Infectivity of SARS-CoV-2 in children compared with adults

1. Children are most likely not the dominant drivers of COVID-19 transmissions, as their COVID test specimens were not as likely to grow in culture, had higher cycle thresholds in RT-PCR, and had lower viral concentrations, compared to adult specimens.

Evidence Rating Level: 2 (Good)

Although the pediatric population is a substantial driver of common viral transmissions, such as the flu, there is conflicting evidence surrounding the extent of their role in COVID-19 transmissions. For instance, some studies have shown higher viral loads in children, whereas others have shown similar levels in children and adults. However, no known studies have compared children and adults using other measures of transmissibility, such as a positive viral culture, cycle threshold from PCR, and the 50% tissue culture infective dose (TCID₅₀/mL) which is the amount of virus required to kill half of the culture cells. The current study based in Manitoba, Canada collected nasopharyngeal swab tests from COVID-19 patients and their contacts, to compare these metrics between children and adults. In total, 305 specimens were cultured: 130 adult specimens, 78 from children aged 11-17, and 97 from children aged 10 and under. A positive viral culture was produced in 44% of adult samples (95% CI 35-53%), 19% of 10 and younger samples (95% CI 11-28%), and 23% of 11-17 year old samples (95% CI 14-34%). Compared to the adult samples, the p-values were 0.003 and < 0.001 respectively for the 11-17 and under 10 age groups, and no significant difference was found between the pediatric age groups (p = 0.5). 48% of children under 10 had asymptomatic infections, compared to 24% of the 11-17 group and 7% of adults. Additionally, the cycle threshold for RT-PCR was lowest in adults (18.7, IQR 17.9-30.4) compared to 22.2 in the 11-17 age group (IQR 18.3-29.0, p = 0.02) and 25.1 in the under 10 age group (IQR 17.7-31.3, p < 0.001). Lower cycle thresholds indicate higher quantities of viral genetic material in the samples. As well, the median TCID₅₀/mL was lower in the 11-17 group (316, IQR 178-2125) compared to adults (5620, IQR 1171-17800, p < 0.001), but the results for the under 10 group and adults were not significantly different. Overall, the study demonstrated that the pediatric population is less likely to drive COVID-19 transmissions, which has implications for public health measures concerning this population, such as re-opening schools and daycares.

Click to read the study in CMAJ

Image: PD

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