Statistical analysis
SECONDARY
Change in FLU-PRO Plus total score (AUC) through Day 7 was a secondary trial endpoint, formally tested with an alpha level of 5% (two-sided) after adjustment for multiplicity using a pre-specified testing hierarchy (Fig. S1 in Additional file Subgroup analyses by symptom severity were adjusted for treatment, baseline value, age group, duration of symptoms group, sex, and region, along with a treatment by subgroup interaction term.Missing data, which were mostly due to challenges with electronic questionnaire software, failure to complete paper questionnaires, or lost-to-follow-up data, were imputed using a modified last-observation carried forward approach for the final assessment only (i.e., Day 7, Day 14, or Day 21). If a FLU-PRO score was missing, the last non-missing, post-baseline score from that week (i.e., Day 2–6 for missing Day 7, Day 8–13 for missing Day 14, and Day 15–20 for missing Day 21) was carried forward as the Day 7/14/21 score. If no non-missing score was available, no score was imputed and the AUC was not calculated.Time to sustained (≥ 48 h) symptom alleviation was analyzed using the Kaplan–Meier methods and a log-rank test stratified by region, duration of symptoms group, age group, and sex.For the exploratory endpoints of WPAI and SF-12 Hybrid, mean change in scores were summarized and no formal statistical analysis was conducted.