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A widely predicted bird flu pandemic, which experts say could kill millions of people, could be avoided if health authorities act fast to control the initial outbreak, say two teams of researchers.

The outbreak would have to be detected within 48 hours, warns one team. The other says that people affected, as well as those in their immediate surroundings, would need to receive flu drugs within 21 days. Giving people a vaccine, even one that does not exactly match the pandemic virus, would also help, they say.

Bird flu is caused by the H5N1 virus. It affects poultry but has also killed 55 people in South-East Asia since December 2003. Health experts fear it could mutate into a form that spreads from person to person, causing a pandemic that would cost millions of lives (see Time to prepare for bird flu pandemic 'running out').

Keeping the pandemic in check will depend on being ready to detect and respond to the new form of virus, say the researchers.

The predictions come from two separate research teams whose findings are published online on 3 August by the journals Nature and Science.

Both teams created computer models of an H5N1 outbreak in Thailand.

They simulated different strategies for controlling the outbreak, using varying combinations of drugs, vaccines, and quarantine methods to determine the best way to prevent the virus from spreading.

"Our findings indicate that we have reason to be somewhat hopeful," says Elizabeth Halloran of Emory University, United States, who co-authored the Science paper.

"If — or, more likely, when — an outbreak occurs in humans, there is a chance of containing it and preventing a pandemic," she says. "However, it will require a serious effort, with major planning and coordination, and there is no guarantee of success."

Halloran's team simulated a rural population of 500,000 people, taking into account how they travel and come into contact with each other, for example at work or school.

The difficulty of containing an outbreak will be partly determined by how infectious the virus is — in other words how many people someone with the disease will pass it on to.

So far, the bird flu virus is only mildly infectious to people, and no cases of human-to-human transmission have been confirmed by the World Health Organization (WHO).

But experts fear that the virus will change with time to become more infectious.

The researchers found that the outbreak could be contained if someone with bird flu passed it on to an average of 1.4 others, and if health authorities delivered anti-flu drugs to people surrounding the outbreak within 21 days.

If health authorities were to vaccinate half the population before the outbreak, even with a vaccine that is not perfectly matched to the pandemic virus, then drugs would be able to contain an outbreak if each infected person passed the virus on to 1.7 others on average.

But if the virus were more infectious, infected people and their households would need to be quarantined to guarantee containment.

Halloran's team concluded that the WHO's stockpile of anti-flu drugs "could be sufficient to contain a pandemic" if it were deployed at the source of the emerging pandemic within two to three weeks of detection.

The authors of the second study, published in Nature, agree that health authorities need to adopt a combination of measures to contain an outbreak.

Led by Neil Ferguson of Imperial College, United Kingdom, they simulated a population of 85 million living in Thailand and bordering regions of neighbouring countries.

Ferguson's team underlines the importance of detecting the outbreak early. "Rapid, sensitive case detection and delivery of treatment to targeted groups, preferably within 48 hours of a case arising" is key, write the authors, adding: "surveillance is perhaps the single greatest challenge."

In a statement released today, the WHO said: "If we have a chance to reduce the scale of a pandemic with [antiviral drugs] and other public health measures, the success of these interventions will depend on effective disease surveillance and early reporting in risk-prone countries." 

"In a lot of countries that have experienced bird flu, the warning is a challenge," a WHO spokesperson told SciDev.Net, comparing stockpiling drugs without building an adequate surveillance network to building a new fire station without installing fire alarms.

Link to full paper in Nature

Link to full paper in Science

Nature doi:10.1038/nature04017
Science doi: 10.1126/science.1115717


Click here for an example of an uncontrolled outbreak of avian flu. Red represents areas with infected individuals, and green represents areas which have recovered from infection. [AVI format - 65Mb]

Click here for an example of a controlled outbreak of avian flu. Red indicates areas of infection while blue indicates areas where a combination of control measures has been implemented. [AVI format - 17Mb]

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