Prompt Steps Could Contain Potential Flu Pandemic

NEW YORK (Reuters Health) - The outbreak of bird flu in Asia has prompted fears that the virus might mutate into a form that could be easily passed from person to person, leading to a lethal pandemic. However, researchers say, a global outbreak is not inevitable.

If rigorous surveillance can quickly identify an outbreak of potentially pandemic influenza virus, it is possible that mass preventative treatment and social isolation measures could contain the emerging strain at its source, according to a simulation computer model reported in the research journal Nature.

A similar model, described in Sciencexpress, suggests that prevaccination would make these strategies even more effective, even if the vaccine provided only low to moderate protection.

Both reports are published online August 3rd.

"Modeling helps people plan for an outbreak," Dr. M. Elizabeth Halloran, co-author of the Sciencexpress paper, told Reuters Health. "You can't wait until an outbreak happens. You need international collaboration to have a lot of things already organized ... because you don't know where it's going to occur or how it's going to occur."

The two models simulate outbreaks in Southeast Asia, the focus of the ongoing H5N1 bird flu epidemic.

The one developed by Dr. Neil M. Ferguson and his team represents disease spread among the 85 million people residing in Thailand and in bordering countries, while the model population reported by Halloran and her associates involves 500,000 rural inhabitants of Thailand.

According to Ferguson, at Imperial College London, and his team, provision of preventative treatment with the antiviral drug Tamiflu would probably be inadequate if restricted to social contacts of flu victims.

They suggest that geographic targeting would be more successful, where the whole population within 5 to 10 km of identified cases would be treated, requiring availability of at least 3 million drug courses.

Closure of schools and workplaces and restriction of movements in and out of affected areas would also enhance containment.

Even if containment was unsuccessful, Dr. Ferguson's group says, delaying the widescale spread by a month or more could provide "a potentially critical window of opportunity for accelerating vaccine production."

Meanwhile, Halloran, who is based at Emory University in Atlanta, said her group's research yielded similar conclusions. Their results suggest that deployment of 120,000 courses of Tamiflu within 2 to 3 weeks of detection in a restricted rural region would contain the pandemic.

They also looked at the benefits derived from human influenza H5N1 vaccine currently in development, but which is likely to be poorly matched to any emerging strain.

According to their model, "by having even a low-efficacy prevaccination in place with just 50 percent coverage helped the other interventions to be more effective," she said.

SOURCE: Nature 2005 and Sciencexpress 2005.