If the virus does come back as an autumn monster, good social distancing might buy time until vaccines can be made.
"On average you had 70 per cent protection if you had flu in spring," she says. If the current virus, in its apparently mild form, continues to spread, the same could happen this time round. But while infection now may protect some people later, it is still not a good idea to catch it as even the current H1N1 strain can be deadly. However, the fact that the spring virus in 1918 conferred immunity to the deadlier later version bodes well for the efficacy of a swine flu vaccine.
SHOOT: The WHO has recently said a pandemic will infect about 2 billion people. So we might run a little bit short of vaccines.
The 1918 flu started with a mild wave in March, followed by a deadly second wave later in the year. For the 2009 virus to follow the same path, two things need to happen: the virus has to spread readily enough in humans that it does not fizzle out, and it needs to mutate to a nastier form capable of killing more people.
It seems unlikely that this virus will simply fizzle out, as it has already managed to persist for months. Mike Worobey of the University of Arizona at Tucson has analysed the genetic divergence of virus samples from different cases to estimate their most recent common ancestor, a minimum estimate of when the virus jumped to people. He says that it probably appeared sometime between June and November last year, and at the end of November at the latest.
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