A Single Drop of Fingerstick Blood for Quantitative Antibody Response Evaluation After SARS-CoV-2 Vaccination (preprint)

Among several COVID vaccines that have been approved, the Moderna and Pfizer-BioNTech vaccines are mRNA vaccines that are safe and highly effective at preventing COVID-19 illness. Studies have demonstrated that neutralizing antibody responses elicited by these vaccines correlate strongly with antibodies measured by immunoassays such as ELISA. To monitor the antibody level duration of vaccine-induced immune responses in vaccinated population, cost-effective and easily implementable antibody testing methodologies are urgently needed. In this study, we evaluated the feasibility of using a single drop of fingerstick blood collected with flocked swabs for a high-throughput and quantitative anti-SARS-CoV-2 spike (S1) IgG antibody immunoassay. A total of 50 voluntary subjects participated and donated fingerstick blood samples before and after receiving the Moderna mRNA vaccine. Among all individuals tested, no anti-SARS-CoV-2 S1 IgG antibody was detected before vaccination and on day 7 after receiving the first vaccine dose. On day 14 after the first dose, a significant amount of anti-SARS-CoV-2 S1 IgG antibody was detected in all participants samples. By the end the third week from the first dose, the median anti-SARS-CoV-2 S1 IgG concentration increased to 44.9 ug/mL. No anti-SARS-CoV-2 nucleocapsid (N) protein IgG antibody was detected in any of the participants during the study period, indicating that the anti-SARS-CoV-2 S1 IgG assay is specific for the mRNA vaccine induced antibodies. Comaprison of venous blood plasma and fingerstick blood for anti-SARS-CoV-2 S1 IgG shown a higher correlation. Furthermore, the fingerstick blood dried swab samples are stable for at least 4 days. In summary, we demonstrated that a single drop of fingerstick blood collected with flocked swab can be used for quantitative detection and monitoring of anti-SARS-CoV-2 spike IgG responses after receiving COVID-19 vaccination. This testing platform does not require venous blood draw and can be easily implemented for large scale antibody testing in vaccinated populations.

Saliva as a testing specimen with or without pooling for SARS-CoV-2 detection by multiplex RT-PCR test (preprint)

BackgroundSensitive and high throughput molecular detection assays are essential during the coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The vast majority of the SARS-CoV-2 molecular assays use nasopharyngeal swab (NPS) or oropharyngeal swab (OPS) specimens collected from suspected individuals. However, using NPS or OPS as specimens has apparent drawbacks, e.g. the collection procedures for NPS or OPS specimens can be uncomfortable to some people and may cause sneezing and coughing which in turn generate droplets and/or aerosol particles that are of risk to healthcare workers, requiring heavy use of personal protective equipment. There have been recent studies indicating that self-collected saliva specimens can be used for molecular detection of SARS-CoV-2 and provides more comfort and ease of use for the patient. Here we report the performance of QuantiVirus SARS-CoV-2 multiplex test using saliva as the testing specimens with or without pooling. MethodsDevelopment and validation studies were conducted following FDA-EUA and molecular assay validation guidelines. Using SeraCare Accuplex SARS-CoV-2 reference panel, the limit of detection (LOD) and clinical evaluation studies were performed with the QuantiVirus SARS-CoV-2 multiplex test. For clinical evaluation, 85 known positive and 90 known negative clinical NPS samples were tested. Additionally, twenty paired NPS and saliva samples collected from recovering COVID-19 patients were tested and the results were further compared to that of the Abbott m2000 SARS-CoV-2 PCR assay. Results of community collected 389 saliva samples for COVID-19 screening by QuantiVirus SARS-CoV-2 multiplex test were also obtained and analyzed. Moreover, saliva pooling with 6 and 12 samples together were also evaluated. ResultsThe LOD for the QuantiVirus SARS-CoV-2 multiplex test was confirmed to be 100-200 copies/mL. The clinical evaluation using contrived saliva samples indicated that the positive percentage agreement (PPA) of the QuantiVirus SARS-CoV-2 multiplex test is 100% at 1xLOD, 1.5xLOD and 2.5xLOD. No cross-reactivity was observed for the QuantiVirus SARS-CoV-2 multiplex test with common respiratory pathogens. Testing of clinical samples showed a positive percentage agreement (PPA) of 100% (95% CI: 94.6% to 100%) and a negative percentage agreement (NPA) of 98.9% (95% CI: 93.1% to 99.9%). QuantiVirus SARS CoV-2 multiplex test had 80% concordance rate and no significant difference (p=0.13) in paired saliva and NPS specimens by Wilcoxon matched pairs signed rank test. Positive test rate was 1.79% for 389 saliva specimens collected from the communities for COVID-19 screening. Preliminary data showed that saliva sample pooling up to 6 samples for SARS-CoV-2 detection is feasible (sensitivity 94.8% and specificity 100%). ConclusionThe studies demonstrated that the QuantiVirus SARS-CoV-2 multiplex test has a LOD of 200 copies/mL in contrived saliva samples. The clinical performance of saliva-based testing is comparable to that of NPS-based testing. Pooling of saliva specimens for SARS-CoV-2 detection is feasible. Saliva based and high-throughput QuantiVirusSARS-CoV-2 multiplex test offers a highly desirable test during the ongoing COVID-19 pandemic.