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Baloxavir marboxil (Xofluza) may be more effective than oseltamivir (Tamiflu) in preventing household flu transmission, according to new research from Japan.

In a simulated model using an insurance claims database, the proportion of families with a secondary influenza infection was estimated to be twice as high if index cases received oseltamivir rather than baloxavir marboxil (19.35% vs 9.57%, respectively), reported Takahiro Takazono, MD, of the Nagasaki University Hospital in Japan, and colleagues.

Regardless of influenza viral type, a multivariate analysis showed a median odds ratio (2.5th and 97.5th percentiles) of 1.73 (1.68-1.77), suggesting more intrafamilial transmission with oseltamivir, the authors wrote in .

Subgroup analyses looking at month of onset and age of the index patient showed similar results.

"Although influenza symptoms are self-limiting and can subside within a week in most patients, the infection can result in severe illness or death in high-risk patients," the group noted. "Because most secondary infections are acquired from a household member, curbing intrafamilial infections is a key goal of influenza prevention globally."

In the U.S., baloxavir marboxil, a selective cap-dependent endonuclease inhibitor, is FDA approved to treat acute uncomplicated influenza in symptomatic people ages 12 and up, and as post-exposure prophylaxis as well. In severe flu cases, prior research has shown that adding baloxavir marboxil to neuraminidase inhibitors such as oseltamivir did not result in any significant clinical improvement.

For their study, Takazono and colleagues examined JMDC claims data on 146,676 families from the 2018-2019 flu season where an index case had received baloxavir marboxil (n=84,672) or oseltamivir (n=62,004).

Researchers simulated flu infection durations of index cases using a "based on antigen-specific virus shedding periods." Inclusion required that families had health insurance. Index cases requiring hospitalization in the first 2 days of receiving treatment were excluded.

The study's primary endpoint was the proportion of families with intrafamilial flu infections.

Index cases receiving baloxavir marboxil tended to be older than the oseltamivir group, where two-thirds were under age 12. Overall, most of the index cases were infected with influenza type A (71%) versus type B (0.9%), with the remaining being unknown.

The authors acknowledged several limitations to their study, including the use of non-confirmed "shared family codes," which may not reflect the actual number of household members living together. Transmission involving non-household settings, such as those occurring in schools or other centers, were not assessed.

Additionally, it is possible that family members of index cases could have had pre-existing infections prior to the treatment of index cases, they noted. Lastly, only a single flu season with few type B infections was evaluated.

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