Strategies may include stockpiling early vaccines based on guessed flu strains, developing a system for quickly producing and distributing a tailor-made vaccine, and possibly restricting social mobility, scientists at the Los Alamos National Laboratory and the University of Washington said on Monday.

The findings were published in an online edition of the National Academy of Sciences.

Relying on antiviral drugs alone to combat a pandemic would require a large stockpile of medication, noted the researchers.

In the United States, over 10 million courses of antiviral drugs are needed, simulations results suggested, along with either extensive planning or on-the-spot decisionmaking for efficient distribution.

For highly transmissible flu virus strains, the demand for antivirals would likely exceed any reasonable supply, the researchers said.

A quick-response vaccination would be the most effective single strategy, according to the researchers, but uncertainties about exact future virus strains make it impossible to stockpile well-matched vaccines.

Instead, a vaccine from potential strains could be used to control the pandemic until well-matched vaccines are quickly produced and distributed, the researchers said.

Additionally, closing schools or restricting travel in affected areas might be necessary to slow the spread of a highly transmissible virus strain until vaccines could be distributed, they said.

"Based on the present work... we believe that a large stockpileof avian influenza-based vaccine containing potential pandemic influenza antigens, coupled with the capacity to rapidly make a better-matched vaccine based on human strains, would be the best strategy to mitigate pandemic influenza," the researchers wrote in the paper.

The large-scale simulation model examines the spread of a pandemic influenza virus strain, such as an evolved, human-to-human transmissible H5N1 bird flu virus, in the United States. It runs on the Los Alamos supercomputer that has 2,048 processors.

The simulation rolls out a city- and census-tract-level pictureof the spread of infection through a synthetic population of 281 million people over the course of 180 days, and examines the impact of interventions, from antiviral therapy to school closures and travel restrictions, as the vaccine industry struggles to catch up with the evolving virus.

"It's probably not going to be practical to contain a potential pandemic by merely trying to limit contact between people (such asby travel restrictions, quarantine or even closing schools), but we find that these measures are useful in buying time to produce and distribute sufficient quantities of vaccine and antiviral drugs," said Germann, the lead author of the study at the Los Alamos Laboratory.

"Based on our results, combinations of mitigation strategies such as stockpiling vaccines or antiviral agents, along with social distancing measures could be particularly effective in slowing pandemic flu spread in the U.S.," added Ira Longini, a co-author of the study.