Researchers found that children infected with novel coronavirus have viral load comparable with adults admitted to ICUs. But during the early infection phase, children can have significantly higher viral load than COVID-19 adults in ICUs. Viral load decreases over time in children. Age of children did not have any impact on viral load.
Researchers Massachusetts General Hospital and Mass General Hospital for Children have found that children aged 0-22 years who have been infected with novel coronavirus (SARS-CoV-2) have viral load comparable with adults in intensive care units (ICUs) for COVID-19 treatment.
However, during their early infection phase — before symptoms develop to first two days of symptoms — children have significantly higher viral load than even the hospitalised adults with severe disease. But the viral load as measured with nasopharyngeal swab samples decreased over time in these children. Age of children did not have any impact on viral load. The study was published in The Journal of Pediatrics.
“I was surprised by the high levels of virus we found in children of all ages, especially in the first two days of infection,” Lael Yonker, director of the MGH Cystic Fibrosis Center and lead author of the study says in a release. “I was not expecting the viral load to be so high. You think of a hospital, and of all of the precautions taken to treat severely ill adults, but the viral loads of these hospitalized patients are significantly lower than a ‘healthy child’ who is walking around with a high SARS-CoV-2 viral load.”
The viral load was determined using plasma and respiratory samples (nasopharyngeal and oropharyngeal swabs) collected from children. Higher levels of viral load were detected in nasopharyngeal swabs compared with oropharyngeal swabs. No coronavirus RNA was detected in the serum samples of any children.
Children infected with coronavirus generally tend to have no or milder symptoms compared with adults and mortality too is significantly lower in children. A sub-set of children also tend to develop severe cardiac complications, including hypotension, shock, and acute heart failure.
The study involved 192 children (mean age 10.2 years), of whom 49 children tested positive for the virus while an additional 18 children had late-onset COVID-19-related illness — multisystem inflammatory syndrome. Of the 49 infected children, only 25 (51%) had symptoms including fever.
Majority of children (n=16, 34%) who tested positive for the virus were 11-16 years of age. Only two (4%) infected children were less than one year of age. Children aged one-four years were most likely to have severe complications.
Of the 49 infected children, nine (18%) did not have a known infected household contact, while in the case of children who developed complication, 10 (56%) did not have a known infected household contact. Schools seemed to be the place where most children were exposed to the virus as 26 of 49 (53%) infected children had attended school. None of the seven children aged less than five years tested positive for the virus or develop complications.
“The study reveals that children may be a potential source of contagion in the SARS-CoV-2 pandemic in spite of milder disease or lack of symptoms,” the authors write.
ACE2 expression in children
One of the hypotheses why children have reduced risk of infection compared with adults is due to reduced expression of ACE2 receptors where the virus binds. While ACE2 expression in the nasopharynx increases with age, no study has looked into ACE2 expression in the upper airways of children infected with coronavirus.
This study confirmed how ACE2 expression increases with age even among children. They found children younger than 10 years had lower ACE2 expression compared with older children. “Within the paediatric cohort, ACE2 expression increased with age,” they write.
The study found that ACE2 expression was “higher” in coronavirus-infected children, including those with severe complications, compared with non-infected children. However, among those infected children, ACE2 expression did not correlate with viral load. This suggests that while increased ACE2 expression increases susceptibility to coronavirus infection, once infected, children could carry “high viral loads regardless of level of ACE2 expression”.
“This suggests that regardless of disease susceptibility, children can carry high viral loads, which is a key consideration when opening up schools and day-care centres,” they mention.
Potential for virus spread in schools
Writing about controlling the spread of the virus in children once schools reopen, the authors write: “Our findings suggest that it would be ineffective to rely on symptoms or temperature monitoring to identify SARS-CoV-2 infection.” Instead, the focus should be on strategies including physical distancing, use of face masks, and/or remote learning, and screen all students for infection through routine screening.
“Without infection control measures, there is significant risk that the pandemic will persist, and children could carry the virus into the home, exposing adults who are at higher risk of developing severe disease,” they write.
The researchers did not study virus transmissibility by children. But “kids are a possible source of spreading this virus, and this should be taken into account in the planning stages for reopening schools,” Alessio Fasano, director of the Mucosal Immunology and Biology Research Center at MGH and senior author says in the release.
“During this COVID-19 pandemic, we have mainly screened symptomatic subjects, so we have reached the erroneous conclusion that the vast majority of people infected are adults. However, our results show that kids are not protected against this virus. We should not discount children as potential spreaders for this virus,” Dr Fasano says.