Timely interventions such as closing schools and workplaces, along with antiviral drugs, should be able to significantly slow the spread of an influenza pandemic through a large city, U.S. researchers said Monday.

They looked at three computer simulation models to determine how such a pandemic might travel through a city similar in size to Chicago.

"All of the simulations suggest that the combination of providing pre-emptive household antiviral treatments and minimizing contact could play a major role in reducing the spread of illness," they said in a study published in the Proceedings of the National Academy of Sciences.

The combined intervention strategies tested by the computer-modelling groups, if done early in an outbreak, were found to reduce the number of secondary influenza cases by as much as 80 per cent, said researcher Stephen Eubank of Virginia Tech in Blacksburg, Va.

Besides limiting contacts at work and school, other "social distancing" measures used in the models included voluntary quarantine and travel restrictions.

Members of the virtual community interacted the way people normally do: within households, schools and workplaces, and the community at large. All three models were set up to have attack-rate patterns similar to those of past U.S. flu pandemics.

"The good news was that all three of the disease-modelling groups involved in the study found that an outbreak of pandemic flu similar to the pandemic of 1918 could be mitigated if these measures were implemented quickly," said leader author M. Elizabeth Halloran.

Use of a vaccine was not factored into the study. Eubank told the Reuters news agency that limits on social contacts, therefore, would be expected to last for weeks if not months, until a vaccine can be manufactured.

Eubank said news of an influenza pandemic would prompt people to limit their contacts with others regardless of what civic planners decide, so he thinks a large segment of the population would not have a problem with such stringent measures.