Single-dose baloxavir linked to reduced influenza transmission

1. In this randomized controlled trial, influenza-positive patients who received a single dose of baloxavir had a 29% lower adjusted risk of transmitting influenza to household contacts by day five compared to placebo.

2. Symptomatic transmission was also lower with baloxavir, but the difference was not statistically significant.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Influenza is a highly contagious respiratory virus that spreads rapidly, particularly within households. Baloxavir marboxil is a single-dose antiviral that inhibits viral replication by targeting the influenza virus cap-dependent endonuclease. This large, multicountry, phase 3b randomized controlled trial evaluated whether treating influenza-positive individuals with baloxavir reduces transmission to household contacts. Index patients aged 5–64 received either baloxavir or placebo within 48 hours of symptom onset. Among 2681 household contacts, lab-confirmed transmission by day five was significantly lower in the baloxavir group compared to placebo. The study was well-powered, methodologically rigorous, and showed consistent trends across subgroups. However, the study’s generalizability may be limited due to the high percentage of unvaccinated participants. The clinical benefit regarding symptomatic transmission was not statistically significant, possibly due to lower than expected incidence. No major safety concerns emerged, though 7.2% of baloxavir-treated patients developed drug-resistant mutations, none of which were transmitted. Overall, this trial supports baloxavir’s potential role in influenza transmission reduction.

Click to read the study in NEJM

Relevant Reading: Inhaled Zanamivir for the Prevention of Influenza in Families

In-Depth [randomized controlled trial]: This phase 3b double-blind, randomized controlled trial assessed the efficacy of single-dose baloxavir marboxil in preventing household transmission of influenza. Conducted from 2019 to 2024 across 15 countries, the study enrolled 1,457 influenza-positive index patients (ages 5–64) within 48 hours of symptom onset and randomized them 1:1 to receive either baloxavir or placebo. A total of 2,681 household contacts were enrolled, with 2,216 meeting criteria for the primary analysis population (unvaccinated, influenza PCR–negative at baseline, and linked to an influenza-positive index case). The primary endpoint was laboratory-confirmed transmission of the influenza virus (same type/subtype) to a household contact by day five. Transmission occurred in 9.5% of household contacts in the baloxavir group versus 13.4% in the placebo group, yielding an adjusted odds ratio of 0.68 (95.38% confidence interval [CI], 0.50 to 0.93; P = 0.01). This corresponds to a 29% adjusted relative risk reduction (95.38% CI, 12% to 45%). The first secondary endpoint—symptomatic influenza transmission by day five—occurred in 5.8% of contacts in the baloxavir group versus 7.6% in the placebo group (adjusted odds ratio, 0.75; 95.38% CI, 0.50 to 1.12; P = 0.16), which did not reach statistical significance. By day nine, overall influenza infection (regardless of symptoms) was also lower in the baloxavir group (14.0%) compared to placebo (18.7%), with an adjusted odds ratio of 0.71 (95% CI, 0.54 to 0.94). This trial provides evidence that baloxavir reduces influenza transmission within households and supports its use not only for treatment but also as a transmission-reducing intervention during seasonal epidemics or pandemics.

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