Can Tamiflu save us from bird flu? (Part II)

“Last month the WHO reported that a patient in Vietnam was infected with a strain of H5N1 resistant to Tamiflu”

Tamiflu can save lives if it is given early, no more than two days after symptoms first appear. But last month the WHO reported that a patient in Vietnam had a strain of H5N1 resistant to Tamiflu. So could the drug become useless before the pandemic even begins?

Luckily the resistant viruses may be poor at spreading, according to Fred Hayden of the University of Virginia, a leading expert on antiviral therapy. The mutation that made the Vietnam virus drug resistant also occurs in a normal human flu strain, making the virus a hundred times less contagious. In Japan, which uses Tamiflu for ordinary flu epidemics, the mutation appears in 16 per cent of treated children, yet such viruses almost never go on to infect others.

It is probable that the same will be true of any drug-resistant strains of H5N1. This assumption needs to be tested as soon as possible, Hayden says.

But even if Tamiflu remains effective in most cases, it might not be enough to stop a pandemic. The real difficulty with the WHO's antiviral plan, Hayden says, will be finding and treating all the cases and contacts in time. "But that doesn't mean we shouldn't try," he adds.

Ira Longini of Emory University in Atlanta, Georgia, says much depends on how fast the virus spreads. If each infected person passes the virus to fewer than two other people on average, then isolating and treating all cases and their contacts with antivirals could slow or even stop an epidemic, he calculates.

But health workers would not be able to keep up with the virus if sick people infect between two and three others, as happened in the 1918 flu pandemic. Drug stockpiles would still help save lives, Longini says, but would not halt the outbreak.

The best chance of the antiviral strategy succeeding will be in the early stages, when the virus might still spread slowly. The trouble, however, is that most stockpiles of Tamiflu are being acquired by rich countries in Europe and North America, not poor countries such as Vietnam, where any H5N1 pandemic is most likely to start.

What's more, Tamiflu is in short supply. Seventeen countries have ordered stockpiles of the drug from the Swiss company Roche, which holds the patent, and 10 more are said to be discussing purchases. The UK's order for 14.6 million five-day courses of treatment will take two years to fulfil, for instance. The drug is made from a plant in limited supply, and Roche is still trying to develop methods for synthesising it from scratch.

There are two other drugs that target the same enzyme as Tamiflu. But zanamivir (Relenza) must be taken by inhalation and is not widely available, while peramivir was dropped by US company Johnson & Johnson, which thought it unlikely to be profitable. BioCryst, the small Alabama firm that created peramivir, is still trying to find a new partner.

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