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Students at a University of London class in Mexico City wear masks to protect them against swine flu in May 2009. High schools and universities closed by the pandemic had just reopened across Mexico. (AP)

When Flu Pandemics Hit, Closing Schools Can Slow Spread

Feb 9, 2012 — When schools in Alberta, Canada, closed for summer in 2009, it put the breaks on the swine flu outbreak in the province, says research from McMaster University. But authorities have to weigh the costs and benefits of preemptive closure, and there isn't always a clear answer.

Everyone knows that when your kids get the flu, they stay home from school.

But what does it take to justify closing the school down entirely? That's a question we should probably answer before the next big pandemic hits.

At one point during the swine flu outbreak in 2009, the Centers for Disease Control and Prevention said, "The potential benefits of preemptively dismissing students from school are often outweighed by negative consequences," such as disruption of classes and hassles for parents.

But a study of swine flu transmission in Alberta, Canada, published this week in Annals of Internal Medicine, lends weight to the benefits of school closure. Researchers compared rates of new diagnoses of swine flu from the beginning of the pandemic, in April 2009, through summer vacation and into the following school year.

"When schools closed [for summer], there was a huge reduction in the amount of transmission among school-age children," David Earn, professor of mathematics at McMaster University and lead author of the study, tells Shots.

But that's not all. The end of the school year caused a big drop in transmission among other age groups, too. Earn says rates for all ages dropped by at least 50 percent, and "probably a lot more than that." School children, in other words, were a major driver of flu transmission to the entire population.

Earn says summer vacation kept the pandemic manageable until a vaccine was produced, which took until October 2009. There was still a spike in flu cases that fall, but having kids out of school for two months "bought enough time that the vaccine was ready before a lot of people became infected," he says.

His team also used a computer simulation to model what would have happened if schools had remained in session all summer. It predicted a slight drop in transmission due to seasonal effects of temperature and humidity, but would have left a lot more people infected — essentially giving the virus a running start into the autumn flu season.

In the U.S., the CDC took a cautious approach at the start of the outbreak, recommending that any school with a confirmed case of swine flu close for up to 14 days. Within a week it relaxed that guidance, saying local authorities should weigh the benefits of preventing new illnesses against the costs of school closures.

By the end of the pandemic, in Aug. 2010, only a handful of the nearly 100,000 elementary and secondary schools in the U.S. had closed because of swine flu.

The CDC's guidelines for the current flu season don't say much about closures, instead saying schools should "focus on early identification of ill students and staff, staying home when ill, and good cough and hand hygiene etiquette."

Earn says that makes sense. "Nobody's thinking about closing schools during a normal flu season," he says. But "if you're faced with a pandemic in the future...then closing schools for a long period may be worth it."

In an email, a CDC representative said the agency is studying the impact flu-related closures had on families, and is working on updated guidance for schools.

But in the event of another pandemic, she wrote, "Any decisions would be based on the individual characteristics of the pandemic (severity, how it's dispersed, etc) and the latest scientific evidence of the time regarding benefits of school closure."

Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.