Illness Characteristics of COVID-19 in Children Infected with the SARS-CoV-2 Delta Variant

Abstract

Background: The Delta (B.1.617.2) SARS-CoV-2 variant was the predominant UK circulating strain between May and November 2021. We investigated whether COVID-19 from Delta infection differed from infection with previous variants in children.

Methods: Through the prospective COVID Symptom Study, 109,626 UK school-aged children were proxy-reported between 28 December 2020 and 8 July 2021. We selected all symptomatic children who tested positive for SARS-CoV-2 and were proxy-reported at least weekly, within two timeframes: 28 December 2020 to 6 May 2021 (Alpha (B.1.1.7), the main UK circulating variant) and 26 May to 8 July 2021 (Delta, the main UK circulating variant), with all children unvaccinated (as per national policy at the time). We assessed illness profiles (symptom prevalence, duration, and burden), hospital presentation, and presence of long (≥28 day) illness, and calculated odds ratios for symptoms presenting within the first 28 days of illness.

Results: 694 (276 younger (5-11 years), 418 older (12-17 years)) symptomatic children tested positive for SARS-CoV-2 with Alpha infection and 706 (227 younger and 479 older) children with Delta infection. Median illness duration was short with either variant (overall cohort: 5 days (IQR 2-9.75) with Alpha, 5 days (IQR 2-9) with Delta). The seven most prevalent symptoms were common to both variants. Symptom burden over the first 28 days was slightly greater with Delta compared with Alpha infection (in younger children, 3 (IQR 2-5) symptoms with Alpha, 4 (IQR 2-7) with Delta; in older children, 5 (IQR 3-8) symptoms with Alpha, 6 (IQR 3-9) with Delta infection ). The odds of presenting several symptoms were higher with Delta than Alpha infection, including headache and fever. Few children presented to hospital, and long illness duration was uncommon, with either variant.

Conclusions: COVID-19 in UK school-aged children due to SARS-CoV-2 Delta strain B.1.617.2 resembles illness due to the Alpha variant B.1.1.7., with short duration and similar symptom burden.

Keywords: COVID-19 symptoms; SARS-CoV-2 B.1.1.7 variant; SARS-CoV-2 B.1.617.2 variant; SARS-CoV-2 Delta strain; paediatric COVID-19.

Figure 1

Study flowchart of inclusion and exclusion criteria. Overall number for the entire cohort of children is given first. Younger children = aged 5–11 years (UK primary school-aged children). Older children = aged 12–17 years (UK secondary school-aged children). Not valid result = test result proxy-reported as “failed test” or “still waiting”. Irregular logging = proxy-reporting with intervals of more than 7 days between proxy-reports during illness.

Figure 2

Prevalence of symptoms reported over the course of illness (up to 28 days) in younger (YC, 5–11 years) and older (OC, 12–17 years) children with COVID-19 during periods of SARS-CoV-2 Alpha or Delta variant predominance.

Figure 3

Odds ratios for a symptom presenting within the first 28 days of illness in children with COVID-19 during periods of SARS-CoV-2 Delta vs. Alpha variant predominance. Results for younger (5–11 years) and older (12–17 years) children, and for the cohort overall, comparing symptom prevalence during Delta with prevalence during Alpha infection, and adjusted for age and sex. Results with statistical significance after false discovery rate test (α < 0·05) are in red.

Figure 4

Median duration and IQR of each symptom reported over the course of illness in younger (5–11 years) and older (12–17 years) children with COVID-19, whose illness lasted <28 days, during periods of SARS-CoV-2 Alpha or Delta variant predominance.