It's still around, infecting people in Asia and set to cause another bout of worry-inducing headlines in Europe this winter. There are several strains of avian influenza, but the one that had everyone reaching for their drug stockpiles earlier this year was H5N1. You'd be forgiven for thinking this strain had appeared out of the ether; but it has been around since 1996, when 18 poultry workers were infected in Hong Kong.
The authorities cracked down by slaughtering Hong Kong's entire poultry flock, a tactic that seemed to stop the virus in its tracks. But China had problems with H5N1 in 2003 and, since then, it has been spreading through south-east Asia. This year it arrived in Turkey, killing several people, and eventually turned up in a dead swan in Britain in April. Cue weeks of paranoia.
But the terrifying pandemic never happened, and there are three reasons why. First, H5N1 hasn't shown any signs of mutating so that it can transmit between humans. Second, we emerged from the flu season, at least in Europe. Third, birds are not migrating at the moment. "It has bubbled away all summer in Indonesia," says Mike Skinner, a virologist at Imperial College London. "Their total mortality is the highest of all the countries."
According to the World Health Organisation, 293 people worldwide have been infected by H5N1 so far, leading to 148 deaths. Around 50 cases have been reported in the past few months.
Scientists have been racing to develop better flu treatments. The Medical Research Council put up £10m last December for researchers to look at how H5N1 might mutate and how we could fight it. Drug companies have also been busy creating antiviral drugs and working out how to make vaccines. GlaxoSmithKline announced in June that it could stimulate immunity to flu using smaller amounts of vaccine, which could make stocks go further. Merck is looking at faster ways of creating vaccines - at the moment, they are made using hens' eggs.
But there's little doubt among experts that H5N1 will return this winter. "We'll see more outbreaks - it's almost inevitable," says Skinner.
