Covid-19 prevention: The most important variable in reopening schools

Many schools across the US gambled on offering in-person classes in early August, even as their states were still battling uncontrolled spread of Covid-19.

In some of those schools, it hasn’t gone well.

In Georgia’s Cherokee County School District, for example, there have been at least 80 positive cases since August 3, and more than 1,100 students, teachers, and staff have had to quarantine. At the high school in Paulding County School District, which came to national attention after photos of halls crowded with mostly maskless students went viral, several students and staff have tested positive, forcing the school to adopt a hybrid model of in-person and virtual learning. In Atlanta, one second-grader tested positive the day after classes started; the same week, a seven-year-old with no underlying conditions died from the virus.

Scientists have found clear evidence that children, especially those over 12, can and do transmit the virus, though the disease is generally more mild than in adults. This means school outbreaks can be a risk for students, teachers, and the wider community.

While many school districts that reopened are reporting infected students, these initial cases may not have originated in the classroom. “For most of these cases in Georgia, schools weren’t open long enough for the transmission to be coming from within the schools,” says Megan Ranney, an emergency physician and the director for the Center for Digital Health at Brown University, who researches pediatric mental health.

Nevertheless, infected students and staff arriving in the first week of school have already prompted shutdowns and quarantines around the country; in Mississippi, over half of counties have reported Covid-19 cases in teachers, staff, or students.

What’s remarkable is that health experts predicted that cases among young people would surge if schools reopened before community transmission was under control — yet many school districts went ahead anyway. “This is exactly what we’ve been warning about — when you have high levels of Covid in the community, you will have cases showing up in schools, just because people are catching it out in the community,” says Ranney.

And it’s not just kids, teachers, and parents who are then at risk — school outbreaks can fan wider outbreaks in communities. A recent superspreading event in Ohio, for example, found that children between ages 6 and 16 were part of the chain of transmission, passing the virus on to other children and adults.

A third grade teacher sits in an empty classroom as she talks with her students over video on the second day of class at Richman Elementary School in Fullerton, California, on August 12.
Jeff Gritchen/MediaNews Group/Orange County Register via Getty Images

The World Health Organization recommends that schools open only if fewer than five percent of those tested for the virus over a two-week period are positive. In the US, the cut-off for what is considered “safe” for reopening schools currently varies by state, but they all tend to look at similar factors: Oregon, for example, has said counties must have fewer than 10 cases per 100,000 people for three weeks before in-person classes resume. Arizona calls for less than 100 cases per 100,000, or a two-week decline in cases, as well as meeting other standards like hospital capacity.

For comparison, Georgia has had 2,236 cases per 100,000 people in the last seven days as of August 16. (You can check your own state’s rates at the Centers for Disease Control and Prevention here.) In Georgia, many schools also reopened despite high positivity rates — the percentage of people being tested for Covid-19 who have a positive result. Georgia’s number of positive tests per 100,000 people were also well above the general threshold that public health experts recommend for in-person activities.

A recent study from the American Academy of Pediatrics and the Children’s Hospital Association found that 97,000 children in the US got Covid-19 in the last two weeks of July— representing a 40 percent increase, or almost one-third of the total number of pediatric cases since the pandemic began. It’s unclear whether this is an increase in actual infections, or if more children, who are often asymptomatic, are now being tested as schools reopen.

Since testing overall is still inadequate to control the virus in the US, the CDC says the true incidence of Covid-19 in children is still unknown. But as Tom Frieden, former director of the CDC recently tweeted, kids between 5 and 17 now have the highest positivity rate of all age groups. “Age groups aren’t an island,” he wrote. “Spread in any group is a risk to all.”

The US Department of Education is not publicly tracking Covid-19 cases in K-12 schools, numbers of students quarantined, deaths, or school closures. That led a Kansas teacher to create a crowdsourced Google spreadsheet using media reports to track positive cases of Covid-19 associated with schools in over 40 states. It shows that more than 2,000 students, faculty, administrators and staff have tested positive for Covid-19 nationwide since early July, and that teachers have already died in Mississippi, Alabama, and California.

Public health experts at the University of Texas at Austin recently published a report analyzing the likelihood that students and teachers would arrive on the first day of school already infected. They found it largely depends on the size of the school, and how prevalent Covid-19 is in that school’s community. Based on data from mid-July, their model suggests that in Texas, a school of 100 individuals in Denton County could expect one to two Covid-19 cases in the first week, while higher rates in Harris County likely make up four cases.

Hidalgo County, which currently has a 17 percent positive test rate, looks worse yet, with two to eight cases predicted. (Racial and economic disparities contribute to these differences; Hidalgo County is 90 percent Latinx and has seen a disproportionate number of Covid-19 cases.) These numbers are constantly changing — but they show that with high enough levels of community transmission, you can pretty much guarantee that at least one person will go to school infected, potentially exposing others.

In other countries where data on school-linked outbreaks is more readily available, the impacts of reopening schools have been mixed. In Denmark, reopening schools for 2- to 12-year-olds didn’t make the country’s already minimal outbreak worse. But many precautions were taken to limit transmission.

Denmark reopened elementary schools with extensive safety measures in place, like staggered entry time. Students were placed in small groups to reduce interaction, and hotels and libraries were utilized as additional class space. Even still, the rate of infection increased after Danish schools reopened, although not enough to keep total cases from declining.

In Israel, new cases have skyrocketed since schools reopened two months ago— but the country also lifted other distancing measures at the same time, making it harder to tease apart the causes. There are many factors that can make reopening schools safer, like mask-wearing, social distancing, and regular testing, so it’s difficult to directly compare different countries’ school plans.

Still, there’s a definite trend: Countries like Vietnam and New Zealand, which have generally done a good job controlling spread, have successfully reopened schools. Others, with higher community transmission, like Chile, have struggled.

With a new disease, it’s important to look at the totality of the emerging body of research on different age groups, rather than individual study results. For example, a widely cited South Korean study initially reported in July found that adolescents might actually spread the virus more than adults; an update from the same researchers this week found that some of the teens’ purported transmission was likely due to families actually sharing outside exposure.

Overall, the sum of evidence — including independent studies from the US, Iceland, and Germany — finds older children may be as likely to spread the virus as adults when infected. A recent literature review found that “opening secondary/high schools is likely to contribute to the spread of SARS-CoV-2.” (The same review found that children under age 10 may be less susceptible to infection.)

Another review published in The Lancet highlights that adequate testing and contact tracing are essential to reopening schools. That’s not possible currently in many US states, which are still seeing positivity rates as high as 23 percent, along with extreme delays in test results.

Chethan Sathya, a pediatric surgeon and assistant professor of surgery at the Cohen Children’s Medical Center in New York, says that people seem to be missing the point that having an incomplete picture of how Covid-19 impacts kids is not license to send them back to school to find out. Ranney points out that some states, like New York and her home state of Rhode Island, currently have low test positivity, and so it may be safer to reopen schools in those areas. ”The only possible road to reopening schools is with low rates of community transmission,” she says.

“Emerging data suggests that it’s unsafe to send children and teachers into school buildings, even with safety protocols, if the prevalence of cases in the community is too high,” she says. If schools choose to reopen anyway, she adds, “it’s an ongoing experiment on children and staff.”

Lois Parshley is a freelance investigative journalist. Follow her Covid-19 reporting on Twitter @loisparshley.

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