Positive Phase III study results have shown that preventive flu treatment with baloxavir marboxil (Xofluza, Genentech and Roche) after exposure to an infected household member reduced the risk of contraction by 86% versus a placebo, according to Roche.

Roche's Baloxavir marboxil is the first and currently only single dose oral medication approved to treat influenza in otherwise healthy patients, according to the company. Clinical evidence has demonstrated the benefit of baloxavir marboxil in several populations including those at higher risk for contraction, as well as in several treatment settings.

The BLOCKSTONE study found that just 1.9% of Xofluza-treated household members contracted the flu, as opposed to 13.6% in the placebo-treated group. This benefit remained statistically significant regardless of the influenza A subtype.

Baloxavir marboxil is the first in a new class of antiviral medications designed to inhibit the CAP-dependent endonuclease protein, which is necessary for viral replication. While it is FDA-approved for the treatment of acute, uncomplicated influenza in patients 12 and older, a Supplemental New Drug Application is currently under review by the FDA for a single-dose treatment for people at high risk of complications from the flu.

Because of the significant threat of seasonal epidemics, the ability of the virus to spread quickly from person to person is an important piece of treating the virus. Seasonal epidemics result in up to 650,000 deaths each year, so limiting the spread of infection is critical.

The Phase III, randomized, post-exposure prophylaxis study evaluated a single dose of Xofluza compared with the placebo as a preventive treatment specifically for household members living with someone with influenza. The primary endpoint was to evaluate the proportion of participants who tested positive for the influenza virus and had a fever, as well as one or more respiratory symptoms between days one and ten. Secondary endpoints included clinical efficacy, pharmacokinetics, safety, and tolerability.

The researchers also found the same benefit in household contact that are considered at high risk of flu-associated complications and children under 12 years old.

No serious adverse events were reported for baloxavir marboxil, which had a similar safety profile to the placebo. The overall incidence of adverse events was 22.2% for baloxavir marboxil and 20.5% for the placebo.

In addition, the study found that even when fewer criteria for flu were applied—fever or respiratory symptoms, as opposed to both, there was still a statistically significant reduction in the risk of household members contracting the virus.


Positive phase III results show Xofluza reduces risk of developing flu after contact with an infected person by 86% [news release]. Basel, Switzerland; September 2, 2019: Roche website. https://www.roche.com/media/releases/med-cor-2019-09-02b.htm. Accessed September 6, 2019.