Viral infectivity in paediatric SARS-CoV-2 clinical samples does not vary by age

Abstract

At the start of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, there was much uncertainty about the role of children in infection and transmission dynamics. Through the course of the pandemic, it became clear that children were susceptible to SARS-CoV-2 infection, although they were experiencing a notable lack of severe disease outcomes as compared to the adult population. This trend held true with the emergence of new SARS-CoV-2 variants, even in paediatric populations that were ineligible to be vaccinated. The difference in disease outcomes has prompted questions about the virological features of SARS-CoV-2 infection in this population. In order to determine if there was any difference in the infectivity of the virus produced by children with coronavirus disease 2019 (COVID-19), we compared viral RNA levels (clinical RT-qPCR C _T) and infectious virus titres from 144 SARS-CoV-2-positive clinical samples collected from children aged 0 to 18 years old. We found that age had no impact on the infectiousness of SARS-CoV-2 within our cohort, with children of all ages able to produce high levels of infectious virus.

Keywords: SARS-CoV-2; clinical isolates; paediatric; viral infectivity.

Fig. 1.

SARS-CoV-2 viral infectivity does not vary by age in a paediatric population. (a) A set of 144 clinical samples from children infected with SARS-CoV-2 was used to examine the relationship between infectious virus titre and RNA viral load as a function of patient age. Individual specimen measurements of E gene RNA levels (C _T) on the x-axis are plotted against viral titre, as measured in focus forming units (f.f.u. ml⁻¹) on the y-axis. Dashed line indicates the limit of detection for infectious titre (20 f.f.u. ml⁻¹). Samples for which we could not measure a viral titre were assigned fixed values of one-tenth the limit of detection (2 f.f.u. ml⁻¹). Lines of best fit were generated by linear regression on log-transformed titre data as a function of C _T and age group. Symbol and colour indicate age group (<1, purple circle; 1–5, blue square; 6–11, turquoise diamond; 12–17, green triangle). (b) During the time of sample acquisition, epidemiological data about SARS-CoV-2 variants were obtained in Milwaukee, Wisconsin, USA. Sequencing prior to January 2021 indicates the presence of ancestral (pre-VOC) SARS-CoV-2, and post January 2021 through June 2021 sequencing primarily detects the alpha variant. The epidemiological data collected include both adult and paediatric samples and are subject to sampling bias. The number of samples sequenced per day varied from 0 to 83. The solid line indicates the 7 day rolling average of the percentage of sequences with mutations, and the shaded area represents the 95 % confidence interval. Sequencing data adapted from outbreak.info, April 2021 [14].