Charlottesville, VA—With the prospect of the COVID-19 pandemic continuing into the annual influenza season this fall and winter, a new study on controlling household transmission has special significance.

The report in the New England Journal of Medicine advises that a single dose of the flu drug baloxavir marboxil can reduce the spread of the illness within households.

A team including researchers from the University of Virginia School of Medicine, Japanese researchers, and other colleagues focused on 752 household contacts of 545 patients with the flu found that transmission was much less common in household members who received the drug compared to those who received a placebo. 

In fact, the authors write, only 1.9% of uninfected household contacts who took a single dose of baloxavir marboxil, marketed as Xofluza, got sick with influenza versus 13.6% of those who received the placebo.

“This trial established that baloxavir, if taken within a day or so after exposure, is highly effective for preventing influenza illness in households, a high-risk setting for virus transmission,” explained coauthor Frederick G. Hayden, MD, of the University of Virginia School of Medicine. “The findings indicate that baloxavir prophylaxis should prove effective for prevention in other circumstances, such as outbreaks in nursing homes and healthcare facilities, although formal studies will need to be undertaken.”

Baloxavir is a polymerase acidic protein (PA) endonuclease inhibitor with clinical efficacy in the treatment of uncomplicated influenza, including in outpatients at increased risk for complications, according to the study, which notes that the postexposure prophylactic efficacy of baloxavir in the household setting has been unclear.

To provide some answers, researchers conducted the multicenter, double-blind, randomized, placebo-controlled trial to evaluate the postexposure prophylactic efficacy of baloxavir in household contacts of index patients with confirmed influenza during the 2018–2019 season in Japan. With a primary end point being clinical influenza confirmed with testing, participants were assigned in a 1:1 ratio to receive either a single dose of baloxavir or placebo.

Of the index patients, 95.6% had influenza A virus infection, 73.6% were younger than 12 years of age, and 52.7% received baloxavir. 

Based on the results, the authors conclude, “Baloxavir was effective in high-risk, pediatric, and unvaccinated subgroups of participants. The risk of influenza infection, regardless of symptoms, was lower with baloxavir than with placebo (adjusted risk ratio, 0.43; 95% CI, 0.32 -0.58).”

The study also determined that the incidence of adverse events was similar in the two groups—22.2% in the baloxavir group and 20.5% in the placebo group.

Background information in the report notes that households and other close-contact settings such as dormitories and schools are important sites for seasonal and pandemic transmission of influenza virus. Researchers recount that previous household-based randomized, controlled trials have shown that postexposure antiviral prophylaxis with adamantanes, when circulating viruses were susceptible, or neuraminidase inhibitors is effective in reducing the risk of influenza among contacts. When rimantadine was used both for the treatment of the household index case and for postexposure prophylaxis, however, “drug-resistant influenza A virus emerged rapidly and was transmitted to contacts, causing prophylaxis failure,” they add.

Transmission of resistant virus was not observed when either oral oseltamivir or inhaled zanamivir was used for both treatment and prophylaxis within households, according to the report.

Baloxavir marboxil (baloxavir) was approved as a single-dose treatment for uncomplicated influenza A and B in Japan and the U.S. in 2018 and was recently approved in the U.S. for the treatment of influenza in patients who were at risk for complications. FDA approval was based on studies showing that baloxavir treatment within 2 days after the onset of illness shortened the duration of illness by approximately 1 day compared with placebo and showed superior antiviral efficacy to both placebo and oseltamivir.
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