Flu Drug Blocks Household Spread by 86%

By Gene Emery

July 09, 2020

(Reuters Health) - A single dose of the influenza drug baloxavir marboxil, if given quickly to the family members of someone who has developed the flu, can prevent 86% of parents and siblings from falling ill themselves, according to a new Japanese study published in the New England Journal of Medicine.

"The trial adds baloxavir to other antiviral agents . . . that have shown efficacy in reducing the transmission of influenza virus in households when used for early treatment in index patients and for postexposure prophylaxis in their contacts," according to an accompanying editorial by Dr. Timothy Uyeki of the U.S. Centers for Disease Control and Prevention in Atlanta.

Other such drugs are oseltamivir, zanamivir and peramivir. Baloxavir is sold under the brand name Xofluza by Roche. Shionogi, which developed the drug and has marketing rights in Japan, paid for the study.

The test, conducted during the 2018-2019 influenza season, involved giving the drug or placebo to 752 volunteers who lived in the household of someone - frequently a child - who had just been diagnosed with influenza, usually influenza A.

Among placebo recipients, 13.6% developed the flu themselves. But among those who took a baloxavir pill instead, only 1.9% fell ill (P<0.001).

"A single oral dose of baloxavir was highly effective in preventing influenza in household contacts," said the research team, led by Dr. Hideyuki Ikematsu of Ricerca Clinica in Fukuoka, Japan.

"Baloxavir prophylaxis was effective in high-risk participants, in children younger than 12 years of age, and in unvaccinated participants," they said.

The household members getting the drug, 19% of whom were under the age of 12, were just as likely to experience side effects as those who took a placebo.

Dr. Uyeki noted that the drug is currently not approved in the U.S. for children under 12. But in Japan, younger children are typically given an antiviral agent if they develop the flu.

When the Ikematsu team looked at the results for those younger children given the drug, they found that it lowered the risk of illness by 73%.

Another factor that could affect its benefits in the U.S., said Dr. Uyeki, is that "unlike in Japan, where patients typically seek medical care for influenza testing and early antiviral treatment soon after the onset of illness, in the United States, even high-risk patients with influenza may not present within 2 days after the onset of illness and may not always receive early antiviral treatment."

The drug has to be given early to be most effective.

There is concern that the flu virus might develop a resistance to baloxavir, which was approved in the U.S. and Japan in 2018.

The Ikematsu team said the new results "suggest the need for studying its prophylactic efficacy in other non-household settings," such as dormitories and schools.

SOURCES: https://bit.ly/2BU1Gbc and https://bit.ly/3gDOaHv The New England Journal of Medicine, online July 8, 2020.