Early Oseltamivir Treatment Lowers ICU Risk, Shortens Hospital Stays in Children With Influenza

Children hospitalized with laboratory-confirmed influenza who receive oseltamivir (Tamiflu; Genentech) are significantly less likely to be admitted to the intensive care unit (ICU) and tend to have shorter hospital stays than untreated children, wrote authors of a new study published in JAMA Pediatrics. The retrospective cohort study, which was led by investigators at the University of Colorado Anschutz School of Medicine and Children’s Hospital Colorado, is among the most comprehensive real-world evaluations of oseltamivir effectiveness in hospitalized pediatric patients to date. The findings arrive as national data show declining antiviral use among hospitalized children, despite consistent guidance favoring early treatment.^1-3

Study Design and Methodology

Investigators drew data from the Influenza Hospitalization Surveillance Network (FluSurv-NET), a CDC-supported, population-based surveillance system spanning 13 states. The analysis covered 8 influenza seasons, from 2014 to 2015 through 2022 to 2023 (excluding 2020-2021), and included children younger than 18 years of age hospitalized with laboratory-confirmed influenza who had a documented respiratory symptom onset date. After exclusions, 6044 cases were analyzed for the primary ICU outcome (70.2% received oseltamivir) and 7103 cases for the secondary hospital length-of-stay (LOS) outcome (80.9% received oseltamivir).¹

Using adjusted Cox proportional hazards models with oseltamivir receipt as a time-dependent exposure anchored to symptom onset, researchers estimated the hazard of ICU admission and hospital discharge. This approach addressed key limitations of earlier observational research, which often lacked reliable symptom-onset dates or failed to capture antiviral use initiated before admission.^1,2

Key findings

In adjusted models, oseltamivir treatment reduced the hazard of ICU admission by 31% (adjusted hazard ratio [aHR], 0.69; 95% CI, 0.60-0.80) compared with no treatment. A sensitivity analysis reclassifying same-day ICU admissions as untreated strengthened this association further (aHR, 0.30; 95% CI, 0.26-0.34). The benefit held regardless of when treatment began: both early (≤2 days from symptom onset) and late (≥3 days) initiation were associated with reduced ICU hazard versus no treatment (aHR, 0.74 and 0.55, respectively), with a persistent effect even beyond 5 days from symptom onset.^1,2

Oseltamivir treatment was also associated with a shorter hospital stay, reflected as an increased hazard of discharge (aHR, 1.13; 95% CI, 1.06-1.21). Modeled LOS was about 3.72 days for untreated patients versus 3.33 days for treated patients—a 9.4-hour reduction. Subgroup analyses found no significant difference in treatment benefit by age or presence of medical comorbidities, suggesting the benefit extends broadly across the pediatric population, including otherwise healthy children.¹

Antiviral Use Remains Underutilized

The findings arrive against a backdrop of declining antiviral use in hospitalized children. Per FluSurv-NET data cited in the study, only 63% of hospitalized children with influenza received antivirals during the 2024-2025 season, down from 86% in the 2017 to 2018 season. Separately, the CDC has flagged underuse of flu antivirals more broadly, noting that even children at higher risk for influenza complications are not consistently prescribed treatment as recommended. Cited barriers include uncertainty about effectiveness beyond 48 hours of symptom onset, concerns about adverse effects, and inconsistent awareness of guidelines among prescribers.^1,3

Clinical and Pharmacy Implications

“After one of the most severe influenza seasons in the past 2 decades, these findings reinforce the importance of treating children with influenza who are hospitalized,” senior author Suchitra Rao, MBBS, MSCS, infectious disease specialist at Children’s Hospital Colorado, said in a news release. “Our findings show that oseltamivir treatment can decrease the risk of needing critical care, even if started beyond the first 2 days of the start of the illness.”²

The American Academy of Pediatrics, CDC, and Infectious Diseases Society of America all recommend antiviral treatment for children hospitalized with suspected or confirmed influenza, regardless of symptom duration. Oral oseltamivir remains the recommended antiviral for hospitalized pediatric patients, dosed twice daily and approved for infants as young as 14 days old. For pharmacists, the results reinforce a role in flagging treatment gaps at admission, supporting timely order verification, and counseling care teams that delayed presentation should not preclude oseltamivir initiation.^4,5

This large, multistate cohort study strengthens the evidence base supporting current guidelines and may help reverse the recent decline in pediatric antiviral use, the study authors noted.¹

REFERENCES

1. Rytlewski K, Dunn A, O'Halloran A, et al. Effectiveness of oseltamivir in hospitalized children with laboratory-confirmed influenza, 2014-2023. JAMA Pediatr. doi:10.1001/jamapediatrics.2026.3376

2. Largest real-world study finds early flu antiviral treatment reduces ICU admissions in hospitalized children. News release. EurekAlert. August 10, 2026. Accessed August 13, 2026. https://www.eurekalert.org/news-releases/1139445

3. Underutilization of flu antivirals. Centers for Disease Control and Prevention. Updated March 20, 2026. Accessed August 13, 2026. https://www.cdc.gov/flu/whats-new/2025-2026-underutilization-of-flu-antivirals.html

4. Recommendations for prevention and control of influenza in children, 2025-2026: policy statement. American Academy of Pediatrics. Pediatrics. 2025;156(6):e2025073620. doi:10.1542/peds.2025-073620

5. Influenza antiviral medications: summary for clinicians. Centers for Disease Control and Prevention. Updated March 10, 2026. Accessed August 13, 2026. https://www.cdc.gov/flu/hcp/antivirals/summary-clinicians.html