Association of SARS-CoV-2 viral load distributions with individual demographics and suspected variant type: results from the Liverpool community testing pilot, England, 6 November 2020 to 8 September 2021

Background: The PCR quantification cycle (C-q) is a proxy measure of the viral load of a SARS-CoV-2-infected individual. Aim: To investigate if C-q values vary according to different population characteristics, in particular demographic ones, and within the COVID19 pandemic context, notably the SARS-CoV-2 type/variant individuals get infected with. Methods: We considered all positive PCR results from Cheshire and Merseyside, England, between 6 November 2020 and 8 September 2021. C-q distributions were inspected with Kernel density estimates. Multivariable quantile regression models assessed associations between people's features and C-q. Results: We report C-q values for 188,821 SARS-CoV-2 positive individuals. Median C(q)s increased with decreasing age for suspected wildt-ype virus and Alpha variant infections, but less so, if not, for Delta. For example, compared to 30-39-yearolds (median age group), 5-11-year-olds exhibited 1.8 (95% CI: 1.5 to 2.1), 2.2 (95% CI: 1.8 to 2.6) and 0.8 (95% CI: 0.6 to 0.9) higher median C(q)s for suspected wild-type, Alpha and Delta positives, respectively, in multivariable analysis. 12-18-year-olds also had higher C(q)s for wild-type and Alpha positives, however, not for Delta. Overall, in univariable analysis, suspected Delta positives reported 2.8 lower median C-q s than wild-type positives (95% CI: 2.7 to 2.8; p < 0.001). Suspected Alpha positives had 1.5 (95% CI: 1.4 to 1.5; p < 0.001) lower median C(q)s than wild type. Conclusions: Wild-type-or Alpha-infected school-aged children (5-11-year-olds) might transmit less than adults (> 18 years old), but have greater mixing exposures. Smaller differences in viral loads with age occurred in suspected Delta infections. Suspected-Alpha- or Delta-infections involved higher viral loads than wild type, suggesting increased transmission risk. COVID019 control strategies should consider age and dominant variant.

Automated summary

This study investigated whether the PCR quantification cycle (C-q) values of SARS-CoV-2-infected individuals vary according to different population characteristics, particularly demographic ones, and within the context of the COVID-19 pandemic, notably the SARS-CoV-2 type/variant individuals get infected with. The study found that younger age was associated with higher C-q values for suspected wild-type and Alpha variant infections, but less so for Delta variant. The study suggests that age and dominant variant should be considered in COVID-19 control strategies.