Nature: How children spread coronaviruses? Scientists still don't know!

June 1, 2020 /
BiovalleyBIOON/ -- The role of children in the transmission of coronaviruses has been a key issue since the beginning of the pandemicNow, scientists are trying to solve the problem as some countries allow schools to reopen after weeks of closurechildren make up only a small proportion of confirmed COVID-19 cases -- less than 2 percent of reported infections in China, Italy and the United States are under the age of 18but researchers are divided on whether children are less susceptible to infection and transmission of the virus than adultsSome say there is growing evidence that children are at lower risk of diseaseAlasdair Munro, a paediatric infectious disease researcher at the University Hospital of Southampton in the UK, said they did not lead to most of the spread, so the data supported the opening of schoolschildren from Germany and Denmark have returned to school, and students from some parts of Australia and France will be returning in the coming weeksother scientists objected to rushing back to the classroomThey say children have lower infection rates than adults, in part because they are less exposed to the virus, especially if many schools are closedChildren are not checked as often as adults because they tend to have mild or no symptoms, the researchers saidGary Wong, a researcher in paediatric respiratory medicine at the Chinese University of Hong Kong,, said: "I don't think there is any strong biological or epidemiological reason to believe that children will not be infected in this critical wayAs long as there is community transmission in the adult population, the reopening of schools may facilitate transmission, as respiratory viruses are known to spread in schools and day careHe said a good monitoring and testing system should be in place before school starts scientists say the number of infections could soar in the coming weeks in countries where children have returned to school if the virus is transmitted but to address this debate, large-scale, high-quality population studies -- some of which are already under way -- include testing for the presence of antibodies in the blood as a sign of previous infections other scientists are studying the child's immune response to find out why children have milder symptoms than adults after contracting the virus, and whether this provides clues to potential treatments susceptible controversy
a study published April 27 in The Lancet Infectious Diseases analyzed families in Shenzhen, China, that had confirmed COVID-19 cases The study found that children under the age of 10 are just as susceptible to infection as adults, but are less likely to develop severe symptoms "This preprint really scares everyone," Munro said, because it suggests that children may be spreading the infection in silence image source: https://cn.bing.com
but other studies, including from South Korea, Italy and Iceland, have found that children have lower infection rates in countries where tests are more common Some studies from China also support the idea that children are less susceptible to infection One of them, published April 29 in the journal Science, analyzed data from Hunan, where contacts with known infected people have been tracked and tested The authors found that for every child under the age of 15 who was infected, nearly three people between the ages of 20 and 64 were infected However, Munro said the data were not conclusive for teens 15 years of age or older and showed that their risk of infection was similar to that of adults the risk of transmission
more puzzling is whether infected children transmit the virus in a similar way to adults A study of a group of cases in the French Alps described the condition of a 9-year-old child who showed symptoms of COVID-19 while attending three schools and a ski class, but did not infect anyone "It's almost unheard of for an adult to be exposed to so many people without infecting anyone else Munro said Kirsty Short, a virologist at the University of Queensland in Brisbane, Australia, led an unpublished meta-analysis study involving several family studies, including from countries such as Singapore that had not closed schools at the time She found that children were rarely the first to bring the virus home: they found the first case in about 8 percent of households By contrast, about 50 percent of households have seen children's cases during the h5N1 outbreak of avian influenza , the study said "Family research is reassuring because even if there are a lot of infected children, they don't go home and infect others," said Munro, "
but Wong thinks such studies are biased because these families are not randomly selected, but because there is already a known infected adult So it's also hard to determine who introduced the virus, he said Closing schools and day care may also explain why children are not usually the main source of SARS-CoV-2 infection Other respiratory viruses can spread from adults to children and then back, he said, so "I don't think the virus is an exception." in fact, two preprinted reports say that viral RNA levels in children with COVID-19 symptoms may be similar to those in adults "Based on these results, we must warn that schools and kindergartens are not being reopened without restriction in the current circumstances "One of the studies was led by Christian Drosten, a virologist at Berlin's Charlett Hospital However, Harish Nair, an epidemiologist at the University of Edinburgh in the UK, said it was unclear whether high levels of viral RNA could be used as an indicator of a person's infectiousness there is very little research on the spread from schools to the wider community, but an ongoing Australian study shows that this spread is limited and much lower than that of other respiratory viruses such as influenza Of the more than 850 people who had contact with nine students and nine staff in NSW, only two children had recorded COVID-19 cases with these contacts Munro said that based on the evidence, children should be allowed to return to school "Children get the least benefit from the blockade, and they lose a lot," he said, "for example, missing out on education and not getting extra social support, such as free school meals." Short said the reopening of schools does not mean that everything is back to normal She says there will be a lot of restrictions and changes, such as separating desks in classrooms and closing playgrounds to reduce the risk of transmission As schools reopen, it's also important to study the spread of schools, Wong said Researchers in the Netherlands plan to monitor the situation closely in the coming weeks as schools become open image source: https://cn.bing.com
immune response
However, the researchers do agree that children tend to respond better to COVID-19 than adults Most infected children have mild or asymptomatic symptoms, but some are indeed seriously ill or even dead There have been reports of a small number of children in London and New York experiencing inflammatory reactions similar to those of the rare kawashei disease in children "I wouldn't be surprised if COVID-19 is related to Kawasaki disease, because many other viral infections are also associated with Kawasaki disease," Wong said If the link turns out to be true, he says, it could be ignored in China, Japan and South Korea, where Kawasaki is much more common Wong says one theory could explain why most children have milder symptoms: children's lungs may contain fewer or less mature ACE2 receptors, the proteins used by SARS-CoV-2 virus into cells But to prove it, researchers needed to study tissue samples from children, which Wong said were difficult to obtain also believe that children are more often exposed to other coronaviruses, such as the coronavirus that causes the common cold, which protects them from serious diseases "But it doesn't seem to work much, because even newborn babies don't seem to get very serious illnesses from coronary virus infection," Munro said "
Wong believes that children may have a more appropriate immune response to infection -- enough to fight the virus, but not strong enough to cause significant damage to their organs His preliminary analysis of 300 patients infected with COVID-19 found that children produced much lower levels of cytokines (proteins released by the immune system) Patients of all ages with serious illnesses tend to have higher levels of cytokine, he said But he still needs to sort out the cause and effect "Do they get sick because they have higher cytokine levels, or do they get sicker and cause higher cytokine levels?" (biovalleybioon.com) References: 1
How do children spread the coronavirus? The science still still isn't clear
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Changes in contact patterns shape the dynamics of the COVID-19 outbreak in Chin
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