Following Swine Flu Online

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Others say that tracking the spread of the virus could help reveal how deadly it is, how easily it spreads, whether drug resistance is emerging, and how to target precious public-health resources. Jeffrey Herrmann, an applied mathematician and software engineer at the University of Maryland, has developed software that can analyze the spread of a disease and pinpoint the best locations for treatment or mass vaccination. He says that this approach "could be used by local public-health departments to determine how many sites and how many staff they need to dispense antiviral medication or vaccinate people."

The WHO's Pandemic Influenza Task Force decided on Monday to raise the alert to level 4 on the pandemic scale. This means that confirmed human-to-human transmissions are now causing community-level outbreaks.

"We might expect up to 30 percent to 40 percent of the population to become ill in the next six months," says Neil Ferguson, a member of the WHO task force and a professor of epidemiology at Imperial College London. He adds that the virus appears less lethal than H5N1 bird flu--but crucially, it's more contagious. In the six years since its emergence in 1993, H5N1 has killed 257 people; swine flu has already killed 150 in a matter of weeks. The last pandemic, Hong Kong flu, killed about 700,000 (1 in 1,000 of its victims) in 1968.

So far, no deaths have been reported outside of Mexico, but the consensus among virologists is that it is too early to say whether suggestions that the death rate is higher in Mexico will be borne out. Some have suggested that better treatment in the United States has made infections there less dangerous. Or it could be that the much greater number of cases seen so far in Mexico--there are now more than 2,000 suspected--has made some deaths there more likely.

Pharmaceutical firms, meanwhile, have begun the race to produce a vaccine. Switzerland's Novartis said on Tuesday that it had received the genetic code of the new virus strain, enabling it to begin work in earnest. The WHO estimates that an effective inoculation is still six months away, but this might be in time for a second wave of infection later in the year.

Peter Dunnill, a professor of biochemical engineering at University College London, warns that even if a vaccine is produced, not everyone will have access to it. "Based on calculations done in relation to H5N1, the global capacity for providing a vaccine at its most optimistic is less than 10 percent of the world's people," he says.

Antiviral drugs are likely to provide the first line of defense. In the United States, Homeland Security Secretary Janet Napolitano said recently that she will release a quarter of the 50 million courses of antiviral drugs in the national stockpile. She added that the Defense Department has another 7 million courses ready. But their effectiveness could be short lived--particularly if they are used now, and the virus resurfaces later in the year. Professor of immunology Peter Lachmann of the University of Cambridge says, "Tamiflu resistance is extraordinarily widespread and develops very quickly. We would be very lucky if this virus does not develop resistance."