Influence of viral load on severity and mortality in COVID-19.

Background: The relationship between the initial viral load in respiratory specimens and the severity of COVID-19 is not fully elucidated. Studies on the impact of patient age on the SARS-CoV-2 load have yielded divergent results.

Objective: We aimed to investigate the impact of viral load in COVID-19.

Methods: We mined a dataset of 259,511 SARS-CoV-2-infected individuals 0-105 years old in which virus RNA was quantified in nasopharyngeal swabs (viral load) using PCR at first healthcare contact. Subjects were stratified by vaccination and pandemic variant wave. Severity was assessed by hospital admission or death. Multivariable models analysed the influence of age on viral load, and viral load on severity.

Results: Among non-vaccinated (n = 140,905), viral loads of SARS-CoV-2 were lowest in children 1-9 years old and highest in infants (<1 year old) and in subjects 70-105 years, with similar results across pandemic waves and in vaccinated individuals. High viral load (≥9log₁₀viral RNA copies/swab) associated with elevated risk of hospital admission across age groups. In adults (20-69 years old), mortality was largely confined to those with high viral load (odds ratio [OR] 5.3, 95%CI 3.6-7.3). Among subjects ≥ 70 years old, deaths occurred across viral loads but were more frequent at high viral loads (OR 2.2, 95% CI 1.9-2.6). High viral load associated with hospitalisation and mortality also in vaccinated individuals (n = 118,606).

Conclusions: This study identified high viral load at first sampling as a predictor of severe infection and/or death across age groups of SARS-CoV-2-infected patients.