ABSTRACT
Background This study was planned to investigate how the positivization time of a SARS-CoV-2 rapid antigen self-test may correlate with SARS-CoV-2 nucleocapsid (N) antigen concentration measured with a quantitative laboratory-based immunoassay. Methods Paired nasopharyngeal (healthcare-collected) and nasal (self-collected) samples were taken from patients undergoing routine SARS-CoV-2 testing. The concentration of SARS-CoV-2 antigen nucleocapsid (N) was assayed with Liaison SARS-CoV-2 Antigen test, whilst the time of positivization of COVID-VIRO ALL rapid diagnostic test (RDT) was concomitantly measured and then compared SARS-CoV-2 viral load measured with Liaison SARS-CoV-2 Antigen test and expressed as Median Tissue Culture Infectious Dose (TCID50)/mL. Results The study sample consisted of 32 paired specimens which tested positive with COVID-VIRO ALL IN RDT and had SARS-CoV-2 N protein concentration measured with Liaison SARS-CoV-2 Antigen test. A highly significant correlation was found between SARS-CoV-2 viral antigen concentration and RDT positivization time (r=-0.64;95%CI, -0.81 to -0.38;p<0.001). At the >1500 TCID50/mL threshold of the Liaison SARS-CoV-2 Antigen test, the positivization time of the COVID-VIRO ALL IN RDT displayed high accuracy (93.7%). A positivization time <42 sec enabled to identify patients with high SARS-CoV-2 antigen concentration (i.e., >1500 TCID50/mL) with 91.3% negative and 100% positive predictive values. Conclusion Self-testing using COVID-VIRO ALL IN RDT could be reliably used for garnering valuable information on the actual SARS-CoV-2 viral antigen concentration in respiratory samples.
ABSTRACT
Background In this serosurveillance study, we investigated the variation of total anti-SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) antibodies in healthcare workers receiving primary BNT162b2 vaccination and homologous booster. Methods A total number of 524 subjects (median age, 46 years;65.3% females), were studied. All received primary BNT162b2 vaccination (two doses) and homologous booster (one dose) >8 months after completing the primary cycle. Blood samples were collected before the first and second vaccine doses, at 1, 3 and 6 months after the second dose, as well as before and 1 month after booster. Total anti-SARS-CoV-2 neutralizing antibodies were assayed with Roche Elecsys Anti-SARS-CoV-2 S chemiluminescent immunoassay. Results Overall, 65.1% subjects were baseline (i.e., pre-vaccination) SARS-CoV-2 seronegative and always tested SARS-CoV-2 negative (“N/N”), 16.2% were baseline SARS-CoV-2 seronegative but tested SARS-CoV-2 positive after receiving the vaccine booster dose (“N/P”), whilst 18.7% were baseline SARS-CoV-2 seropositive and always tested SARS-CoV-2 negative afterwards (“P/N”). All groups displayed a similar trend of total anti-SARS-CoV-2 S antibodies throughout the study period, though the P/N cohort exhibited higher values compared to the other two groups until receiving the booster, after which the levels become similar in all cohorts. Significant differences in total anti-SARS-CoV-2 S antibodies values were not found between N/N and N/P groups, neither 1 month after booster. The rate of subjects with protective antibodies values become 100% in all groups after booster. Conclusions Although baseline seropositivity is associated with more pronounced humoral immune response following primary vaccination compared to never infected subjects, SARS-CoV-2 infection after booster does not significantly foster antibody titers.