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Baloxavir Shows Greatest Viral Clearance Among Three Oral Influenza Antivirals in Head-to-Head Trial
In a randomised controlled trial of 944 adults with early seasonal influenza, baloxavir accelerated oropharyngeal viral RNA clearance by 86% compared with no treatment (95% CrI 60–117), outperforming both favipiravir at 66% (95% CrI 45–94) and oseltamivir at 49% (95% CrI 28–74), though none of the three agents meaningfully shortened the time to complete symptom resolution.
What Was Studied
The trial investigated the relative antiviral efficacy of three oral influenza therapies — baloxavir marboxil, favipiravir, and oseltamivir — never previously compared simultaneously in a single controlled study. The primary measure was the rate of oropharyngeal influenza viral RNA clearance over five days, assessed using daily quantitative PCR and modelled with a Bayesian hierarchical framework.
How It Was Studied
AD ASTRA was a phase 2, open-label, adaptive, randomised platform trial enrolling 944 adults aged 18–60 years with acute symptomatic seasonal influenza of no more than four days’ duration and a low risk of progression to severe disease. Participants were recruited across hospital outpatient and primary care settings in Thailand, Laos, Nepal, and Brazil. Patients were assigned in equal proportions to baloxavir (single dose, weight-adjusted), favipiravir (loading regimen followed by twice-daily dosing for four days), oseltamivir (75 mg twice daily for five days), or no study drug, with randomisation stratified by site. The modified intention-to-treat population comprised those with PCR-confirmed influenza and a baseline viral density exceeding 250 RNA copies per mL, totalling 729 patients across the four primary arms.
What Was Observed
- Baloxavir produced the fastest viral clearance, accelerating the rate by approximately 86% relative to no treatment (95% CrI 60–117). The posterior probability that the increase exceeded 20% was 1.0, meeting the prespecified superiority threshold with high certainty.
- Favipiravir and oseltamivir also significantly accelerated viral clearance compared with no treatment — favipiravir by roughly 66% (95% CrI 45–94) and oseltamivir by about 49% (95% CrI 28–74) — with both likewise achieving a posterior superiority probability of 1.0.
- Oseltamivir was inferior to baloxavir in head-to-head comparison, clearing virus approximately 20% more slowly (95% CrI 6–32), with a posterior probability of 0.93 that the reduction exceeded 10% — formally establishing inferiority. Favipiravir was 10% slower than baloxavir (95% CrI −4 to 22), but non-inferiority could not be confirmed (posterior probability only 0.55).
- Fever resolved faster with all three antivirals compared with no treatment, with absolute differences in median time to fever resolution ranging from 0.5 to 0.9 days. However, time to resolution of all symptoms was not significantly different across any of the groups, and the safety profile was broadly comparable, with only five severe adverse events recorded across the entire trial.
Why This Matters
This is the first trial to simultaneously compare baloxavir, favipiravir, and oseltamivir within a single adaptive platform, generating a direct efficacy hierarchy using a pharmacometric viral clearance endpoint. The authors propose that this approach can inform prioritisation of antiviral agents for further clinical development and for inclusion in pandemic preparedness stockpiles, where choices among available oral antivirals must be made under uncertainty.
How to Read This Result
This well-designed, multinational randomised trial provides robust virological evidence favouring baloxavir, but the open-label design may have introduced bias in subjective outcomes, and the inability to establish favipiravir’s non-inferiority to baloxavir leaves its relative standing uncertain.
Limitations
The open-label design is a meaningful source of potential performance and assessment bias, particularly for patient-reported endpoints such as symptom resolution. Enrolment was restricted to adults aged 18–60 years at low risk of severe disease, which limits applicability to older, immunocompromised, or high-risk populations where antiviral choices are most consequential. The absence of a significant difference in time to complete symptom resolution across groups raises questions about whether the observed virological gains translate into clinically meaningful benefit. Finally, the non-inferiority of favipiravir relative to baloxavir was not established, leaving the two agents’ relationship inconclusive.