March 2, 2006
Study: Containment strategy may only delay bird flu
Containing an emerging bird flu pandemic at its source is likely to only delay, and not stop, the spread of illness. That’s because pathogens are likely to be introduced not just once but several times, say researchers from the UW and the Harvard School of Public Health.
“If a single introduction of a pandemic-capable strain is likely to happen, then multiple introductions are also likely,” said Mark Lipsitch, associate professor of epidemiology at Harvard. “If there are multiple introductions, then there are numerous chances for containment, and the strategy only has to fail once to result in a pandemic.”
Lipsitch and Carl Bergstrom, a UW assistant professor of biology, are co-authors of a paper describing new computer modeling of a bird flu pandemic published last week in the online edition of the open-access journal PLoS Medicine (PLoS stands for Public Library of Science). The lead author is Christina Mills, an epidemiology doctoral student at Harvard.
“We wanted to answer a basic question: If avian influenza emerges once, what are the chances it will emerge more than once,” Bergstrom said.
The researchers assumed there would be multiple introductions of pandemic flu strains and concluded that containment strategies could at best gain time before an inevitable pandemic.
“From the point of view of policy planning, we should not give up on containment, but embed it within a multi-pronged plan that includes vaccine development, improved surveillance, and risk reduction measures, such as limiting human-to-bird contact — particularly after the first containment effort,” Mills said.
Containment describes attempts to reach a pandemic source as early as possible and then apply public health tools such as vaccination, antiviral drugs, and quarantine to curb a pathogen’s spread. Containment is one component of federal planning for a possible flu pandemic, and is the centerpiece for World Health Organization efforts.
But World Health Organization spokeswoman Maria Cheng acknowledged to the Canadian press last week that the paper’s claim is likely valid. She said that while her organization is pursuing a containment strategy, it also is warning that such a strategy could fail. It could, however, buy time to allow nations to make more preparations and to let companies produce more vaccine, she said.
The researchers argue that resources would be strained with each new effort at containment, making subsequent control strategies more and more difficult to implement. Under good circumstances, containment efforts may only double the time before a pandemic emerges, the researchers have calculated. That time could drop even further if efforts underpinning the containment, such as surveillance for human cases, are inadequate.
Bergstrom suggested that the emphasis be shifted from containment and towards strategies such as collecting sick birds or developing vaccines, though he said that does not mean giving up on containment totally.
“We just want to suggest that people shouldn’t put all their eggs in the containment basket,” he said.
The work is part of the Models of Infectious Disease Agent Study, supported by the National Institute of General Medical Sciences of the National Institutes of Health.
