CHICAGO (Reuters) - Closing schools during an influenza pandemic could prevent one in seven cases of flu, British researchers said on Wednesday in a study that suggests such action would have less impact than some other estimates.
But they said school closings would create significant hardships for working parents, who might be forced to create informal daycare arrangements that would undo efforts to contain the spread of flu.
"We find school closings would be less effective than some studies have suggested," said Dr. Simon Cauchemez of Imperial College London, whose study appears in the journal Nature.
"The main effect would be to slow and flatten the outbreak -- so the numbers becoming ill in the worst week of the outbreak might be reduced by up to 40 percent, reducing peak demand on health-care systems," Cauchemez said in an e-mail.
Health experts almost universally agree that a global epidemic -- a pandemic -- of influenza is overdue. The most likely cause now is H5N1 avian influenza, which could evolve into a form that passes easily from person to person.
Government estimates suggest vaccines and drugs will not be enough to slow or prevent a flu pandemic. The U.S. pandemic plan recommends closing schools and implementing strategies to limit social contact as a way to limit transmission.
If done quickly, such widespread measures combined with drugs and vaccines might reduce transmission in a large city by as much as 80 percent, by one estimate.
But such estimates are often based on widely varying assumptions, Cauchemez said. He and colleagues instead used public health data from France that compared flu transmission when school was in session and during school holidays.
They found school holidays prevent 16 to 18 percent of seasonal influenza cases. When extrapolated to a pandemic, they said prolonged school closure might reduce the cumulative number of cases by 13 to 17 percent, and peak attack rates by 39 to 45 percent.
But that impact would be reduced if it proved too difficult to keep children apart. "If we want the policy to have an impact, children must be kept relatively isolated and not cared for in groups," Cauchemez said.
U.S. cities that quickly closed schools and discouraged public gatherings during the great flu pandemic of 1918 -- which killed tens of millions of people globally -- had as many as 50 percent fewer deaths than cities that took less decisive measures, according to a recent study.
Cauchemez said an especially deadly pandemic might provide strong incentives for people to keep their children at home. "It might nonetheless be difficult for a lot of working parents to be absent from their work for months to look after their kids," he said.
Cauchemez said a prolonged outbreak might force working parents to put their children into informal daycare settings, a risk governments need to consider when they formulate pandemic flu plans.
"We can't predict how people will behave, but we need to be aware that if this happens, school closings might have no effect at all on flu transmission," he said.
H5N1 bird flu only rarely infects people now. It has killed 239 out of 379 infected, according to the World Health Organization, but could easily mutate into a form that one person could pass to another, and governments around the world are preparing for the possibility.
Editing by Maggie Fox and Eric Walsh