With the rapid rise of coronavirus cases in the U.S., a number of schools across the country are considering closing to prevent the spread of the virus.

However, there are few reports of children getting sick with the virus or developing serious symptoms, even as cases worldwide reach nearly 100,000. So does it make sense to close schools, given that children seem to be largely spared from the worst impacts of the virus?

The answer is not a simple one. It's true schools can serve as ideal places for germs to spread. But previous studies on whether school closures could prevent the spread of another novel respiratory virus — pandemic flu in 2009 — had mixed results. Some suggested a benefit only under certain circumstances, such as if schools remained closed for very long periods.

What's more, schools must weigh any potential benefit of closures with a slew of other factors, such as whether parents will be able to take time off work, whether children who depend on school meals will have adequate food at home, and exactly how long the facility should be closed, experts say.

"It's not an easy decision to make, and it's not clear that it will be helpful," said Dr. Amesh Adalja, an infectious disease expert at the Johns Hopkins Center for Health Security in Baltimore.

Why close schools?

Some experts say schools should not be closed for COVID-19, the name of the disease caused by the new coronavirus, unless there is active transmission in the community.

"Just like with the flu, we would not close the school unless we know that there is a lot of transmission going on in the community," said Krys Johnson, an epidemiologist at the Temple University College of Public Health. "I think that should still be our marker here."

In this case, the reason for closing schools has less to do with preventing the spread of coronavirus among children (who aren't hit hard by the virus), and more to do with preventing the spread to parents, grandparents, teachers and adult staff, who may be at risk for more serious infections, Johnson said.

Indeed,  schools and day care centers can be breeding grounds for respiratory illnesses and other infections. "Kids are pretty good vectors of most things… because they are touching and curious just by nature," Johnson told Live Science. The idea is that closing schools prevents the spread to the wider community.

Unanswered questions 

However, most of the scientific data on the effects of school closures comes from studying influenza, Adalja said. Some of these studies do suggest a benefit — for example, a 2008 study in the journal Nature suggested that school closures during an influenza pandemic in France may reduce the total number of cases by up to 17%. However, children are major spreaders of the flu, but it's unclear if the same is true for the new coronavirus. The World Health Organization's report on a mission to China found children made up just 2.4% of coronavirus cases.

"The impact [of school closures] may be less with coronavirus," Adalja said.

However, another survey, in Shenzhen, China, found that during later stages of the outbreak, 13% of coronavirus cases were in children. That suggests that children could be important players in spreading SARS-CoV-2 after all.

But even if children are major contributors to the spread of this virus, there may not be a benefit to school closures if officials wait until the virus is already widespread in the community. "If you already have intense transmission in your community, it's not going to serve a purpose" to keep kids home, Adalja said. In other words, if everyone is already sick, it won't affect the trajectory of the outbreak, he said.

A 2007 study of the 1918 pandemic flu in the U.S., published in the journal JAMA, found that school closures and bans on public gatherings at the city level were tied to lower death rates from the flu, particularly if these measures were implemented early on in the outbreak.

There's also the question of how long to keep kids home. A 2010 study that used computer simulations to explore the effects of closing schools during the 2009 flu pandemic in Pennsylvania found that school closures need to last throughout most of the epidemic — which ended up being about 8 weeks for the 2009 pandemic flu — to have a significant effect. For coronavirus, we don't know what duration of school closure would be effective. What's more, in the 2010 study, short school closures appeared to make the outbreak worse by bringing susceptible kids back into school in the middle of an epidemic, according to the study, published in the Journal of Public Health Management & Practice. .

For now, the Centers for Disease Control and Prevention recommends that schools work with local health departments to determine whether to close when there is active transmission of COVID-19 in the community. The agency notes that guidance on the topic may change as more information becomes available.

Decisions on whether to close schools should be "informed by the best science," Adalja said. "Local health departments may be the best source of that."