An analysis of over 800 pediatric cases of the novel coronavirus infection has revealed that most asymptomatic children have significantly low levels of the virus compared to those who experience symptoms, findings which raise concern about the use of low sensitivity diagnostic tests for screening the pediatric population.
However, the study, published in the Journal of Clinical Microbiology, cautioned that the reason for this finding is unclear, while it also remains to be explained how lower viral loads impact the risk of COVID-19 transmission.
"While these findings provide some reassurance about the safety of asymptomatically infected children attending school, these unanswered questions suggest that risk mitigation measures in daycares, schools and the community remain critical to reduce the spread of COVID-19," said study first author Larry Kociolek, a pediatric infectious diseases expert at Ann & Robert H. Lurie Children''s Hospital in the US.
"Children must continue to wear masks, maintain social distance and wash their hands frequently," Kociolek said.
According to the scientists, it is still difficult to predict which children are likely to carry more or less virus.
"Because in every age group we tested, there were some asymptomatic kids with a higher viral load. However, even the groups of asymptomatic kids with highest viral load in our study still had lower viral loads than the children with symptoms," Kociolek said.
In the study, the scientists assessed 339 asymptomatic and 478 symptomatic children (ages 0-17 years), who were screened positive for COVID-19 using PCR tests at nine children''s hospitals across the US and Canada.
The analysis showed that asymptomatic children with diabetes and/or recent contact with a COVID-19 case, as well as those tested for surveillance purposes had significantly higher estimated risk of the highest viral burden.
According to the scientists, the finding suggests that the timing of infection relative to diagnostic testing impacted the viral loads in the asymptomatic kids in the study.
However, they also noted that even in the asymptomatic surveillance sub-cohort with highest viral loads, average levels of the virus were still significantly lower than in the symptomatic cohort.
"We now need to know what the peak viral loads are in asymptomatic kids with COVID-19 -- did the timing of testing just miss the peak in many of the asymptomatic kids in this study, or do asymptomatic kids actually have lower peak viral loads than symptomatic kids?" said study senior author Nira Pollock, Associate Medical Director of the Infectious Diseases Diagnostic Laboratory at Boston Children''s Hospital in the US.
The researchers also pointed out that the levels of the virus they found in the asymptomatic children were mostly lower than the levels that the available rapid antigen tests are able to detect.
"It is important to recognise that rapid antigen tests are less sensitive than the PCR tests used in hospitals, and that many of the asymptomatic kids in our study likely would have tested negative using the rapid tests based on our understanding of the limits of detection of those tests," Pollock said.
Based on the findings, the researchers raised caution about using low sensitivity tests for asymptomatic screening programs in pediatric populations.
"Overall, we want to encourage more studies to better understand the viral loads in asymptomatic kids -- particularly peak viral loads early in infection," Pollock added.