Seasonal Flu Drugs May Protect Against H7N9 Influenza

Tamiflu
A new study finds that human H7N9 influenza strains are sensitive to antiviral drugs used for seasonal flu viruses. Tamiflu by Tony Hisgett | Flic

Some drugs normally used to treat seasonal influenza are also effective against strains of the H7N9 avian influenza ('bird flu') virus that struck East Asia earlier this spring, according to virologists from Wisconsin. Their study, which was published today in the journal Nature, also uncovered reasons for why drug resistance developed for the popular flu antiviral Tamiflu.

Their main goal was to analyze what genetic steps led H7N9 to jump from birds to humans, killing 43 out of 133 confirmed cases.

"H7N9 [avian] viruses have several features typically associated with human influenza viruses and therefore possess pandemic potential and need to be monitored closely," said Dr. Yoshihiro Kawaoka of the University of Wisconsin-Madison and the University of Tokyo, who is one of the world's leading experts on avian flu.

The researchers noted that the adaptation to humans required just a handful of changes in the protein that flu viruses use to pentrate cells — called hemagglutinin or the "H" in H7N9. These mutations likely facilitated the viruses' ability to infect and replicate in humans and mammals in general.

"H7N9 viruses combine several features of pandemic influenza viruses, that is their ability to bind to and replicate in human cells and the ability to transmit via respiratory droplets," said Kawaoka, who demonstrated the latter point by infecting ferrets with H7N9 viruses. Ferrets are a popular model with the study of influenza, especially when scientists are trying to determine if the viruses can spread in the air.

Akin to results from a previous study published in late May, H7N9 was swapped between ferrets via airborne transmission. However, similar to what was seen with human epidemic, aerosol transmission of H7N9 wasn't as efficient as seasonal flu viruses.

In addition, the authors checked whether or not seasonal influenza drugs could protect against H7N9.

Laninamivir, which is approved in Japan but not in the U.S., as well as Tamiflu were marginally effective against H7N9 infection in mice. However, some strains were able to fight off Tamiflu, which could explain why resistance to the drug was also seen in the field.

Excitingly, a new experiemental drug called Favipiravir, which is in Phase II clinical trials for seasonal flu, was nearly twice as beneficial in reducing viral levels compared to Tamiflu and laninamivir.

Scientists are rushing to better understand H7N9 before the flu season arrives, just in case the virus decides to rear its ugly head again. Government officials have called for the development of an H7N9 vaccine, and many candidates are rising to the challenge. A few days ago, the pharmaceutical Inovio reported 100-percent protection for the animals that received its new vaccine, while the Maryland-based Novavax just initiated Phase I clinical trials with its drug.

 

Source: Watanabe T, Kiso M, Fukuyama S, et al. Characterization of H7N9 influenza Aviruses isolated from humans. Nature. 2013.

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