Tamiflu & Relenza Resistance is a certainty rather than a risk

Two anti-flu drugs are commonly stockpiled for use in a flu pandemic: oseltamivir, which is sold as Tamiflu, and zanamivir, which is sold as Relenza. Both work by inhibiting an enzyme called neuraminidase (the 'N' in H1N1). The virus needs this enzyme to break down normal cell walls and to replicate using a mutated version of the victims own RNA.

The 2 drugs act on different parts of the enzyme and resistance to one drug does not confer resistance to the other. The Mexican H1N1 strain is currently classed as being 'sensitive' to both drugs. This is not a 'cure' it is simply a 'treatment' and no one knows how long this 'sensitivity' will last.

The Wu team conducted their study after noticing that despite concerns about resistance, many countries stockpile just one drug, usually oseltamivir. There are some exceptions, however, including Australia and the UK, which stockpile both drugs.

Viruses are notorious for their ability to develop resistance to drugs. Last year, an H1N1 flu strain that caused some seasonal flu rapidly developed resistance to oseltamivir. By December, "close to 100 per cent of H1N1 in Australia and the US, and many other parts of the world, were resistant to Tamiflu", says Raina MacIntyre, an infectious disease expert at the University of New South Wales in Sydney, Australia.