Simulations of response in U.S., Britain based on travel, population data

By Tim Parsons
School of Public Health

Using complex computer models, a team of researchers analyzed how effective travel restrictions, school closures, drug distribution and other public health strategies would be in slowing the spread of a pandemic flu outbreak. The analysis, conducted by researchers at the Johns Hopkins Bloomberg School of Public Health, Imperial College London and RTI International, simulated a response to a pandemic flu outbreak in the United States and Great Britain using detailed population data and travel patterns. It is published in the April 26 online edition of Nature.

"The modeling shows that there is no single magic bullet which can control a flu pandemic. However, a combination of interventions could be highly effective at reducing transmission, potentially saving lives," said Neil M. Ferguson, lead author of the study and professor at Imperial College London.

According to the simulation, the pandemic would peak about 60 to 80 days after the first case is reported. Closing off the borders and restricting travel within the country were unlikely to delay the spread of the flu for more than two to three weeks, unless these measures were more than 99 percent effective. Nationwide school closures could reduce the peak infection rate by 40 percent but would do little to reduce the overall number of people infected. However, slowing the peak rate could ease the burden on the health care system, according to the researchers. Quarantining sick individuals at home, if feasible, was also found to have a significant impact on the number of people infected.

Combining measures could reduce the number of cases further. Antiviral drug distribution, in conjunction with school closures, could reduce the number of cases by 50 percent if the medications were used to treat those who live with sick individuals as well as those already ill. The researchers said more widespread preventive drug treatment could reduce infection rates by 75 percent, but such treatment would be difficult to accomplish.

To have an impact on infection rates, vaccines would need to be available within two months of an outbreak, which is much faster than current vaccine manufacturing technology allows. However, a stockpile of vaccine for at least 20 percent of the population could reduce the number of infections by one-third, even if the vaccine would provide only limited immunity. Vaccinating children first, since they are the biggest spreaders of influenza, had the greatest impact on transmission rates, while vaccinating seniors first had the least.

"Computer models are becoming powerful tools for exploring the potential outcomes of interventions to mitigate the spread of pandemic flu," said Jeremy M. Berg, director of the National Institute of General Medical Sciences, which partially funded the study through its Models of Infectious Disease Agent Study, or MIDAS. "The results of simulations using these models can be useful for planning ways to prepare for and respond to a future outbreak," he said.

Donald S. Burke, professor in the Bloomberg School's Department of International Health and director of the school's MIDAS program, said, "By using simulated epidemics 'in silicon,' we think through and evaluate response strategies before the event happens."

Johns Hopkins authors on the study, "Strategies for Mitigating an Influenza Pandemic," are Derek A.T. Cummings and Burke.

Funding was provided by the National Institute of General Medical Sciences MIDAS Program, the Medical Research Council, the Royal Society and the Howard Hughes Medical Institute.

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