Abstract: OBJECTIVE To investigate the effect of oseltamivir phosphate capsules combined with Lanqin oral liquid on T-lymphocyte subsets in patients with H1N1 influenza virus infection. METHODS A prospective study design was adopted. A total of 146 patients with H1N1 influenza virus infection admitted to Nanjing Central Hospital from Jan. 2022 to Jan. 2025 were enrolled and divided into two groups according to the treatment regimen: control group (oseltamivir phosphate capsules, n=71) and experimental group (oseltamivir phosphate capsules + Lanqin oral liquid, n=75). After 1∶1 propensity score matching (PSM), 63 patients were included in each group. Repeated-measures analysis of variance (ANOVA) was adopted to evaluate changes in inflammatory factors and T-lymphocyte subsets, and a difference-in-differences model was applied to assess clinical symptom scores. RESULTSThe experimental group showed a higher total effective rate (95.24%) than the control group (80.95%) (χ²=6.130, P=0.013). On days 3 and 5 of treatment, the levels of tumor necrosis factor (TNF-α), C-reactive protein (CRP), interleukin (IL)-6 and IL-8 in the experimental group were lower than those in the control group, showing greater reductions (P<0.05). The levels of CD₃⁺, CD₄⁺ and the CD₄⁺/CD₈⁺ ratio were higher, while CD₈⁺ level was lower in the experimental group, indicating greater improvement (P<0.05). On day 5 of treatment, the scores for cough, headache and fatigue in the experimental group were lower than those in the control group (P<0.05). The difference-in-differences model showed that the reductions in these scores were 1.339, 1.865 and 1.475 points greater in the experimental group than in the control group, respectively. The incidence of adverse reactions was 7.94% in the experimental group compared with 4.76% in the control group, with no significant difference (P=0.465). CONCLUSIONThe combination of oseltamivir phosphate capsules and Lanqin oral liquid effectively regulates T-lymphocyte subset balance, suppresses inflammatory responses and demonstrates favorable safety in treating H1N1 influenza.