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As schools reopen amid COVID-19 pandemic, how long do asymptomatic children remain contagious?

By Quentin Fottrell

New insights into coronavirus transmission among children shed light on the pandemic at an important time for families, communities and public-health officials

Should families double down on social distancing now that their kids are going back to school?

A new study published in JAMA Pediatrics suggests that children can shed SARS-CoV-2, the virus that causes COVID-19, even if they never develop symptoms or even for long after symptoms have cleared. It found a significant variation in how long children continued to shed virus through their respiratory tract and, therefore, could potentially remain infectious.

While the virus was detectable for an average of about 2.5 weeks in the entire group, a significant portion of the children --about a fifth of the asymptomatic patients and about half of the symptomatic ones -- were still shedding virus at the three week mark. The latest study in the peer-reviewed JAMA Pediatrics said the duration of symptoms also varied widely, from three days to nearly three weeks.

A recent systematic review estimated that 16% of children with SARS-CoV-2 infection are asymptomatic, but evidence suggests that as many as 45% of pediatric infections are asymptomatic, according to the Centers for Disease Control and Prevention. The signs and symptoms of COVID-19 in children are similar to other infections and noninfectious processes, including influenza.

While children infected with SARS-CoV-2 are less likely than adults to develop severe illness or complications, they are still at risk of becoming ill. "Recent COVID-19 hospitalization surveillance data shows that the rate of hospitalization among children is low (8 per 100,000 population) compared with that in adults (164.5 per 100,000 population)," the CDC said.

Such research comes at an important time for families and communities. Amid pressure from the teachers union to delay the start of the school year, New York City Mayor Bill de Blasio announced Tuesday (link) that in-person classes will be pushed back until Sept. 21, 11 days later than planned. Remote learning, also originally slated to start on Sept. 10, will now commence on Sept. 16.

Other countries have not fared so well with school reopenings. Israel, which also reopened schools this week, had less success when it reopened schools on May 17 (link) amid high temperatures that made it difficult for students to wear masks, full classrooms that made social distancing near-impossible and, perhaps, the illusion that the virus had been vanquished, creating a false sense of security.

The risk, as Israel discovered, is providing an environment where children unwittingly spread the virus to each other, which can lead to community transmission. That's particularly worrying for those who have underlying conditions and the elderly who are more vulnerable to the most severe effects of the virus. Community transmission also makes contact tracing more difficult.

A school outbreak can lead to community, hence staggered school reopenings, social distancing and reduced class sizes. "If we find a certain number of symptomatic people testing positive, we expect the same number of asymptomatic carriers that are much more difficult to identify and isolate," said Enrico Lavezzo, a professor in the University of Padua's department of molecular medicine.

The latest study in JAMA Pediatrics focused on 91 pediatric patients followed at 22 hospitals throughout South Korea. "Unlike in the American health system, those who test positive for COVID-19 in South Korea stay at the hospital until they clear their infections even if they aren't symptomatic," said Roberta DeBiasi, chief of the Division of Infectious Disease at the Children's Hospital in Washington, D.C.

The patients here were identified for testing through contact tracing or developing symptoms. About 22% never developed symptoms, 20% were initially asymptomatic but developed symptoms later, and 58% were symptomatic at their initial test. The hospital staff tested them every three days on average, providing a picture of how long viral shedding continues over many weeks.

Among the important findings from the study: Children, a group widely thought to develop mostly mild disease that quickly passes, can shed virus for weeks, DeBiasi and Meghan Delaney, chief of the Division of Pathology and Lab Medicine at the Children's National Hospital in Washington, D.C., wrote in a commentary piece to accompany the study in JAMA Pediatrics.

Other key points: Even asymptomatic children continued to shed coronavirus after testing positive, making them potential key vectors. In this study at least, there were a large number of asymptomatic patients: About one-fifth of the group in South Korean hospitals. They said the study provides important insight on the role children might play in the spread of COVID-19.

But the study also has obvious limitations. One of these relates the link between testing and transmission. A "positive" or "negative" result may not necessarily mean that a child is infectious, "with some positives reflecting bits of genetic material that may not be able to make someone sick," or, on the other hand, "negatives reflecting low levels of virus that may still be infectious."

They may have tested different parts of the respiratory tract and different testers may yield different results. It's unclear whether symptomatic children shed different quantities of virus than symptomatic patients. They tested for the active virus -- not antibodies -- excluding those who may have had and cleared an asymptomatic or mild infection, an important factor for understanding herd immunity.

However, DeBiasi said studies such as these can add to the knowledge of public-health efforts being developed and refined to bring COVID-19 under control. "Each of these pieces of information that we, our collaborators and other scientists around the world are working to gather is critical for developing policies that will slow the rate of viral transmission in our community," she said.

As of late Wednesday, COVID-19 has infected 25,773,958 people worldwide, which mostly does not account for asymptomatic cases, and killed 857,552. The U.S. still has the world's highest number of COVID-19 cases (6,075,652), followed by Brazil (950,931), India (3,769,523) and Russia (1,001,965), according to data aggregated by Johns Hopkins University (link).

In the meantime, cases keep rising in the U.S. with California becoming the first state in the country to surpass 700,000 confirmed cases; infections there hit 715,617 as of Tuesday with 13,150 COVID-related deaths. New York has recorded 435,510 infections and the highest number of deaths in the U.S. (32,966). COVID has killed 184,689 people in the U.S.

AstraZeneca AZN, -1.10% (link) , in combination with Oxford University; BioNTech SE BNTX, -5.61% (link) and partner Pfizer PFE, -2.40% (link) ; GlaxoSmithKline GSK, -1.61% (link) ; Johnson & Johnson JNJ, -1.23% (link) ; Merck & Co. MERK, -0.31% (link) ; Moderna MRNA, -2.41% (link) ; and Sanofi SAN, -1.34% (link) are among those currently working toward COVID-19 vaccines.

The Dow Jones Industrial Index DJIA, +0.75% (link), the S&P 500 SPX, +0.75% (link) and the Nasdaq Composite COMP, +1.39% (link) all ended higher Tuesday. Over the past five months, the Dow's advanced 30%, its biggest 5-month percent gain since July 2009, while the S&P 500 added over 35%, its best 5-month run since October 1938.

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09-02-20 0640ET

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