Scientists have worked out how the seasonal flu virus has become resistant to the anti-influenza drug Tamiflu and why these drug-resistant strains have spread explosively in the past two years.
The H1N1 seasonal flu virus first became resistant to Tamiflu more than 10 years ago because of a single genetic mutation. But these strains were unable to spread because the same mutation that conferred resistance to Tamiflu also made the virus less infectious.
However, the researchers have discovered further genetic mutations that overcame this drawback to the drug-resistant strain. These mutations allowed the virus to spread explosively after the 2007-08 flu season so that by the following year, Tamiflu was next to useless against virtually all seasonal H1N1 flu viruses – although still effective against other flu viruses .
