Virologic features of SARS-CoV-2 infection in children

Abstract

Background: Data on pediatric COVID-19 has lagged behind adults throughout the pandemic. An understanding of SARS-CoV-2 viral dynamics in children would enable data-driven public health guidance.

Methods: Respiratory swabs were collected from children with COVID-19. Viral load was quantified by RT-PCR; viral culture was assessed by direct observation of cytopathic effects and semiquantitative viral titers. Correlations with age, symptom duration, and disease severity were analyzed. SARS-CoV-2 whole genome sequences were compared with contemporaneous sequences.

Results: 110 children with COVID-19 (median age 10 years, range 2 weeks-21 years) were included in this study. Age did not impact SARS-CoV-2 viral load. Children were most infectious within the first five days of illness, and severe disease did not correlate with increased viral loads. Pediatric SARS-CoV-2 sequences were representative of those in the community and novel variants were identified.

Conclusions: Symptomatic and asymptomatic children can carry high quantities of live, replicating SARS-CoV-2, creating a potential reservoir for transmission and evolution of genetic variants. As guidance around social distancing and masking evolves following vaccine uptake in older populations, a clear understanding of SARS-CoV-2 infection dynamics in children is critical for rational development of public health policies and vaccination strategies to mitigate the impact of COVID-19.

Keywords: Pediatric COVID-19; SARS-CoV-2; Viral dynamics.

Figure 1:

COVID-19 disease severity and SARS-CoV-2 viral load across age groups. A. Age of pediatric patients with SARS-CoV-2 infection, stratified by disease severity: asymptomatic (n=27), mild disease, outpatient (n=48), moderate/severe COVID-19, hospitalized (n=18). Analyzed by ordinary one-way ANOVA. B. SARS-CoV-2 viral load was quantified across a range of disease severities. Patients presenting with ≤10 days of symptoms were compared, including asymptomatic pediatric outpatients (n=27), mildly symptomatic pediatric outpatients (n=44), moderate/severe pediatric hospitalized patients with oxygen requirement (n=18), and moderate/severe adult hospitalized patients (n=29). Analyzed by ordinary one-way ANOVA. C. Viral load for each specimen (n=110) was determined by qPCR, plotted against participant age and analyzed by Pearson correlation. D. Viral load levels reported by school age group: 0–4 years old (yo)– infant through pre-school (n=32), 5–10yo – elementary school (n=23), 11–16yo – middle school (n=33), 17yo and over – high school and higher education (n=22). Analyzed by ordinary one-way ANOVA. Dotted lines depict limit of detection. * P<0.05, *** P<0.001, **** P< 0.0001, ns = not significant

Figure 2:

SARS-CoV-2 culture results across age groups and viral load. A–B. Samples with observable CPE (culture +) (n=31) or without observable CPE (culture −) (n=95) plotted against viral load (A) and participant age (B) and compared using t test. C–D. Semiquantitative viral titer expressed as TCID50/mL for culture positive samples plotted against corresponding viral load (C) or participant age (D), Analyzed using Pearson correlation. Dotted line depicts limit of detection. **** P < 0.0001

Figure 3:

Culture positivity and duration of symptoms. A. Viral load for each specimen was determined by qPCR and plotted against the duration of symptoms (in days). Analysis by Pearson correlation. B. Viral load reported by binned duration of symptoms. Ordinary one-way ANOVA used for analysis. C. Duration of symptoms for samples with observable CPE (culture +, n=29) and without observable CPE (culture −, n=85). Analysis by t test. D. Semiquantitative viral titer reported by binned duration of symptoms, analyzed by ordinary one-way ANOVA. Dotted lines depict limit of detection. ** P < 0.01, **** P < 0.0001

Figure 4:

Correlation of viral load with age and duration of illness based on disease severity. A. Correlation of viral load and age, stratified by asymptomatic (n=30), mild outpatient (n=48) and moderate/severe hospitalized (n=18) cohorts. B. Viral load of hospitalized adult (n=29), hospitalized pediatric participants requiring respiratory support (n=18) and pediatric outpatients with mild disease (n=48), plotted against duration of symptoms. Dotted lines depict limit of detection.

Figure 5.

Phylogenetic analysis of pediatric and community SARS-CoV-2 sequences. Maximum likelihood tree generated from pediatric sequences (red) and 183 contemporaneous Massachusetts sequences from GISAID.