Virological and clinical outcomes in outpatients treated with baloxavir or neuraminidase inhibitors for A(H3N2) influenza: A multicenter study of the 2022–2023 season

• Published in: Antiviral research 2024-04, Vol.224, p.105853-105853, Article 105853
• Main Authors: Goto, Takeyuki, Kawai, Naoki, Bando, Takuma, Takasaki, Yoshio, Shindo, Shizuo, Tani, Naoki, Chong, Yong, Ikematsu, Hideyuki
• Format: Article
• Language: English
• Subjects: Baloxavir; Clinical setting; Influenza; Oseltamivir; Variant
• ISSN: 0166-3542; 1872-9096
• DOI: 10.1016/j.antiviral.2024.105853

While clinical trials have illuminated both the virological and clinical efficacy of baloxavir for influenza and post-treatment viral resistance, these aspects warrant further study in real-world settings. In response, we executed a prospective, observational study of the Japanese 2022–2023 influenza season. A cohort of 73 A(H3N2)-diagnosed outpatients—36 treated with baloxavir, 20 with oseltamivir, and 17 with other neuraminidase inhibitors (NAIs)—were analyzed. Viral samples were collected before and after administering an antiviral on days 1, 5, and 10, respectively. Cultured viruses were amplified using RT-PCR and sequenced to detect mutations. Fever and other symptoms were tracked via self-reporting diaries. In the baloxavir cohort, viral detection was 11.1% (4/36) and 0% (0/36) on day 5 and day 10, respectively. Two isolates from day 5 (5.6%, 2/36) manifested I38T/M-substitutions in the polymerase acidic protein (PA). For oseltamivir and other NAIs, viral detection rates were 60.0% (12/20) and 52.9% (9/17) on day 5, and 16.7% (3/18) and 6.3% (1/16) on day 10, respectively. No oseltamivir-resistant neuraminidase mutations were identified after treatment. Median fever durations for the baloxavir, oseltamivir, and other NAI cohorts were 27.0, 38.0, and 36.0 h, respectively, with no significant difference. Two patients harboring PA I38T/M-substitutions did not exhibit prolonged fever or other symptoms. These findings affirm baloxavir's virological and clinical effectiveness against A(H3N2) in the 2022–2023 season and suggest limited clinical influence of post-treatment resistance emergence. •Analyzed 73 influenza A(H3N2) outpatients with longitudinal viral and clinical data.•Baloxavir cohort showed lower viral isolation rate than those of oseltamivir/other NAIs on both days 5 and 10.•Baloxavir-resistant viruses detected in 2 patients on day 5, but disappeared by day 10; with no prolonged fever/symptoms.•No significant differences in fever and symptom durations between baloxavir and other treatment groups.