Performances of Dried Blood Spots and Point-of-Care Devices to Identify Virological Failure in HIV-Infected Patients: A Systematic Review and Meta-Analysis.

To broaden access to HIV viral load monitoring (VLM), the use of blood samples from dried blood spots (DBS) or point-of-care (POC) devices, could be of great help in settings where plasma is not easily accessible. The variety of assays available makes the choice complex. This systematic review and meta-analysis aims to estimate the sensitivity and specificity of DBS and POC devices to identify patients in virological failure using World Health Organization (WHO) recommendations (viral load ≥1000 copies/mL), compared with plasma, for the assays currently available. Four databases were searched for articles, and two reviewers independently identified articles reporting sensitivity and specificity of DBS and/or POC to identify patients in virological failure. We excluded articles that used other thresholds as well as articles with a total number of participants below 50 to avoid reporting bias. Heterogeneity and factors associated with assays' performances were assessed by I2 statistics and metaregression. The protocol of this review follows the PRISMA guidelines. Out of 941 articles, 47 were included: 32 DBS evaluations and 16 POC evaluations. Overall, when using DBS, the Abbott RT HIV-1, Roche CAP-CTM, NucliSENS BioMerieux and Aptima assays presented sensitivity and specificity exceeding 85%, but reported results were highly heterogeneous. Factors associated with better performances were high volume of blood and the use of the same assay for DBS and plasma VLM. Regarding the POC devices, SAMBA I, SAMBA II, and GeneXpert devices presented high sensitivity and specificity exceeding 90%, with less heterogeneity. DBS is suitable VLM, but performances can vary greatly depending on the protocols, and should be performed in trained centers. POC is suitable for VLM with less risk of heterogeneity but is more intensive in costs and logistics.

Dried blood spot eluates are suitable for testing of SARS-CoV-2 IgG antibodies targeting Spike protein 1 and Nucleocapsid protein.

Dried blood spots (DBS) provide easy handling and are thus a beneficial tool for data collection, e.g. for epidemiological studies. The suitability of DBS for the assessment of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was analyzed with regards to the use in future studies addressing seroprevalence in the population. 121 volunteers gave a venous blood sample and capillary blood samples on two DBS cards (PerkinElmer and Ahlstrom-Munksjö) via self-sampling under supervision. All samples were analyzed using the Anti-SARS-CoV-2 ELISA (IgG) and the Anti-SARS-CoV-2 NCP ELISA (IgG) from EUROIMMUN performed on the EUROIMMUN EUROLabWorkstation ELISA. Correlation coefficients between ELISA results based on the different sampling methods were calculated. Results of DBS analysis for SARS-CoV-2 IgG S1 and NCP highly correlated with the serum values (r = 0.96). In addition, the calculation of the phi coefficient showed no significant difference between the qualitative results of both sampling methods (rφ = 0.98-1.0). Further analysis of DBS eluates after prolonged storage of 6-8 h also showed a high correlation with serum results (r = 0.97 and r = 0.93, respectively). The study results indicate suitability of DBS for the analysis of antibodies against SARS-CoV-2 S1 and NCP. For DBS eluate, a stability of 6-8 h for measurement of SARS-CoV-2 antibodies can be assumed.

A pilot study: Validation of dried blood spots (DBS) to assess SARS-CoV2 IgG antibody immunoassays in underserved minority population.

Underserved, low-income, rural and certain migrant populations have greater risks and higher incidences of Coronavirus disease 2019 (COVID-19) than more privileged populations. Current in-person testing methods have limitations, namely exposure risk, a requirement of accessible transportation to healthcare facilities, and economic barriers. Dried blood spots (DBS) samples are widely used for diagnostics in many infectious diseases including Rabies, HIV, Ebola viruses and newborn screening. Our goal was to determine the accuracy and reliability of measuring COVID-19 IgG in DBS compared to paired plasma samples in a population with known infection status and then apply this method to screen an underserved minority population with high risk for COVID-9 infection (unvaccinated, pregnant, low income, Hispanic women). To optimize the assay, we tested 22 nonpregnant women, 12 with positive prior PCR testing for SARS-CoV2 infection and 10 with negative PCR results. After the assay was optimized, we tested the assay in a vulnerable population with a high risk for infection, who were 52 Hispanic pregnant women without prior PCR testing or vaccination. DBS assay results in both groups showed an agreement of 100% with paired plasma samples. The availability of a DBS assay could enable people who may not have access or transportation to healthcare facilities to use DBS as a COVID-19 testing vehicle.

Modified ARCHITECT® serologic assays enable plasma-level performance from dried blood spot samples.

Dried blood spots (DBSs) provide an alternative sample input for serologic testing. We evaluated DBSs for the ARCHITECT® hepatitis B surface antigen (HBsAg) NEXT, hepatitis B e-antigen (HBeAg), anti-hepatitis B core antigen (anti-HBc II), HIV antigen/antibody (Ag/Ab) Combo and AdviseDx SARS-CoV-2 IgG II assays. Assay performance with DBSs was assessed with or without assay modification and compared with on-market assay with plasma samples. DBS stability was also determined. HBsAg NEXT and HIV Ag/Ab Combo assays using DBSs showed sensitivity and specificity comparable to that of on-market assays. Modified HBeAg, anti-HBc II and SARS-CoV-2 IgG II DBS assays achieved performance comparable to on-market assays. Use of DBSs as input for high-throughput serologic assays is expected to have significant implications for improving population surveillance and increasing access to diagnostic testing.

Evaluation of serological assays for SARS-CoV-2 antibody testing from dried blood spots collected from cohorts with prior SARS-CoV-2 infection.

Background: Dried blood spot (DBS) specimens are a useful serosurveillance tool particularly in hard-to-reach populations but their application for detecting SARS-CoV-2 infection is poorly characterised. Objectives: To compare detection of naturally acquired SARS-CoV-2 antibodies in paired DBS and serum specimens using commercially available serological immunoassays. Study Design: Specimens were collected through St Vincent's Hospital observational post COVID-19 cohort study (ADAPT). Laboratory spotted DBS from venepuncture were initially tested on seven assays, a DBS validation completed on three with clinically collected fingerstick DBSs tested on one. Results: Sensitivity for Euroimmun nucleocapsid (NCP) IgG ELISA from laboratory spotted DBS (n=145), Euroimmun spike, IgG ELISA from laboratory spotted DBS (n=161), and Binding Site total antibody ELISA from clinically collected fingerstick DBS (n=391) was 100% (95% CI: 95.8-100%), 100% (95% CI: 95.8-100%) and 92.9% (95% CI: 89.5-95.5%), respectively. Specificity was 66.2% (95% CI: 53.6-77.0%), 96% (95% CI: 88.7-99.1%) and 98.8% (95% CI: 93.3-99.9%), respectively. All three assays' results displayed a strong positive correlation between DBS compared to paired serum. Conclusions: The Binding Site™ spike total antibody and Euroimmun™ spike IgG ELISAs provided good analytical performance, demonstrating that DBS specimens could facilitate specimen collection in the epidemiological surveillance of SARS-CoV-2 infection. This is highly applicable in populations and settings where venepuncture is problematic (including community based regional/remote settings, nursing homes, prisons, and schools).

Seroprevalence of SARS-CoV-2 antibodies in Italy in newborn dried blood spots.

OBEJCTIVES: Serosurveys can be used to monitor COVID-19 seroprevalence and conduct surveillance. Dried blood spot (DBS), used increasingly as a valuable sample to assay severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antibodies (Ab), has several advantages, particularly in infants, due to the limited amount of blood required and its utility in testing a large number of samples in a limited time-frame. We evaluated SARS-CoV-2 IgG Ab prevalence in newborn DBS in the Trentino region of Italy, during the time period January 2020 - December 2021. METHODS: Anti-SARS-CoV-2 IgG levels were determined in DBS by means of Anti-SARS-CoV-2 QuantiVac IgG ELISA assay (Euroimmun, Lubeck, Germany). RESULTS: Analyses included 2,400 DBS from newborns (54% M, 46% F), samples being collected 2-3 days after birth. The first DBS that tested positive for anti-SARS-CoV-2 IgG antibodies was found in March 2020 and, up to May 2020, only 4 positive results were detected overall. Starting from June 2020, the positivity thresholds increased according to the epidemiological waves of the COVID-19 pandemic in Italy, with a robust increment in the winters of 2020 and 2021. The percentage of positive DBS rose from 0 to 6% to 10-47%, in 2020 and 2021, respectively. CONCLUSIONS: This study demonstrates DBS is a suitable tool for both epidemiological purposes and surveillance in the SARS-CoV-2 pandemic, particularly in newborns and pregnant women, saving blood waste and sparing patients any discomfort.

Use of Self-Collected Dried Blood Spots and a Multiplex Microsphere Immunoassay to Measure IgG Antibody Response to COVID-19 Vaccines.

Serosurveys can determine the extent and spread of a pathogen in populations. However, collection of venous blood requires trained medical staff. Dried blood spots (DBS) are a suitable alternative because they can be self-collected and stored/shipped at room temperature. As COVID-19 vaccine deployment began in early 2021, we rapidly enrolled laboratory employees in a study to evaluate IgG antibody levels following vaccination. Participants received a DBS collection kit, self-collection instructions, and a brief questionnaire. Three DBS were collected by each of 168 participants pre- and/or postvaccination and tested with a multiplex microsphere immunoassay (MIA) that separately measures IgG antibodies to SARS-CoV-2 spike-S1 and nucleocapsid antigens. Most DBS (99.6%, 507/509) were suitable for testing. Participants with prior SARS-CoV-2 infection (n = 7) generated high S antibody levels after the first vaccine dose. Naïve individuals (n = 161) attained high S antibody levels after the second dose. Similar antibody levels were seen among those vaccinated with Moderna (n = 29) and Pfizer-BioNTech (n = 137). For those receiving either mRNA vaccine, local side effects were more common after the first vaccine dose, whereas systemic side effects were more common after the second dose. Individuals with the highest antibody levels in the week prior to the second vaccine dose experienced more side effects from the second dose. Our study demonstrated that combining self-collected DBS and a multiplex MIA is a convenient and effective way to assess antibody levels to vaccination and could easily be used for population serosurveys of SARS-CoV-2 or other emerging pathogens. IMPORTANCE Serosurveys are an essential tool for assessing immunity in a population (1, 2). However, common barriers to effective serosurveys, particularly during a pandemic, include high-costs, resources required to collect venous blood samples, lack of trained laboratory technicians, and time required to perform the assay. By utilizing self-collected dried blood spots (DBS) and our previously developed high-throughput microsphere immunoassay, we were able to significantly reduce many of these common challenges. Participants were asked to self-collect three DBS before and/or after they received their COVID-19 vaccines to measure antibody levels following vaccination. Participants successfully collected 507 DBS that were tested for IgG antibodies to the spike and nucleocapsid proteins of SARS-CoV-2. When used with self-collected DBS, our relatively low-cost assay significantly reduced common barriers to collecting serological data from a population and was able to effectively assess antibody response to vaccination.

Comparative performance data for multiplex SARS-CoV-2 serological assays from a large panel of dried blood spot specimens.

The extent of the COVID-19 pandemic will be better understood through serosurveys and SARS-CoV-2 antibody testing. Dried blood spot (DBS) samples will play a central role in large scale serosurveillance by simplifying biological specimen collection and transportation, especially in Canada. Direct comparative performance data on multiplex SARS-CoV-2 assays resulting from identical DBS samples are currently lacking. In our study, we aimed to provide performance data for the BioPlex 2200 SARS-CoV-2 IgG (Bio-Rad), V-PLEX SARS-CoV-2 Panel 2 IgG (MSD), and Elecsys Anti-SARS-CoV-2 (Roche) commercial assays, as well as for two highly scalable in-house assays (University of Ottawa and Mount Sinai Hospital protocols) to assess their suitability for DBS-based SARS-CoV-2 DBS serosurveillance. These assays were evaluated against identical panels of DBS samples collected from convalescent COVID-19 patients (n = 97) and individuals undergoing routine sexually transmitted and bloodborne infection (STBBI) testing prior to the COVID-19 pandemic (n = 90). Our findings suggest that several assays are suitable for serosurveillance (sensitivity >97% and specificity >98%). In contrast to other reports, we did not observe an improvement in performance using multiple antigen consensus-based rules to establish overall seropositivity. This may be due to our DBS panel which consisted of samples collected from convalescent COVID-19 patients with significant anti-spike, -receptor binding domain (RBD), and -nucleocapsid antibody titers. This study demonstrates that biological specimens collected as DBS coupled with one of several readily available assays are useful for large-scale COVID-19 serosurveillance.

Diagnostic performance of the SARS-CoV-2 S1RBD IgG ELISA (ImmunoDiagnostics) for the quantitative detection of SARS-CoV-2 antibodies on dried blood spots.

Dried Blood Spots (DBS) are broadly used in SARS-CoV-2 surveillance studies, reporting either the presence or absence of SARS-CoV-2 antibodies. However, quantitative follow-up has become increasingly important to monitor humoral vaccine responses. Therefore, we aimed to evaluate the performance of DBS for the detection of anti-spike SARS-CoV-2 antibody concentrations using a commercially available assay, reporting in a standardised unitage (International Units/mL; IU/mL). To assess the sensitivity and specificity of the ImmunoDiagnostics ELISA on serum and DBS for SARS-CoV-2 antibody detection, we analysed 72 paired DBS and serum samples. The SARS-CoV-2 S1 IgG ELISA kit (EUROIMMUN) on serum was used as the reference method. We performed a statistical assessment to optimise the cut-off value for DBS and serum and assessed the correlation between DBS and serum antibody concentrations. We found that anti-spike SARS-CoV-2 antibody concentrations detected in DBS are highly correlated to those detected in paired serum (Pearson correlation 0.98; p-value < 0.0001), allowing to assess serum antibody concentration using DBS. The optimal cut-off for antibody detection on DBS was found to be 26 IU/mL, with 98.1% sensitivity and 100% specificity. For serum, the optimal cut-off was 14 IU/mL, with 100% sensitivity and 100% specificity. Therefore, we conclude that the ImmunoDiagnostics ELISA kit has optimal performance in the detection of SARS-CoV-2 antibodies on both DBS and serum. This makes DBS ideal for large-scale follow-up of humoral SARS-CoV-2 immune responses, as it is an easy but valuable sampling method for quantification of SARS-CoV-2 antibodies, compared to serum.

Performance of Dried Blood Spot Samples in SARS-CoV-2 Serolomics.

Numerous sero-epidemiological studies have been initiated to investigate the spread and dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). To address the concomitant need for serological high-throughput assays, a bead-based multiplex serology assay, specific for SARS-CoV-2, had been developed. SARS-CoV-2 serolomics allows for measuring antibody responses to almost the entire SARS-CoV-2 proteome in up to 2000 serum samples per day. To enlarge the pool of eligible sample collection methods, we here test the compatibility of serolomics with dried blood spot (DBS)-derived eluates. Antibody levels of nine SARS-CoV-2 antigens, including the nucleocapsid (N) and receptor-binding domain of the spike protein (S1-RBD), were measured in 142 paired DBS and serum samples. The numeric correlation between the two sample types was high, with a Pearson's r of 0.88 for both S1-RBD and N and intraclass correlation coefficients of 0.93 and 0.92, respectively. Systematically reduced antibody levels in DBS eluates were compensated by lowering the cutoffs for seropositivity accordingly. This enabled the concordant classification of SARS-CoV-2 seropositivity, without loss in sensitivity. Antibody levels against accessory SARS-CoV-2 antigens also showed a high concordance, demonstrating that DBS-derived eluates are eligible for SARS-CoV-2 serolomics. DBS cards facilitate the collection of blood samples, as they obviate the need for medically trained personnel and can be shipped at room temperature. In combination with SARS-CoV-2 serolomics, DBS cards enable powerful sero-epidemiological studies, thus allowing for the monitoring of patients and epidemiological analyses in resource-poor settings.

Maternal SARS-CoV-2 sero-surveillance using newborn dried blood spot (DBS) screening specimens highlights extent of low vaccine uptake in pregnant women.

SARS-CoV-2 vaccine uptake in pregnant women is believed to be low and lags behind the general population contributing to increased hospital admissions, and poor maternal and fetal outcomes. However, there is a paucity of information on the SARS-CoV-2 serostatus of pregnant women to help inform policy planning and assess impact of interventions to improve vaccine uptake in this at-risk group. We analyzed 8,683 residual, anonymized newborn screening dried bloodspot (DBS) specimens during a 15-month period (October 2020 to December 2021) in Wales (UK) for SARS-CoV-2 IgG-antibodies. We compared newborn DBS antibody-positive rates to the percentage number of pregnant women vaccinated and the percentage number of antibody-positive adults. In December 2021, 47.8% of women in Wales had received two doses of the vaccine by their delivery date; however, only 41.1% of DBS specimens had high antibody concentrations. Results indicate that a proportion of pregnant women remain at higher-risk of COVID complications, particularly given the reduction in antibody neutralization of Omicron versus the Delta variant. Our study demonstrates the utility of newborn screening DBS specimens to monitor SARS-CoV-2 serostatus in pregnant women representing maternal vaccination and natural infection in almost real-time, defining the immunity gap and impact of any interventions.

Performance of Immunoglobulin G Serology on Finger Prick Capillary Dried Blood Spot Samples to Detect a SARS-CoV-2 Antibody Response.

We investigate the diagnostic accuracy and predictive value of finger prick capillary dried blood spot (DBS) samples tested by a quantitative multiplex anti-immunoglobulin G (IgG) assay to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies after infection or vaccination. This cross-sectional study involved participants (n = 6,841) from several serological surveys conducted in nonhospitalized children and adults throughout 2020 and 2021 in British Columbia (BC), Canada. Analysis used paired DBS and serum samples from a subset of participants (n = 642) prior to vaccination to establish signal thresholds and calculate diagnostic accuracy by logistic regression. Discrimination of the logistic regression model was assessed by receiver operator curve (ROC) analysis in an n = 2,000 bootstrap of the paired sample (n = 642). The model was cross-validated in a subset of vaccinated persons (n = 90). Unpaired DBS samples (n = 6,723) were used to evaluate anti-IgG signal distributions. In comparison to paired serum, DBS samples from an unvaccinated population possessed a sensitivity of 79% (95% confidence interval [95% CI]: 58 to 91%) and specificity of 97% (95% CI: 95 to 98%). ROC analysis found that DBS samples accurately classify SARS-CoV-2 seroconversion at an 88% percent rate (area under the curve [AUC] = 88% [95% CI: 80 to 95%]). In coronavirus disease 2019 (COVID-19) vaccine dose one or two recipients, the sensitivity of DBS testing increased to 97% (95% CI: 83 to 99%) and 100% (95% CI: 88 to 100%). Modeling found that DBS testing possesses a high positive predictive value (98% [95% CI: 97 to 98%]) in a population with 75% seroprevalence. We demonstrate that DBS testing should be considered to reliably detect SARS-CoV-2 seropositivity from natural infection or vaccination. IMPORTANCE Dried blood spot samples have comparable diagnostic accuracy to serum collected by venipuncture when tested by an electrochemiluminescent assay for antibodies and should be considered to reliably detect seropositivity following SARS-CoV-2 infection and/or vaccination.

Safety Evaluation of a Medical Congress Held During the COVID-19 Pandemic-A Prospective Cohort.

Objectives: During the COVID-19 pandemic, few scientific congresses have been held on-site. We prospectively evaluated the safety concept of the congress of the Swiss Societies of Infectious Diseases and Hospital Hygiene. Methods: The congress was held in Geneva (Switzerland) while local COVID-19 incidence (with SARS-CoV-2 wild type circulating) was 65/100,000 population (September 2020). A rigorous safety concept was implemented. Congress attendees filled out a questionnaire to assess risk perception, exposures, symptoms and diagnoses of SARS-CoV-2 before, during and after the congress. Dried blood spots were taken on-site and 4 weeks later to detect SARS-CoV-2 seroconversions. Results: Of 365 congress attendees, 196 (54%) either answered the questionnaire (N = 150) or provided baseline and follow-up blood samples (N = 168). None of the participants reported a positive PCR in the 2 weeks after the congress. Five of 168 (3%) participants were seropositive at follow-up, all of which had already been positive at baseline. Conclusion: Findings indicate that congresses with a rigorous safety concept may take place, even in areas with moderately-high COVID-19 activity. Whether this holds true in vaccinated populations and with more transmissible viral variants circulating remains unclear.

Blood neurofilament light in remote settings: Alternative protocols to support sample collection in challenging pre-analytical conditions.

INTRODUCTION: This study investigated alternative pre-analytical handling of blood for neurofilament light (NfL) analysis where resources are limited. METHOD: Plasma NfL was measured with single molecule array after alternative blood processing procedures: dried plasma spots (DPS), dried blood spots (DBS), and delayed 48-hour centrifugation. These were compared to standardized plasma processing (reference standard [RS]). In a discovery cohort (n = 10) and a confirmatory cohort (n = 21), whole blood was obtained from individuals with unknown clinical etiology. In the confirmatory cohort, delayed centrifugation protocol was paired with either 37°C incubation or sample shaking to test the effect of these parameters. RESULTS: Delayed centrifugation (R2 = 0.991) and DPS (discovery cohort, R2 = 0.954; confirmatory cohort, DPS: R2 = 0.961) methods were strongly associated with the RS. Delayed centrifugation with higher temperatures (R2 = 0.995) and shaking (R2 = 0.975) did not affect this association. DPS (P < 0.001) returned concentrations considerably lower than the RS. DISCUSSION: DPS or delayed centrifugation are viable pre-analytical procedures for the accurate quantification of plasma NfL.

Correlation of dried blood spots and plasma for quantification of Immunoglobulin (IgG) against Receptor binding domain and full length spike protein of SARS-CoV-2.

We compared plasma and dried blood spots for detection of SARS-CoV-2 IgG antibodies. There was a good correlation between IgG values measured by both sampling methods, r = 0.935 and 0.965 for Receptor Binding Domain and full-length spike protein of SARS-CoV-2. Bland-Altman assessment showed good agreement between two sampling methods. Dried blood spots is a more pragmatic method for collecting samples for sero-epidemiological surveys of SARS-CoV-2 infection.

mRNA intramuscular vaccination produces a robust IgG antibody response in advanced neuromuscular disease.

SARS-CoV-2 vaccines protect against symptomatic and severe COVID-19. The BNT162b2/Pfizer and mRNA-1273/Moderna vaccines represent new vaccine technology relying on administration of mRNA encoding SARS-CoV-2 viral spike protein encased in lipid nanoparticles. The vaccines are administered as two doses into muscle, which elicits a strong response, typically within 14 days after the second dose. Neuromuscular diseases are characterized by the progressive loss of muscle and are often treated with chronic glucocorticoid steroids, both of which may contribute to a blunted immune response to vaccination. Here, we measured IgG antibody content and neutralizing antibody response after mRNA COVID-19 vaccination in non-ambulatory neuromuscular disease patients. After two doses of mRNA COVID-19 vaccine, median anti-receptor binding domain IgG and percent surrogate viral neutralization in non-ambulatory neuromuscular disease samples were significantly elevated similar to healthy vaccinated controls. As in healthy controls, COVID-19 vaccines produce greater antibody levels compared to those with a history of outpatient COVID-19 infection. This data documents that non-ambulatory neuromuscular disease patients respond well to two doses of mRNA COVID-19 vaccine despite low muscle mass and even chronic steroid use.

Use of Quantitative Dried Blood Spots to Evaluate the Post-Vaccination Level of Neutralizing Antibodies against SARS-CoV-2.

To combat the COVID-19 pandemic, vaccines against SARS-CoV-2 are now given to protect populations worldwide. The level of neutralizing antibodies following the vaccination will evolve with time and vary between individuals. Immunoassays quantifying immunoglobulins against the viral spike (S) protein in serum/plasma have been developed, but the need for venous blood samples could limit the frequency and scale of control in populations. The use of a quantitative dried blood spot (DBS) that can be self-collected would simplify this monitoring. The objective of this study was to determine whether a quantitative DBS device (Capitainer qDBS 10 µL) could be used in combination with an Elecsys anti-SARS-CoV-2 S immunoassay from Roche to follow the development and persistence of anti-S antibodies. This objective was carried out through two clinical studies. The first study investigated 14 volunteers who received two doses of the Comirnaty (Pfizer) vaccine. The levels of anti-S antibodies and the progression over time post-vaccination were studied for three months. The level of produced antibodies varied between subjects, but a similar trend was observed. The anti-S antibodies were highly stimulated by the second dose (×100) and peaked two weeks later. The antibody levels subsequently decreased and three months later were down to 65%. DBS proved to be sufficiently sensitive for use in evaluating the immune status against SARS-CoV-2 over a prolonged time. The second cohort was composed of 200 random patients from a clinical chemistry department in Stockholm. In this cohort, we had no information on previous COVID-19 infections or vaccination. Nevertheless, 87% of the subjects had anti-S immunoglobulins over 0.8 U/mL, and the bias between plasma and DBS proved to be variable, as was also seen in the first vaccination study.

Comparison of Dried Blood Spots and Venous Blood for the Detection of SARS-CoV-2 Antibodies in a Population of Nursing Home Residents.

In the current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, testing for SARS-CoV-2-specific antibodies is paramount for monitoring immune responses in postauthorization vaccination and seroepidemiological studies. However, large-scale and iterative serological testing by venipuncture in older persons can be challenging. Capillary blood sampling using a finger prick and collection on protein saver cards, i.e., dried blood spots (DBSs), has already proven to be a promising alternative. However, elderly persons have reduced cutaneous microvasculature, which may affect DBS-based antibody testing. Therefore, we aimed to evaluate the performance of DBS tests for the detection of SARS-CoV-2 antibodies among nursing homes residents. We collected paired venous blood and DBS samples on two types of protein saver cards (Whatman and EUROIMMUN) from nursing home residents, as well as from staff members as a reference population. Venous blood samples were analyzed for the presence of SARS-CoV-2 IgG antibodies using the Abbott chemiluminescent microparticle immunoassay (CMIA). DBS samples were analyzed by the EUROIMMUN enzyme-linked immunosorbent assay (ELISA) for SARS-CoV-2 IgG antibodies. We performed a statistical assessment to optimize the ELISA cutoff value for the DBS testing using Youden's J index. A total of 273 paired DBS-serum samples were analyzed, of which 129 were positive, as assessed by the reference test. The sensitivities and specificities of DBS testing ranged from 95.0% to 97.1% and from 97.1% to 98.8%, respectively, depending on the population (residents or staff members) and the DBS card type. Therefore, we found that DBS sampling is a valid alternative to venipuncture for the detection of SARS-CoV-2 antibodies among elderly subjects. IMPORTANCE Since the implementation of newly developed SARS-CoV-2 vaccines in the general population, serological tests are of increasing importance. Because DBS samples can be obtained with a finger prick and can be shipped and stored at room temperature, they are optimal for use in large-scale SARS-CoV-2 serosurveillance or postauthorization vaccination studies, even in an elderly study population.

Comparison of IgG and neutralizing antibody responses after one or two doses of COVID-19 mRNA vaccine in previously infected and uninfected individuals.

BACKGROUND: Recent reports have suggested that among individuals previously infected with SARS-CoV-2, a single mRNA vaccine dose is sufficient to elicit high levels of immunity. METHODS: We compared anti-SARS-CoV-2 spike receptor binding domain (RBD) IgG antibody concentrations and antibody-mediated neutralization of spike-angiotensin-converting enzyme (ACE2) receptor binding in vitro following vaccination of non-hospitalized participants by sero-status and acute virus diagnosis history. Participants were analysed before and after mRNA vaccination (BNT162b2/Pfizer or mRNA-1273/Moderna) in a community-based, home-collected, longitudinal serosurvey in the Chicago area (USA); none reported hospitalization for COVID-19. Samples were collected in January and February 2021. Before vaccination, some reported prior positive acute viral diagnostic testing and were seropositive (COVID-19+); the others who did not report acute viral diagnostic testing were categorized as seropositive or seronegative based on anti-spike RBD IgG test results. FINDINGS: Of 307 unique vaccine recipients, 46 reported a prior COVID-19 diagnosis and were seropositive (COVID-19 +). Of the 261 with no history of acute viral diagnostic testing, 117 were seropositive and 144 seronegative before vaccination. The median age was 38 years (range 21-83) with 67 female and 33% male; 40% were non-White. Responses were evaluated after one (n = 142) or two (n = 191) doses of BNT162b2 or mRNA-1273 vaccine. After one dose, median post-vaccine IgG concentration and percent surrogate neutralization were each significantly higher among the COVID-19+ (median 48·2 µg/ml, IgG; > 99.9% neutralization) compared to the seropositives (3·6 µg /ml IgG; 56.5% neutralization) and seronegatives (2·6 µg /ml IgG; 38·3% neutralization). The latter two groups reached > 95% neutralization after the second vaccine dose. INTERPRETATION: After one dose of mRNA vaccine, individuals previously diagnosed with COVID-19 responded with high levels of anti-RBD IgG and surrogate neutralization of spike-ACE2 interaction. One dose of mRNA vaccine was not sufficient to generate comparably high responses among most persons previously infected with SARS-CoV-2 without a clinical COVID-19 diagnosis, nor among seronegative persons. FUNDING: National Science Foundation 2035114, NIH 3UL1TR001422-06S4, and Northwestern University Office of Research.