Single dose of baloxavir lowers the risk of influenza virus transmission to close contacts: NEJM

A new study published in The New England Journal of Medicine showed that a single dosage of the antiviral baloxavir marboxil (Xofluza) reduced the rate of influenza virus transmission to household contacts.

Because baloxavir marboxil (baloxavir) quickly decreases influenza virus shedding, it may also lessen transmission. Neuramaminidase inhibitor therapy studies have not provided enough proof that they stop transmission to contacts. The use of baloxavir in practical public health strategies is limited by the lack of data regarding its efficacy, effectiveness, appropriate dose administration, or duration of use for the treatment or post-exposure prophylaxis of novel influenza A viruses of pandemic potential, including the highly pathogenic avian influenza A (H5N1) virus. In order to fill the gap in the literature, Arnold Monto and team carried out this investigation.

Within 48 hours of the initial symptoms, individuals aged 5 to 64 with an influenza-positive index were randomized 1:1 to receive either baloxavir or a placebo. By day five, the main outcome was the spread of influenza virus from an index patient to a household contact. By day five, the first secondary end goal was the spread of the influenza virus, which caused symptoms.

As a whole, 1,457 index patients and 2,681 household contacts were included during the 2019–2024 influenza seasons. Nearly, 726 index patients were randomized to the baloxavir group, and 731 to the placebo group. With an adjusted relative risk reduction of 29%, baloxavir significantly reduced the transmission of laboratory-confirmed influenza by day 5 when compared to placebo.

Although the difference was not statistically significant, the adjusted incidence of influenza virus transmission by day 5 that caused symptoms was 5.8% with baloxavir and 7.6% with placebo. During the follow-up period, 7.2% of the index patients in the baloxavir group developed drug-resistant viruses; no resistant viruses were found in household contacts. There were no new warning signs found.

Overall, compared to placebo, treatment with a single oral dosage of baloxavir resulted in a decreased rate of influenza virus transmission to close contacts. Across age categories, seasons, influenza types (A[H1N1pdm09], A[H3N2], and B), durations between symptom start and baloxavir or placebo administration, and geographical locations, there was a difference in the transmission incidence favoring baloxavir. 

Source:

Monto, A. S., Kuhlbusch, K., Bernasconi, C., Cao, B., Cohen, H. A., Graham, E., Hurt, A. C., Katugampola, L., Kamezawa, T., Lauring, A. S., McLean, B., Takazono, T., Widmer, A., Wildum, S., & Cowling, B. J. (2025). Efficacy of baloxavir treatment in preventing transmission of influenza. The New England Journal of Medicine, 392(16), 1582–1593. https://doi.org/10.1056/nejmoa2413156