eLife assessment
Illingworth et al. investigate the effectiveness of ribavirin and favipiravir on the treatment of a paediatric patient with chronic RSV and identify an increase in mutations caused by ribavirin while favipiravir had no apparent mutagenic effect. Strength of evidence is incomplete for the mathematical model and solid for the mutational load analysis with potential for improvement in both cases with clarification of the methods. Major strengths are an interesting hypothesis and appropriate modeling methodology that will be of interest to virologists, clinicians and evolutionary biologists. Weaknesses in methodology pertain to mutational load measures possibly also capturing clonal expansion of new mutants and lack of clarity about how viral fitness is related to viral load in the mathematical model.