Antivirals and Resistant Influenza A(H7N9)

As always, the best way to avoid getting the seasonal flu is to get yourself vaccinated. But some variants of Influenza are not (yet) covered by the vaccine. One of those not covered is Influenza A(H7N9), which is currently circulating on mainland China.

If vaccination is not possible, all you can do is hope that you won’t get infected because all sorts of precautions may not be enough if the scattered cases suddenly turn into a full-blown pandemic.

But if you are infected with, say, the Influenza A(H7N9) virus, what can be done to save your life? Well, doctors will administer large doses of antiviral drugs such as oseltimivir (marketed as Tamiflu), zanamivir (marketed as Relenza), laninamivir (marketed in Japan as Inavir) or peramivir (marketed in Japan as Rapiacta). But do not think you’re safe when you are treated with one of those antivirals because at the best of times antivirals may have some effectiveness in preventing the development of infection in people exposed to the influenza virus and antivirals can reduce the duration of symptoms and illness.

The Influenza virus itself however is reacting aggressively and it is rapidly acquiring resistance against these antiviral drugs. This resistance means that the virus has mutated and a mutated virus is often not as virulent as it was before. The virus acquired resistance at the cost of biological fitness and that suggested these novel viruses were unlikely to spread easily and widely.

But the Influenza virus has outsmarted us again and recent research[1] revealed that genetic studies of Influenza A(H7N9) show that it is now completely resistant to the primary anti-flu drug oseltimivir and partially resistant to zanamivir. Despite having the capacity to withstand anti-viral treatment, Influenza A(H7N9) remains virulent and transmissible. One set of mutations imparting resistance has not forced a predicted diminution in other powers of the virus.

[1] Hai et al: Influenza A(H7N9) virus gains neuraminidase inhibitor resistance without loss of in vivo virulence or transmissibility in Nature Communications - 2013