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Flu is a slippery customer. The virus constantly alters its surface proteins so that we can be infected many times over a lifetime and a vaccine made last year no longer works. Now it appears this behaviour is just a decoy to guard the virus's more vulnerable parts – a fact that might able us to make drugs, or a vaccine, that will work on all kinds of flu, year after year. Flu's main surface protein, haemagglutinin, looks like a lollipop. Our immune systems mostly produce antibodies to its rounded head, and it is this part that changes every year, making immunity short-lived. But in a large library of human antibodies, Wayne Marasco at Harvard University and colleagues found very few that bind its "stalk", which barely changes at all, either through time or between different flu viruses.

To see if this might provide a way to attack the virus, they produced large amounts of the antibodies that home in on the stalk and found that they cured and protected mice from two kinds of H5N1 bird flu, as well as many other flu families including H1N1 pandemic and ordinary flu. The researchers now want to develop the antibodies as a flu drug, possibly to stockpile for pandemics. The team also plans to test the stalk antibody as a vaccine, so that people produce more of these antibodies themselves. They suspect haemagglutinin's big head is a decoy aimed to attract the immune system's attention and to stop us making many antibodies to the stalk – a delicate bit of molecular machinery that not be so easy to change to evade our immune attacks. In tests on mice, they found that the flu viruses did not evolve to escape the treatment. Another benefit is that such antibodies stay effective for more than three weeks when injected into people, and in a pandemic could keep people alive long enough to produce their own antibodies to the virus.

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