Influenza A(H1N1) Virus was first observed in Mexico in 2009 and managed to become pandemic in a matter of months. A vaccine was quickly developed and now you simply have to get your yearly jab to be safe from a potentially life-threatening infection.
But, like I said so many times before, the virus manages to evade a vaccine time and time again. So, what if you end up in hospital as a result of a somewhat mutated virus? Doctors starts treating you with Neuraminidase Inhibiting (NAI) antiviral drugs like oseltamivir (Tamiflu) and zanamivir (Relenza), because the Influenza A(H1N1)pdm09 Virus has remained conveniently susceptible to these NAIs.
We have seen a few worrisome clusters of NAI resistant flu, which have raised concerns that we could one day see a an antiviral resistance in our current H1N1 strain. That day seems to have arrived, because scientists founds an elevated number of NAI resistant viruses with 'permissive mutations' circulating in Japan and describes the discovery of resistant pH1N1 carrying a G147R substitution that conferred resistance to both oseltamivir and peramivir.
The first widespread community cluster of the H275Y mutant A(H1N1)pdm09 virus was detected in Newcastle (Australia) in 2011. The H275Y substitution in the NA protein would destabilize the mutant virus. However, two additional V241I and N369K substitutions in the NA of H275Y mutant viruses were reported to increase their replication and transmission fitness, contributing to efficient transmission.
Almost all recently circulating A(H1N1)pdm09 viruses possess these permissive substitutions, suggesting an increased risk for H275Y mutant viruses to emerge and spread globally.
 E Takashita et al: Influenza A(H1N1)pdm09 virus exhibiting enhanced cross-resistance to oseltamivir and peramivir due to a dual H275Y/G147R substitution in Eurosurveillance - 2016
 Hurt et al: Characteristics of a widespread community cluster of H275Y oseltamivir-resistant A(H1N1)pdm09 influenza in Australia in Journal of Infectious Diseases – 2012