloxavir affords greater reductions in secondary case rates compared with neuraminidase inhibitors. These findings suggest a role for baloxavir and oseltamivir in reducing influenza transmission when treatment is initiated within 48 hours of symptom onset in the index patient.

Abstract Baloxavir marboxil is an endonuclease inhibitor indicated for the treatment of influenza in patients ≥12 years. No data exist for Chinese patients in global studies. This randomized, open‐label, phase I study evaluated the pharmacokinetics (PK) and safety of baloxavir marboxil in healthy Chinese volunteers and was used to anticipate efficacy in Chinese patients. Patients received a single oral dose of baloxavir marboxil (40 or 80 mg [1:1]). Serial blood samples were collected predose and at various timepoints up to 14 days postdose. Baloxavir marboxil and acid plasma concentrations were determined by liquid chromatography tandem mass spectrometry. PK parameters of baloxavir acid were estimated by noncompartmental analysis. Adverse events (AEs) were recorded. Time to alleviation of symptoms (TTAS) was simulated for otherwise healthy (OwH) and high‐risk (HR) Chinese and Asian patients. Thirty‐two male patients received baloxavir marboxil. Baloxavir acid plasma concentration peaked 4 h postdose. Mean maximum concentration (Cmax) was 107.6 and 206.9 ng/ml, and mean area under the plasma concentration‐time curve from zero to infinity (AUC0–inf) was 6955 and 9643 ng·h/ml in the 40 and 80 mg cohorts, respectively. AEs were mild and transient; no new safety signals were identified. Simulated median TTAS for OwH and HR Chinese patients agreed with simulated values in Asian patients. PK parameters were similar to Asian populations in other studies. The globally adopted baloxavir marboxil dosing strategy was consistent with the established safety profile of baloxavir marboxil in this population. Simulated efficacy indicated Chinese patients could benefit from similar efficacy to Asian patients.