Diagnostic usefulness of subgenomic RNA detection of viable SARS-CoV-2 in patients with COVID-19.

OBJECTIVES: The development of a rapid diagnostic test for viable SARS-CoV-2 is important for infection control. Real-time RT-PCR assays detect non-viable virus, and cell culture differentiates viable virus but it takes several weeks and is labour-intensive. Subgenomic RNAs may reflect replication-competent virus. We therefore evaluated the usefulness of subgenomic RNAs for diagnosing viable SARS-CoV-2 in patients with COVID-19. METHODS: Patients with various severities of confirmed COVID-19 were enrolled at a tertiary hospital between February and December 2020. RT-PCR assay results for genomic and subgenomic RNA of SARS-CoV-2 from nasopharyngeal swab, sputum and saliva specimens were compared with cell culture results. RESULTS: A total 189 specimens from 20 COVID-19 patients were tested in genomic and subgenomic PCR assays and cultured on Vero cells. Of these 189 samples, 62 (33%) gave positive culture results, 93 (49%) negative results and the remaining 34 (18%) indeterminate results. Compared with cell culture results, the sensitivities of genomic RNA and subgenomic RNA of the N and S genes were comparable at 100%, but the specificity of subgenomic RNA (N, 65% and S, 68%) was higher than that of genomic RNA (N, 23% and S, 17%, p < 0.001). The mean durations of positive culture and subgenomic RNA were 11.39 ± 10.34 and 13.75 ± 11.22 days after symptom onset (p 0.437), respectively, while that of genomic RNA was 22.85 ± 11.83 days after symptom onset (p < 0.001). DISCUSSION: Our comparison of subgenomic RNA detection with symptom duration and SARS-CoV-2 culture positivity provides a significant advancement on the transmissibility-based approach beyond the detection of SARS-CoV-2 genomic RNA, and warrants further studies on the development of better diagnostic strategy.

Dynamics of Viral Shedding and Symptoms in Patients with Asymptomatic or Mild COVID-19.

We conducted a prospective cohort study at a community facility designated for the isolation of individuals with asymptomatic or mild COVID-19 between 10 January and 22 February 2021 to investigate the relationship of viral shedding with symptom changes of COVID-19. In total, 89 COVID-19 adult patients (12 asymptomatic, 16 presymptomatic, 61 symptomatic) were enrolled. Symptom scores, the genomic RNA and subgenomic RNA of SARS-CoV-2 from saliva samples with a cell culture were measured. Asymptomatic COVID-19 patients had a similar viral load to symptomatic patients during the early course of the disease, but exhibited a rapid decrease in viral load with the loss of infectivity. Subgenomic RNA and viable virus by cell culture in asymptomatic patients were detected only until 3 days after diagnosis, and the positivity of the subgenomic RNA and cell culture in symptomatic patients gradually decreased in both from 40% in the early disease course to 13% at 10 days and 4% at 8 days after the symptom onset, respectively. In conclusion, symptomatic patients have a high infectivity with high symptom scores during the early disease course and gradually lose infectivity depending on the symptom. Conversely, asymptomatic patients exhibit a rapid decrease in viral load with the loss of infectivity, despite a similar viral load during the early disease course.

Correlation between Reactogenicity and Immunogenicity after the ChAdOx1 nCoV-19 and BNT162b2 mRNA Vaccination.

Correlation between vaccine reactogenicity and immunogenicity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is unclear. Thus, we investigated to determine whether the reactogenicity after coronavirus disease 2019 vaccination is associated with antibody (Ab) titers and T cell responses. This study was prospective cohort study done with 131 healthcare workers at tertiary center in Seoul, South Korea. The degrees of the local reactions after the 1st and 2nd doses of ChAdOx1 nCov-19 (ChAdOx1) vaccination were significantly associated with the S1-specific IgG Ab titers (p=0.003 and 0.01, respectively) and neutralizing Ab (p=0.04 and 0.10, respectively) in age- and sex-adjusted multivariate analysis, whereas those after the BNT162b2 vaccination did not show significant associations. T cell responses did not show significant associations with the degree of reactogenicity after the ChAdOx1 vaccination or the BNT162b2 vaccination. Thus, high degree of local reactogenicity after the ChAdOx1 vaccine may be used as an indicator of strong humoral immune responses against SARS-CoV-2.