A groundbreaking international study has demonstrated that a single dose of baloxavir marboxil (Xofluza) can significantly reduce the transmission of influenza within households, potentially transforming approaches to both seasonal and pandemic influenza management.
The phase 3b CENTERSTONE trial, published in The New England Journal of Medicine, found that treating influenza-infected individuals with baloxavir reduced the odds of virus transmission to untreated household members by 32% compared to placebo. This represents the first robust evidence that an antiviral treatment can effectively limit the spread of influenza to close contacts.
Trial Design and Key Findings
The double-blind, randomized, placebo-controlled study enrolled 1,457 influenza-positive index patients and 2,681 household contacts across 15 countries from 2019 to 2024. Index patients aged 5 to 64 years received either baloxavir or placebo within 48 hours of symptom onset.
The primary endpoint measured laboratory-confirmed influenza transmission to household contacts by day 5. Results showed the adjusted incidence of transmission was 9.5% in the baloxavir group compared to 13.4% with placebo (adjusted odds ratio = 0.68 [95.38% CI: 0.50–0.93]; p=0.013).
For the key secondary endpoint of symptomatic influenza transmission, baloxavir showed a clinically meaningful 25% reduction in transmission resulting in symptoms (5.8% vs. 7.6%), though this difference did not reach statistical significance (p=0.16).
"These results highlight baloxavir's potential not only to treat influenza but also to reduce its spread within communities," said Professor Benjamin Cowling, co-author of the study and Helen and Francis Zimmern Professor in Population Health at the University of Hong Kong. "This dual effect could transform how we manage seasonal influenza and prepare for future pandemics."
Viral Dynamics and Safety Profile
The study revealed that baloxavir led to a faster reduction in viral titers compared to placebo. By day 3, baloxavir-treated patients showed a mean reduction of 2.22 log₁₀ TCID₅₀/mL versus 1.85 log₁₀ TCID₅₀/mL for the placebo group.
While drug-resistant viruses emerged in 7.2% of baloxavir-treated index patients, these resistant strains were not detected in household contacts, suggesting limited transmission risk.
The safety profile remained consistent with previous studies, with adverse events reported in 4.6% of baloxavir-treated patients compared to 7.0% in the placebo group. No new safety concerns were identified.
Public Health Implications
Approximately one-third of all influenza virus transmission occurs within households, making this setting crucial for intervention strategies. The findings from CENTERSTONE could have significant implications for reducing community-wide spread.
"This trial is the first to demonstrate an antiviral effect that reduces transmission of influenza viruses within a household. This result may potentially have broad-reaching implications for public health," said Dr. Levi Garraway, Chief Medical Officer and Head of Global Product Development at Roche, which markets baloxavir as Xofluza.
The results underscore the complementary role of antiviral drugs alongside vaccination, particularly in unvaccinated populations or during pandemics when vaccines may not be immediately available.
Global Influenza Burden
Seasonal influenza infects an estimated one billion people worldwide annually, causing millions of hospitalizations and up to 650,000 deaths globally. The economic impact is also substantial, with up to 75% of working adults experiencing approximately two days of absenteeism due to influenza, whether they or someone within their household is sick.
With multiple respiratory viruses now co-circulating throughout the year, including COVID-19, effective options to treat and prevent the spread of influenza are increasingly important for public health systems.
Regulatory Status
Results from the CENTERSTONE trial have been submitted to health authorities, including the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA). Baloxavir is currently approved in more than 75 countries for the treatment of uncomplicated influenza types A and B, and in several countries as a preventative treatment (post-exposure prophylaxis).
The CENTERSTONE trial was funded by F. Hoffmann-La Roche and the U.S. Department of Health and Human Services, Administration for Strategic Preparedness and Response, Biomedical Advanced Research and Development Authority.
