【卫报】The science: Is swine flu as deadly as we think?

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The science: Is swine flu as deadly as we think?
http://www.guardian.co.uk/world/2009/may/01/swine-flu-faq

Alok Jha Friday 1 May 2009 22.51 BST

What is the significance of the first person-to-person transmission of the H1N1 virus?

This is the point at which the virus could, theoretically, start to spread exponentially through the population. But it has been taken into account already by officials; because the new H1N1 virus has already jumped the species barrier into humans, scientists knew the bug would become transmissible between humans at some stage.

Dr Mark Fielder, a medical microbiologist at Kingston University, says it should not be a major cause for concern. "It's a fairly mild disease really. Its ability to spread between people, while there, is not enormous."

He adds that maintaining good standards of hygiene and following the Health Protection Agency's advice about regular handwashing and sneezing into tissues would halt the ability of the virus to spread quickly.

"The one thing to recognise is that we haven't had that many deaths yet. We've had far more deaths from other diseases going on in the world than we have had from this form of influenza. I really don't see it becoming a major mortality event. I see a number of people getting ill, but I'll hazard it will be no greater than normal seasonal flu."

Have the deaths in Mexico been hyped?

Robert Booy, head of clinical research at the National Centre for Immunisation Research and Surveillance based at the University of Sydney, believes there is a simple explanation for the concentration of more than 100 deaths in Mexico. "It's likely that this outbreak has been running for not one month or even six weeks, but more than eight weeks [in Mexico]. Influenza tends to, on average, infect two people for every one case. The doubling then occurs every three days, which is the serial interval. This means that from day one to day 30 you go to about 1,000 cases, but in the next month, you go to a million."

This means that, if there have been hundreds of thousands of cases already in Mexico, then about 100 deaths gives a mortality rate of 0.1%.

"So the disease may not be nearly as severe as people thought," says Booy. "If the disease has been around for two months and infected so many people, many of them must be mildly infected and we haven't heard about them."

Again, this shows that H1N1 is, at the moment, not as lethal as most people might think.

What are scientists doing now?

Samples of the H1N1 virus arrived at the National Institute for Medical Research in north London this week and scientists there will now grow the virus structure and see how it might evolve. Working with the Centres for Disease Control and Prevention in Atlanta, Georgia, the research will help develop a vaccine for the virus in the coming months.