Total and subgenomic RNA viral load in patients infected with SARS-CoV-2 Alpha, Delta, and Omicron variants.

BACKGROUND: SARS-CoV-2 genomic and subgenomic RNA levels are frequently used as a correlate of infectiousness. The impact of host factors and SARS-CoV-2 lineage on RNA viral load is unclear.

METHODS: Total nucleocapsid (N) and subgenomic N (sgN) RNA levels were measured by RT-qPCR in specimens from 3,204 individuals hospitalized with COVID-19 at 21 hospitals. RT-qPCR cycle threshold (Ct) values were used to estimate RNA viral load. The impact of time of sampling, SARS-CoV-2 variant, age, comorbidities, vaccination, and immune status on N and sgN Ct values were evaluated using multiple linear regression.

RESULTS: Ct values at presentation for N (mean ±standard deviation) were 24.14±4.53 for non-variants of concern, 25.15±4.33 for Alpha, 25.31±4.50 for Delta, and 26.26±4.42 for Omicron. N and sgN RNA levels varied with time since symptom onset and infecting variant but not with age, comorbidity, immune status, or vaccination. When normalized to total N RNA, sgN levels were similar across all variants.

CONCLUSIONS: RNA viral loads were similar among hospitalized adults, irrespective of infecting variant and known risk factors for severe COVID-19. Total N and subgenomic RNA N viral loads were highly correlated, suggesting that subgenomic RNA measurements adds little information for the purposes of estimating infectivity.