Oseltamivir Reduces ICU Admission in Hospitalized Children With Flu

Children hospitalized with laboratory-confirmed influenza who received oseltamivir had a significantly lower hazard of intensive care unit (ICU) admission and a shorter hospital length of stay (LOS) compared with untreated children, according to a cohort study published in JAMA Pediatrics.¹

The study drew on 8 influenza seasons of data from the Influenza Hospitalization Surveillance Network (FluSurv-NET), a CDC-supported, population-based surveillance system spanning 13 states. Researchers called the analysis one of the most comprehensive real-world evaluations of antiviral treatment in pediatric influenza to date.²

Study Design and Key Findings

The retrospective cohort study included children younger than 18 years hospitalized with laboratory-confirmed influenza across the 2014-2015 through 2022-2023 seasons, excluding 2020-2021 because of low case volume during the COVID-19 pandemic. After exclusions, 6044 cases were included in the primary ICU analysis, of whom 4240 (70.2%) received oseltamivir, and 7103 cases were included in the secondary LOS analysis, of whom 5746 (80.9%) received oseltamivir.¹

Using time-dependent oseltamivir exposure anchored at respiratory symptom onset, the researchers found that treatment reduced the hazard of ICU admission (adjusted hazard ratio [aHR], 0.69; 95% CI, 0.60-0.80) and increased the hazard of hospital discharge, meaning a shorter LOS (aHR, 1.13; 95% CI, 1.06-1.21), compared with no treatment. The estimated LOS was 3.72 days for untreated patients versus 3.33 days for treated patients, a 9.4-hour reduction associated with oseltamivir.¹

Notably, both early treatment (2 days or less from symptom onset) and late treatment (3 days or more from symptom onset) were associated with a decreased hazard of ICU admission compared with no treatment (aHR, 0.74; 95% CI, 0.63-0.86, and aHR, 0.55; 95% CI, 0.41-0.73, respectively), and the effect persisted even when treatment began more than 5 days after symptom onset.¹

“After one of the most severe influenza seasons in the past two decades, these findings reinforce the importance of treating children with influenza who are hospitalized. Our findings show that oseltamivir treatment can decrease the risk of needing critical care, even if started beyond the first two days of the start of the illness,” Suchitra Rao, MD, professor in the department of pediatrics at the University of Colorado Anschutz School of Medicine, said in a news release.²

Antiviral Use in Decline Despite Guideline Support

The study's authors noted that use of antivirals for hospitalized pediatric patients with laboratory-confirmed influenza has been declining nationally. According to FluSurv-NET data cited in the study, only 63% of children hospitalized with influenza received antivirals during the 2024-2025 season, down from 86% in the 2017-2018 season.¹

National organizations, including the CDC, Infectious Diseases Society of America, and American Academy of Pediatrics, recommend antiviral treatment for all pediatric patients hospitalized with suspected or confirmed influenza, regardless of symptom duration. The study authors pointed to adverse effect concerns, doubts about effectiveness, and limitations in earlier observational research as likely contributors to the treatment decline.¹

Unlike prior studies that relied on administrative diagnosis codes and did not account for antiviral use before hospitalization, this study anchored treatment timing to respiratory symptom onset and used laboratory-confirmed cases, which the authors said helped address misclassification bias and immortal time bias present in earlier research.¹

What This Means for Pharmacists

Oseltamivir (Tamiflu) is a neuraminidase inhibitor that works by blocking the influenza virus enzyme responsible for viral replication and spread.³ The drug is rapidly absorbed after oral administration and converted primarily by hepatic esterases to its active metabolite, oseltamivir carboxylate.⁴

For treatment of influenza, standard dosing in adults and adolescents is 75 mg twice daily for 5 days, and pediatric dosing for children 1 year and older is weight-based, typically ranging from 30 to 75 mg twice daily for 5 days.³

Pharmacists counseling caregivers should note that oseltamivir works best when started within 2 days of symptom onset and that the full 5-day course should be completed even if symptoms improve early to reduce the risk of symptom recurrence. The oral suspension should be shaken well before use and measured with the dosing dispenser provided rather than a household teaspoon.³

Common adverse effects include nausea, vomiting, and abdominal pain, and pharmacists should counsel caregivers to seek immediate care for signs of serious allergic reaction or unusual behavioral changes, such as agitation or irritability, which have been reported primarily in children and adolescents.³

Dosage adjustment is recommended in patients with reduced renal function, and the drug should not be given within 2 weeks before or 48 hours after the live intranasal influenza vaccine.³

The new JAMA Pediatrics findings may prompt renewed pharmacist engagement in encouraging timely antiviral initiation for hospitalized pediatric patients, given the observed benefit even when treatment started beyond the traditional 48-hour window.¹

Conclusion

The study authors concluded that oseltamivir treatment significantly reduced the likelihood of ICU admission and decreased hospital LOS among children hospitalized with laboratory-confirmed influenza, supporting current national recommendations to treat all hospitalized pediatric influenza patients with oseltamivir as soon as possible, regardless of time from symptom onset or underlying risk factors.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. Published online August 10, 2026. doi:10.1001/jamapediatrics.2026.3376

2. University of Colorado Anschutz. Largest real-world study finds early flu antiviral treatment reduces ICU admissions in hospitalized children. News release. EurekAlert!. August 10, 2026. Accessed August 11, 2026. https://www.eurekalert.org/news-releases/1139445

3. Oseltamivir (oral route) - side effects & dosage. Mayo Clinic. Accessed August 11, 2026. https://www.mayoclinic.org/drugs-supplements/oseltamivir-oral-route/description/drg-20067586

4. McClellan K, Perry CM. Oseltamivir: a review of its use in influenza. Drugs. 2001;61(2):263-283. doi:10.2165/00003495-200161020-00011