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Background: We studied humoral and cellular responses against SARS-CoV-2 longitudinally in a homogeneous population of healthy young/middle-aged men of South Asian ethnicity with mild COVID-19. Met...

Background: We studied humoral and cellular responses against SARS-CoV-2 longitudinally in a homogeneous population of healthy young/middle-aged men of South Asian ethnicity with mild COVID-19. Methods: In total, we recruited 994 men (median age: 34 years) post-COVID-19 diagnosis. Repeated cross-sectional surveys were conducted between May 2020 and January 2021 at six time points – day 28 (n = 327), day 80 (n = 202), day 105 (n = 294), day 140 (n = 172), day 180 (n = 758), and day 280 (n = 311). Three commercial assays were used to detect anti-nucleoprotein (NP) and neutralizing antibodies. T cell response specific for Spike, Membrane and NP SARS-CoV-2 proteins was tested in 85 patients at day 105, 180, and 280. Results: All serological tests displayed different kinetics of progressive antibody reduction while the frequency of T cells specific for different structural SARS-CoV-2 proteins was stable over time. Both showed a marked heterogeneity of magnitude among the studied cohort. Comparatively, cellular responses lasted longer than humoral responses and were still detectable nine months after infection in the individuals who lost antibody detection. Correlation between T cell frequencies and all antibodies was lost over time. Conclusion: Humoral and cellular immunity against SARS-CoV-2 is induced with differing kinetics of persistence in those with mild disease. The magnitude of T cells and antibodies is highly heterogeneous in a homogeneous study population. These observations have implications for COVID-19 surveillance, vaccination strategies, and post-pandemic planning.

Background As new high-sensitivity (hs) cardiac troponin (cTn) assays are introduced decision limits, based on the 99th percentile upper reference limit (99 percentile URL), for each method must be determined and from a sufficiently large cohort to mitigate against distortionary effects of high-end outliers. There is a paucity of studies with large multi-ethnic cohorts. Methods We determined the 99 percentile URL in 1120 (mean age: 50.4 ± 8.2 y) apparently healthy (no history of diabetes, hypertension, heart, lung, or renal disease) Asians (597 men aged 35–65 y, 523 women aged 40–65 y) in a pre-market hs-cTnI assay (Abbott Diagnostics). Results Hs-cTnI performance was: limit of blank - 0.6 ng/l, limit of detection (LoD) - 1.5 ng/l; cTnI inter-assay coefficient of variation of 20% and 10% were 1.5 and 6.0 ng/l respectively. Hs-cTnI concentrations (range: 0–49.3 ng/l) were detectable (> assay LoD) in 92.3% of participants, and higher in men and individuals > 50 y. All-subject, male, and female 99 percentile URL (90% CI) were 25.6 (19.6–32.6), 32.7 (21.1–47.9) and 17.9 (10.7–26.3) ng/l respectively. Conclusion This hs-cTnI assay exhibits hs performance besides gender and age differences. The all-subject 99 percentile URL values are similar to those reported from some groups but not in others. Users need to establish their own decision limits.