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One of the most important unanswered questions about Covid-19 is this: What role do children play in maintaining the pandemic?
There appear to be fewer children infected with the coronavirus than adults, and most children with mild symptoms, if any. But do they transmit the virus to adults and continue the chain of transmission?
The answer is key to deciding whether and when to reopen schools, a step that President Trump urged states to consider before summer.
Two new studies offer compelling evidence that children can transmit the virus. Neither showed it, but the evidence was strong enough to suggest that schools should be kept closed for now, many epidemiologists who were not involved in the research said.
In some of these countries, the community transmission rate is low enough to take the risk. But in others, including the United States, the reopening of schools may push the epidemic. Reproduction number: The number of new infections estimated to come from a single case, commonly known as R0, at dangerous levels, epidemiologists warned after reviewing the results of the new studies.
Based on their data, the researchers estimated that closing schools alone is not enough to stop an outbreak, but it can reduce the increase by 40 to 60 percent and delay the course of the epidemic.
“My simulation shows that yes, if you reopen the schools, you will see a huge increase in the number of reproduction, which is exactly what you don’t want,” said Marco Ajelli, a mathematical epidemiologist who did the work while at the Bruno Foundation. Kessler in Trento, Italy.
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The second study, carried out by a group of German researchers, was more direct. The team evaluated children and adults and found that children who test positive have the same amount of virus as adults, sometimes more, so they are presumably just as infectious.
Are any of these studies definitive? The answer is “No, of course not,” said Jeffrey Shaman, an epidemiologist at Columbia University who was not involved in any of the studies. But, he said, “opening schools because of some unresolved notion that children aren’t really involved in this, that would be silly.”
The German study was led by Christian Drosten, a virologist who has It amounted to something like celebrity status in recent months for his candid and straightforward comment on the pandemic. Dr. Drosten runs a large virology laboratory in Berlin that has tested over 60,000 people for the coronavirus. According to other studies, he and his colleagues found many more infected adults than children.
The team also analyzed a group of 47 infected children between the ages of 1 and 11. Fifteen of them had an underlying condition or were hospitalized, but the rest were largely symptom-free. Asymptomatic children had viral loads that were as high or higher than symptomatic children or adults.
“In this cloud of children, there are these few children who have a very high virus concentration,” said Dr. Drosten.
He noted that there is a great deal of work to suggest that a person’s viral load closely tracks their infectivity. “So I am a little reluctant to happily recommend to politicians that we can now reopen nurseries and schools.”
Many statisticians contacted him via Twitter suggesting one or the other more sophisticated analysis. His team implemented the suggestions, Dr. Drosten said, and even invited one of the statisticians to collaborate.
“But the message of the document has not really been changed by any more sophisticated statistical analysis,” he said. For the United States to even consider reopening schools, he said, “I think it’s too soon.”
In the China study, the researchers created a matrix of contacts of 636 people in Wuhan and 557 people in Shanghai. They called each of these people and asked them to remember all the people they had contact with the day before the call.
They defined a contact as a face-to-face conversation involving three or more words or physical contact, such as a handshake, and asked for the age of each contact, as well as the relationship with the survey participant.
Comparing the blockade to a 2018 Shanghai benchmark survey, they found that the number of contacts during the blockade decreased by a factor of about seven in Wuhan and eight in Shanghai.
“There was a big decrease in the number of contacts,” said Dr. Ajelli. “In both places, that explains why the epidemic was brought under control.”
The researchers also had access to a rich dataset from the Hunan Province Center for Disease Control and Prevention. Province officials tracked 7,000 contacts from 137 confirmed cases, observed them for 14 days, and analyzed them for coronavirus infection. They had information not only for people who got sick, but also for those who became infected and remained asymptomatic, and for anyone who remained virus-free.
Hospital or household data tends to focus only on symptomatic or seriously ill people, Dr. Ajelli noted. “This type of data is better.”
The researchers stratified the data from these contacts by age, and found that children between the ages of 0 and 14 are approximately one-third less susceptible to coronavirus infection than those aged 15 to 64, and adults 65 and older. they are more susceptible in approximately 50 percent.
They also estimated that closing schools can reduce the number of reproductions, again, the estimate of the number of infections linked to a single case, by approximately 0.3; an epidemic begins to grow exponentially once this metric exceeds 1.
In many parts of the United States, the number is already around 0.8, Dr. Ajelli said. “If it’s that close to the threshold, an addition of 0.3 can be devastating.”
However, some other experts pointed out that keeping schools closed indefinitely is not only impractical, but can cause lasting harm to children.
Jennifer Nuzzo, an epidemiologist at the Johns Hopkins University Bloomberg School of Public Health, said the decision to reopen schools cannot be made solely to try to prevent transmission.
“I think we need to have a holistic view of the impact of school closings on children and our families,” said Dr. Nuzzo. “I am concerned at some point, the cumulative damage from the measures may exceed the harm to children from the virus.”
E-learning approaches can temporarily provide children with a routine, “but any parent will tell them that they are not really learning,” he said. Children have been known to fall back during the summer months, and adding several more months to that could permanently hurt them, and particularly those already struggling.
“I’m not saying we absolutely need to rip off the band-aid and reopen schools tomorrow,” he said, “but we have to consider these other endpoints.”
But other experts said the study was not well designed because it looked at home transmission. Unless scientists have deliberately evaluated everyone, they would have noticed and tested only more serious infections, which tend to occur among adults, said Bill Hanage, an epidemiologist at Harvard T.H. Chan School of Public Health.
“The assumptions that children are not involved in epidemiology, because they don’t have a serious illness, are exactly the kind of assumption that really needs to be questioned in a pandemic,” said Dr. Hanage. “Because if it’s wrong, it has really disastrous consequences.”
All the experts agreed on one thing: that governments should have active debates about what the reopening of schools is like. Students could be scheduled to come to school on different days to reduce the number of people in the building at one time, for example; desks can be placed six feet away; and schools could prevent students from meeting in large groups.
Teachers with older or underlying health conditions should be able to opt out and receive alternative jobs outside of the classroom, if possible, Dr. Nuzzo said, and children with underlying conditions should continue to learn from home.
The leaders of the two new studies, Dr. Drosten and Dr. Ajelli, were more circumspect, saying their role is simply to provide data that governments can use to make policy.
“In some ways I am the bearer of bad news, but I cannot change the news,” said Dr. Drosten. “It’s in the data.”
