Age and Sex Modulate SARS-CoV-2 Viral Load Kinetics: A Longitudinal Analysis of 1735 Subjects

Abstract

The COVID-19 pandemic caused by SARS-CoV-2 represents a public health emergency, which became even more challenging since the detection of highly transmissible variants and strategies against COVID-19 were indistinctly established. We characterized the temporal viral load kinetics in individuals infected by original and variant strains. Naso-oropharyngeal swabs from 33,000 individuals (admitted to the IRCCS Santa Lucia Foundation Drive-in, healthcare professionals and hospitalized patients who underwent routinary screening) from November 2020 to June 2021 were analyzed. Of them, 1735 subjects were selected and grouped according to the viral strain. Diagnostic analyses were performed by CE-IVD RT-PCR-based kits. The subgenomic-RNA component was assessed in 36 subjects using digital PCR. Infection duration, viral load decay speed, effects of age and sex were assessed and compared by extensive statistical analyses. Overall, infection duration and viral load differed between the groups (p < 0.05). Male sex was more present among both original and variant carriers affected with high viral load and showing fast decay speed, whereas original strain carriers with slow decay speed resulted in older (p < 0.05). Subgenomic-RNA was detected in the positive samples, including those with low viral load. This study provides a picture of the viral load kinetics, identifying individuals with similar patterns and showing differential effects of age and sex, thus providing potentially useful information for personalized management of infected subjects.

Keywords: COVID-19; SARS-CoV-2; age; duration of infection; precision medicine; sex; subgenomic-RNA; viral load.

Figure 1

Comparison of OSs and αV carrier individuals. (A) The duration of infection significantly differed between OSs and αV carriers. The average day of resolution of infection is reported for each group. (B) Viral load and VLDS are shown between groups. Carriers of αV were found with a higher viral load (p < 0.03); *** p < 0.001.

Figure 2

Analysis of the OSs carriers group. (A) VLDS showed to be dependent on the basal viral load, proving the need of stratifying according to viral load inside the group. (B) The duration of infection significantly differs among individuals with different VLDS. (C) Age was found to be significantly different between individuals with low and high viral loads. (D) Sex distribution was different among individuals with different ranges of viral load. Male sex was found to be significantly present in the group of individuals with high and medium viral loads characterized by fast VLDS. n= number of subjects; * p < 0.05; *** p < 0.001.

Figure 3

Analysis of the αV carriers group. (A) VLDS showed to be dependent on the basal viral load, proving the need of stratifying according to viral load inside the group. (B) The duration of infection significantly differs between individuals with slow and fast VLDS. (C) Age did not show a significant difference with respect to individuals with different VLDS. (D) Sex distribution was different among individuals with a high viral load. Male sex was found to be significantly different between the individuals characterized by fast and medium as well as slow and medium VLDS. n= number of subjects; *** p < 0.001; ns: not significant.

Figure 4

Assessment of sg-RNA component. (A) Representation of the sg-RNA concentration and corresponding viral load decay over time. (B) sg-RNA concentration and corresponding viral load reported for the deemed timepoints. Both sg-RNA concentration and viral load are reported in log₁₀ copies/mL.