Ancestral SARS-CoV-2 and Omicron BA.5-specific neutralizing antibody and T-cell responses after Omicron bivalent booster vaccination in previously infected and infection-naive individuals.

Coronavirus disease-2019 (COVID-19) bivalent ancestral/Omicron messenger RNA (mRNA) booster vaccinations became available to boost and expand the immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron infections. In a prospective cohort study including 59 healthcare workers, we assessed SARS-CoV-2 ancestral and Omicron BA.5-specific neutralizing antibody and T-cell responses in previously infected and infection-naive individuals. Also, we assessed the effect of an ancestral/Omicron BA.1 bivalent mRNA booster vaccination on these immune responses. 10 months after previous monovalent mRNA vaccinations, ancestral SARS-CoV-2 S1-specific T-cell and anti-RBD IgG responses remained detectable in most individuals and a previous SARS-CoV-2 infection was associated with increased T-cell responses. T-cell responses, anti-RBD IgG, and Omicron BA.5 neutralization activity increased after receiving an ancestral/Omicron BA.1 bivalent booster mRNA vaccination. An Omicron BA.5 infection in addition to bivalent vaccination, led to a higher ratio of Omicron BA.5 to ancestral strain neutralization activity compared to no bivalent vaccination and no recent SARS-CoV-2 infection. In conclusion, SARS-CoV-2 T-cell and antibody responses persist for up to 10 months after a monovalent booster mRNA vaccination. An ancestral/Omicron BA.1 bivalent booster mRNA vaccination increases these immune responses and also induces Omicron BA.5 cross-neutralization antibody activity. Finally, our data indicate that hybrid immunity is associated with improved preservation of T-cell immunity.

Clinical evaluation of rapid point-of-care antigen tests for diagnosis of SARS-CoV-2 infection.

The RT-qPCR in respiratory specimens is the gold standard for diagnosing acute COVID-19 infections. However, this test takes considerable time before test results become available, thereby delaying patients from being diagnosed, treated, and isolated immediately. Rapid antigen tests could overcome this problem. In the first study, clinical performances of five rapid antigen tests were compared to RT-qPCR in upper respiratory specimens from 40 patients with positive and 40 with negative RTq-PCR results. In the second study, the rapid antigen test with one of the best test characteristics (Romed) was evaluated in a large prospective collection of upper respiratory specimens from 900 different COVID-19-suspected patients (300 emergency room patients, 300 nursing home patients, and 300 health care workers). Test specificities ranged from 87.5 to 100.0%, and test sensitivities from 55.0 to 80.0%. The clinical specificity of the Romed test was 99.8% (95% CI 98.9-100). Overall clinical sensitivity in the study population was 73.3% (95% CI 67.9-78.2), whereas sensitivity in the different patient groups varied from 65.3 to 86.7%. Sensitivity was 83.0 to 86.7% in patients with short duration of symptoms. In a population with a COVID-19 prevalence of 1%, the negative predictive value in all patients was 99.7%. There is a large variability in diagnostic performance between rapid antigen tests. The Romed rapid antigen test showed a good clinical performance in patients with high viral loads (RT-qPCR cycle threshold ≤30), which makes this antigen test suitable for rapid identification of COVID-19-infected health care workers and patients.

Evaluation of a New Standardized Nasal Sampling Method for Detection of SARS-CoV-2 RNA via RT-PCR.

The aim of this study was to compare the diagnostic accuracy of nasal sampling using a novel anterior nasal swab (ANS) (Rhinoswab) versus combined oro-nasopharyngeal (OP/NP) sampling in COVID-19 suspected patients. This prospective observational study was performed from 11 November to 2 December 2021 (part 1), and from 16 January to 22 February 2022 (part 2). Adult patients who attended the emergency room with suspected COVID-19 were asked to participate. One ANS and one OP/NP sample were consecutively collected, and both were analyzed via reverse transcription polymerase chain reaction (RT-PCR). The result of the OP/NP sample was considered to be the reference standard. A total of 412 patients were included, of whom 171 (41.5%) had a positive RT-PCR of the OP/NP swab, whereas 139 (33.7%) were positive on the ANS sample. The overall diagnostic accuracy for ANS sampling in terms of sensitivity, specificity, positive predictive value, and negative predictive value was 80.7% (95% CI 73.8-86.2), 99.6% (95% CI 97.3-100), 99.3% (95% CI 95.5-100), and 87.9% (95% CI 83.3-91.4), respectively. In conclusion, ANS sampling with the Rhinoswab identified 80.7% of all presented COVID-19 patients in an emergency department. Future studies should investigate if nasal Rhinoswab self-sampling is suitable for reliable diagnosis of COVID-19 in an outpatient setting.

SARS-CoV-2-specific T cell responses: a comparative analysis between QuantiFERON SARS-CoV-2, T-SPOT.COVID, and an in-house Omicron ELISpot.

BACKGROUND: T cell immunity plays a pivotal role in mitigating the severity of coronavirus disease 2019 (COVID-19). Therefore, reliable functional T cell assays are required to evaluate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T cell immunity in specific patient populations. METHODS: We recruited a cohort of 23 healthcare workers who received their bivalent Omicron BA.1 / ancestral mRNA booster vaccination or were infected with the Omicron variant at a median of 144 days and 227 days before blood collection, respectively. In this cohort, we compared the performances of two widely utilized commercial SARS-CoV-2 interferon-gamma release assays (IGRAs), i.e., QuantiFERON SARS-CoV-2 and T-SPOT.COVID, and an in-house designed Omicron enzyme-linked immunospot (ELISpot). RESULTS: The QuantiFERON SARS-CoV-2 and T-SPOT.COVID assays detected SARS-CoV-2 spike-specific T cells in 34.8 % and 21.7 % of participants, respectively. Moreover, our in-house designed ELISpot that included Omicron BA.4 and BA.5 full-spike peptides detected T cell responses in 47.8 % of participants and was strongly associated with the T-SPOT.COVID. CONCLUSION: The evaluation of SARS-CoV-2 T cell immunity using commercially accessible assays may yield disparate outcomes as results from different assays are not directly comparable. A specific Omicron ELISpot should be considered to assess Omicron-specific T cell immunity.

Development of an in-house SARS-CoV-2 interferon-gamma ELISpot and plate reader-free spot detection method.

Coronavirus disease 2019 (COVID-19) vaccination programs rolled out in an attempt to stop the COVID-19 pandemic. Besides neutralising antibodies, effective T cell responses are also crucial for protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and COVID-19 disease severity. To assess SARS-CoV-2-specific T cell immunity, we developed an interferon-gamma (IFN-γ) enzyme-linked immunospot (ELISpot) that can be deployed in research and diagnostic settings. We optimised our ELISpot by testing multiple antigen concentrations to stimulate peripheral blood mononuclear cells of SARS-CoV-2-unexposed, COVID-19 convalescent and COVID-19 vaccinated volunteers. Also, we developed an ELISpot plate reader-free method to detect and quantify spots, which we compared to manual spot counting and automated analysis by an ELISpot plate reader. We observed strong SARS-CoV-2-reactive T cell responses in COVID-19 convalescent, and COVID-19 vaccinated volunteers but absent or only weak responses in unexposed volunteers. Overall, antigens with concentrations from 0.1 to 5.0 µg/mL per peptide elicited similar T cell responses. Also, our plate reader-free detection method reliably detected and quantified SARS-CoV-2-specific T cells, demonstrated by an excellent reliability when compared to manual analysis and automated analysis by an ELISpot plate reader.

SARS-CoV-2 antibody and T cell responses one year after COVID-19 and the booster effect of vaccination: A prospective cohort study.

OBJECTIVES: First, to describe SARS-CoV-2 T cell and antibody responses in a prospective cohort of healthcare workers that suffered from mild to moderate COVID-19 approximately one year ago. Second, to assess COVID-19 vaccine-induced immune responses in these prior-infected individuals. METHODS: SARS-CoV-2-specific T cell and anti-SARS-CoV-2-Spike-RBD immunoglobulin G (IgG) responses in blood were determined before COVID-19 vaccination with mRNA-1273, BNT162b2, Ad26.CoV2-S or ChAdOx1-S, two weeks after first vaccination, and after second vaccination. RESULTS: 55 prior SARS-CoV-2 infected and seroconverted individuals were included. S1-specific T cell responses and anti-RBD IgG were detectable one year post SARS-CoV-2 infection: 24 spot-forming cells per 106 peripheral blood mononuclear cells (SFCs/106 PBMCs) after S1 stimulation and anti-RBD IgG concentration of 74 (IQR 36-158) IU/mL. Responses after the first and second vaccination were comparable with S1-specfic T cell responses of 198 (IQR 137-359) and 180 (IQR 103-347) SFCs/106 PBMCs, and IgG concentrations of 6792 (IQR 3386-15,180) and 6326 (IQR 2336-13,440) IU/mL, respectively. These responses retained up to four months after vaccination. CONCLUSIONS: Both T cell and IgG responses against SARS-CoV-2 persist for up to one year after COVID-19. A second COVID-19 vaccination in prior-infected individuals did not further increase immune responses in comparison to one vaccination.

Dynamics of Antibody and T Cell Immunity against SARS-CoV-2 Variants of Concern and the Impact of Booster Vaccinations in Previously Infected and Infection-Naïve Individuals.

Despite previous coronavirus disease 2019 (COVID-19) vaccinations and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, SARS-CoV-2 still causes a substantial number of infections due to the waning of immunity and the emergence of new variants. Here, we assessed the SARS-CoV-2 spike subunit 1 (S1)-specific T cell responses, anti-SARS-CoV-2 receptor-binding domain (RBD) IgG serum concentrations, and the neutralizing activity of serum antibodies before and one, four, and seven months after the BNT162b2 or mRNA-1273 booster vaccination in a cohort of previously infected and infection-naïve healthcare workers (HCWs). Additionally, we assessed T cell responses against the spike protein of the SARS-CoV-2 Delta, Omicron BA.1 and BA.2 variants of concern (VOC). We found that S1-specific T cell responses, anti-RBD IgG concentrations, and neutralizing activity significantly increased one month after booster vaccination. Four months after booster vaccination, T cell and antibody responses significantly decreased but levels remained steady thereafter until seven months after booster vaccination. After a similar number of vaccinations, previously infected individuals had significantly higher S1-specific T cell, anti-RBD IgG, and neutralizing IgG responses than infection-naïve HCWs. Strikingly, we observed overall cross-reactive T cell responses against different SARS-CoV-2 VOC in both previously infected and infection-naïve HCWs. In summary, COVID-19 booster vaccinations induce strong T cell and neutralizing antibody responses and the presence of T cell responses against SARS-CoV-2 VOC suggest that vaccine-induced T cell immunity offers cross-reactive protection against different VOC.

Rapid screening method for the detection of SARS-CoV-2 variants of concern.

BACKGROUND: Comprehensive and up-to-date monitoring of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOC) is crucial as these are characterized by their increased transmissibility, immune evasion and virulence. OBJECTIVES: To describe the wide-scale implementation of a reverse transcriptase polymerase chain reaction (RT-PCR) multiple variants assay with melting curve analysis as a routine procedure. STUDY DESIGN: We prospectively performed multiple variants RT-PCR on consecutive SARS-CoV-2 RT-PCR positive samples from patients, healthcare workers and nursing home residents from our hospital catchment area. This technique was implemented in our automated Roche FLOW system with a turn-around time of 6 h. RESULTS: Between February 1 and May 2, 2021, 989 samples were tested by the variant RT-PCR. Our method was validated by comparison of variant RT-PCR to whole genome sequencing testing. We observed an increase over time in the proportion of UK variant that became the dominant variant, and the concurrent emergence of the South-African and Brazilian variants. Prompt public health responses for infection control were possible because of this rapid screening method, resulting in early detection and reduction of unnoticed spread of VOC as early as possible. CONCLUSION: A variant RT-PCR with additional melting curve analyses is a feasible, rapid and efficient screening strategy that can be implemented in routine microbiological laboratories.

SARS-CoV-2 antibody response dynamics and heterogeneous diagnostic performance of four serological tests and a neutralization test in symptomatic healthcare workers with non-severe COVID-19.

BACKGROUND: Most COVID-19 patients experience non-severe illness. The presence of SARS-CoV-2 antibodies suggest possible protection against re-infections in prior SARS-CoV-2 infected individuals. OBJECTIVES: The aims of this prospective observational study were to longitudinally assess the antibody response during the first 4-6 months after polymerase chain reaction (PCR) confirmed SARS-CoV-2 infection, and to study the diagnostic performance of four different enzyme-linked immunosorbent assays (ELISAs) and a surrogate virus neutralization test (sVNT) in symptomatic healthcare workers (HCWs) with non-severe COVID-19. STUDY DESIGN: HCWs in a teaching hospital were included between March 8 and June 15, 2020, when they had a PCR-confirmed SARS-CoV-2 infection in the past 3 months. The performances of four ELISAs (Wantai, Bio-Rad Platelia, BioTrading Immy clarus, and Euroimmun) were evaluated in serum samples obtained at the moment of study inclusion and subsequently at 1, 2 and 3 months thereafter. Furthermore, in the last available serum sample sVNT by GenScript was performed. RESULTS: 309 samples from 80 positive HCWs were included of whom 70 (88%) were SARS-CoV-2 seropositive. The detection rates of SARS-CoV-2 antibodies by the different ELISAs were heterogenous ranging from 64% for the Euroimmun ELISA to 88% for the Wantai ELISA. The Wantai ELISA had the highest and almost perfect agreement with sVNT (96%, Cohen's kappa 0.83). CONCLUSION: SARS-CoV-2 (neutralizing) antibodies were detectable in most symptomatic individuals with non-severe COVID-19. The presence of antibodies remained stable up to six months after initial infection. There is large variability in diagnostic test performance between ELISA tests.