As school officials try to figure out whether to open classrooms this fall, the science they need to make these tough choices is still evolving. A few things are clear: That most kids don’t become as seriously ill from Covid-19 as adults, and have much lower fatality rates. That’s according to data from the US and China published by the Centers for Disease Control.
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But the question of how likely children are to spread it to teachers, staff and other students still hasn’t been settled. One large new study from South Korea found children under the age of 10 appear to not transmit the virus very well. While it's not exactly clear why, the pediatric infectious disease experts contacted by WIRED say that it's perhaps because young children expel less air that contains the virus and are shorter, so any potential respiratory droplets are less likely to reach adults. A study published in April by researchers at the Brigham and Women’s Hospital in Boston suggests that younger kids haven’t developed the molecular keys that the virus exploits to enter the body and wreak havoc on the respiratory system, microscopic structures known as ACE2 receptors.
But older students are more like adults in their ability to transmit the virus, according to the South Korea study, which makes school opening decisions tougher. Should administrators allow only elementary students to attend in person, while middle and high schoolers stay online at home? If they do, will younger children be able to keep their masks on all day or stay six feet apart? What about the psychological effects of continued isolation on teens, who many parents believe are already racking up too much screen time during the pandemic shutdown and now are facing months of online learning?
The CDC announced school reopening guidelines on Thursday that call for officials to reopen classrooms this fall, based on the idea that children do not become as sick from Covid-19 and are less likely to spread it as adults, and to belay any emotional and psychological harm from the disruption of schools staying closed. The agency issued these new guidelines after President Donald Trump attacked initial rules that called for desks being set 6 feet apart, staggered lunches, and temperature screenings, as being too costly and burdensome.
Dimitri Christakis helped draft a separate set of reopening guidelines for US schools in a report for the National Academy of Sciences released July 15. It says schools should take steps to reopen for younger students in grades K-5 and those of all ages who have special needs. Christakis says that with appropriate social distancing, hand-washing and protective masking, the risk to teachers, staff and students in a school can be reduced.
“With those additional precautions, primary school teachers should feel comfortable going to school,” says Christakis, director of the Center for Child Health, Behavior and Development at Seattle Children's Research Institute. “Those are the kids for which in-person learning is so important. We should prioritize these kids.”
At the same time, Christakis admits there are still some unknowns about transmission among school-age children. “We don’t have the answer to what extent children transmit the virus in general, and in particular in a school setting,” he says. “This is called the ‘novel coronavirus’ for good reason. It is acting very differently than most respiratory viruses and many other coronaviruses. Children appear to be less affected directly, and potentially less likely to transmit.”
Physicians like Christakis have been following the publication of epidemiological studies around the world to help make decisions about what might happen when schools might reopen in the US. Some countries, like Norway and Denmark, reopened their schools in the late spring starting with younger students. Schools there boosted sanitizing procedures and limited class size, keeping children in small groups at recess and putting space between desks. With these practices in place, neither country saw a rise in cases after reopening schools in April and May, according to a report on worldwide school practices compiled by the University of Washington Department of Global Health earlier this month.
Other countries, like Israel, opened schools at the same time that restrictions were lifted in May on surrounding communities, which led to Covid-19 outbreaks that had infected 1,335 Israeli students and 691 staff as of July 15. In Israel, schools reopened without masking or social distancing rules, according to The Wall Street Journal, and allowed up to 40 students per class, unlike the Scandanavian nations, which had limited class size. Since May, Israel has closed 125 schools and 258 kindergartens because of outbreaks.
Despite the Israeli numbers, there are other epidemiological case studies that indicate that spread of coronavirus can be limited in schools. In the German state of Saxony, physicians from Dresden University checked blood samples from 1,500 students and 500 teachers once schools reopened in May. Only 12 came back positive for antibodies to the coronavirus, indicating a low level of community infection. Their preliminary study, which has been posted on a preprint server and not peer-reviewed by a scientific journal, also reported that even though coronavirus cases were detected in three of the 13 schools surveyed, the infection did not spread throughout the schools or the nearby community.
Among 24 households in which at least one family member had previously tested positive for Covid-19, there was only one transmission of the virus to another family member. The study authors say that means that the schoolchildren did not get infected despite living with an infected family member, and also did not pass on the virus to other schoolchildren. “Our study finds that students play a less crucial role in transmitting the virus than initially thought,” Jakob Armann, an author of the study and a pediatric infectious disease specialist at the University Children’s Hospital in Dresden, wrote in an email.
“We could not identify any hidden clusters, even in schools that had identified cases before the March lockdown,” Arman continued. “There is a way to reopen schools safely while maintaining certain measures (e.g. universal mask wearing in public transportation, in stores, no sporting events) to keep case numbers in the general population so low that you can keep students in school at the same time.”
While the German study might be considered a bit of good news for parents who want their children to return to in-person classes, there’s a big caveat. Unlike the United States, which has been plagued by a chaotic federal response and disparate measures by individual governors, German health officials followed public health guidelines and handled the coronavirus outbreak quickly once it emerged in March. Germany instituted early and widespread testing and treatment protocols, and set up plenty of intensive care beds. German citizens also trusted their government’s instructions to take precautions and widely observed social distancing guidelines.
Since then, Germany has reopened its schools, economy and sports leagues without losing control of the virus. Germany has had 206,667 cases and 9,124 deaths as of July 26, according to the Johns Hopkins University Coronavirus Resource Center. That compares to more than 4.2 million confirmed cases and 146,831 deaths in the United States, more than any other country.
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With 2,000 participants, the German study was relatively small. In epidemiology, a larger sample size can provide the kind of statistical power to bolster a conclusion about disease spread among a population. So it's also worth looking at that study of nearly 5,700 South Korean coronavirus patients that was released this month on a preprint server by researchers at the Korean Centers for Disease Control. Through extensive contract tracing, the authors were able to track viral spread from so-called “index patients,” who are the first confirmed cases in a community cluster of infections, to the additional 59,000 people they infected. They found that children under 10 who were positive for Covid-19 had the lowest transmission rates of any age group, whereas children between 10 and 19 had transmission rates similar to adults.
The sample size of the study is impressive, but there are some issues to consider, according to William Raszka, a professor and pediatric infectious disease specialist at the University of Vermont College of Medicine. Raszka notes that the researchers did not determine whether children were asymptomatic carriers of the disease. That’s important because as many as 40 percent of those infected with Covid-19 do not show any symptoms and may be spreading it unknowingly.
He also noted that the contact tracing was done when schools were closed and children were at home. “The take-home of this study for me is that very young children are unlikely to be infected or transmit disease in households,” Raszka says. “I’ve always been concerned about older children, and concerned that the older you are, the more likely you are to transmit. A 10-year-old will act much different than a 19-year-old.” Older teens spend more time out of the house, hang out with friends, and are less likely to follow social distancing rules than younger children living at home, he added.
Raszka believes schools can reopen for younger children if officials take precautions and testing is available once students or teachers become ill. “I don’t think you can make schools zero risk,” Raszka says. “But with the right mitigation strategies and the right policies at the district or state level you can make it low risk. Schools will look different.”
In the coming weeks, school board members and superintendents around the US will (hopefully) be relying on expert advice and scientific studies to determine whether to open their schools to in-person learning, and if so, how to manage the risk. Others might bend to political pressure from governors or the president, who has threatened to withhold federal education money if schools don’t reopen their classrooms. (It’s not clear if the administration can legally do this, and whether state or local school authorities would be affected.)
In places where the virus continues to rage, like Florida, Texas, and California, it may seem clear that online learning would be the safer bet for now. “When you have such surges of disease in the community, you are basically asking for trouble if you open schools,” says Tina Q. Tan, professor of pediatrics, Northwestern University and board member of the Infectious Diseases Society of America.
However, many school districts are somewhere in the middle: infections aren’t out of control, but the virus is still persistent. School officials there have to weigh the risks to teachers and students of opening classrooms against the psychological isolation and emotional harm of keeping kids at home all day for another six months. Experts say time is running short. Even if local authorities shut down public spaces and require masks and social distancing for everyone immediately, it would take several weeks to slow the spread of Covid-19, says Leana Wen, professor of public health at George Washington University and former Baltimore health commissioner.
“We saw what happens when we try to take shortcuts,” Wen said about the recurrence of Covid-19 cases after some states opened too fast in May and June. Opening schools without precautions, protocols and adequate testing, Wen says, “is not going to be effective and it’s going to cost lives.”