Viral RNA Load in Symptomatic and Asymptomatic COVID-19 Omicron Variant-Positive Patients

Abstract

Objectives. Viral load is important when evaluating viral transmission potential, involving the use of a polymerase chain reaction (PCR) cycle threshold (Ct) value. We aimed to analyze the PCR Ct values of respiratory tract samples taken from patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant strains to evaluate these strains’ viral dynamics. Methods. This study comprised 361 patients. The Ct values of SARS-CoV-2-related respiratory samples were compared between symptomatic and asymptomatic patients. Results. The median (25th percentile and 75th percentile) nasopharynx and oropharynx SARS-CoV-2 Ct values were 30.5 (24.5–35.0) and 34.5 (30.0–37.0) in the symptomatic group, respectively, and 27.8 (23.4–34.5) and 33.5 (26.0–35.0) in the asymptomatic group, respectively, without significance. In the symptomatic group, subgroup analyses according to age showed the mean nasal Ct value for patients aged >18 years was 29.0 (23.5–34.5), which was significantly lower than that of patients aged 0–4 years and 5–13 years (36.0 (30.5–38.0) and 34.5 (31.0–39.0), respectively). The nasal Ct value for asymptomatic patients aged >18 years was 25.5 (20.9–28.4), which was significantly lower than of patients aged 5–13 years (34.5 (25.6–36.4)). Conclusion. Our findings suggest that the viral loads of asymptomatic and symptomatic patients did not differ significantly. However, adults infected with SARS-CoV-2 had higher nasal viral loads that those of young children.

Viral load dynamics in asymptomatic and symptomatic patients during Omicron BA.2 outbreak in Shanghai, China, 2022: a longitudinal cohort study

“…Additionally, the viral load dynamic for the overall study population was relatively low and shedding quickly due to the large proportion of asymptomatic and mild-moderate cases with lower viral loads. Compared to the limited results on Omicron, our findings regarding the initial Ct value were similar to observations of adolescent children 24,25 , adults 26 and elderly patients 27 . Few studies have reported the severity-specific Omicron viral load, and the participants in these studies had different compositions of clinical severity 11,15 .…”

Border Control for Infectious Respiratory Disease Pandemics: A Modelling Study for H1N1 and Four Strains of SARS-CoV-2

“…The hyperparameters for omicron were obtained by combining the data for the delta (vaccinated) variant with data from Young et al [17] that compared delta and omicron viral load trajectories in vaccine breakthrough infections. The same parameter distributions were used for both symptomatic and asymptomatic travellers, in accordance with evidence that symptomatic and asymptomatic COVID-19 infections have similar viral loads [18,19]. The distribution for influenza A-H1N1 was derived from a study of experimental infections by Canini et al [20].…”

The asymptomatic proportion of SARS-CoV-2 Omicron-variant infections in households: A systematic review

“…Studies have shown that the viral load in the upper respiratory tracts of asymptomatic infected persons is comparable to that of symptomatic individuals, thus these individuals potentially contribute to onward transmission. (5-7) Asymptomatic individuals may be less likely to be indicated for or willing to test for infection, and rapid antigen tests (RATs) have been shown to have reduced diagnostic sensitivity in asymptomatic persons. (8-10) Further, individuals with asymptomatic infections may be less likely to practice social or physical distancing measures — due to not knowing they are infected and potentially infectious — and thus may contribute to the spread of infection in the general population.…”