Evaluation of Ortho VITROS and Roche Elecsys S and NC Immunoassays for SARS-CoV-2 Serosurveillance Applications

Comparison of SARS-CoV-2 seroprevalence estimates between commercial lab serum specimens and blood donor specimens, United States, September-December 2021

We estimated monthly cross-sectional seroprevalence rates of anti-nucleocapsid (anti-N) and anti-spike (anti-S) antibodies to severe acute respiratory syndrome coronavirus 2 in two U.S. nationwide studies. The nationwide blood donor seroprevalence (NBDS) study included specimens from blood donors, while the nationwide commercial laboratory seroprevalence (NCLS) study included residual serum specimens tested in commercial laboratories for reasons unrelated to the assessment of coronavirus disease 2019 infection. In September-December 2021, specimens collected from both nationwide studies were tested for anti-N antibodies. In September-October 2021, specimens from both studies within a five-state area were tested for anti-S antibodies. We used raking methods to adjust all seroprevalence estimates by the population distribution of key demographics in included states. Seroprevalence estimates of each antibody type were compared across the two studies for specimens drawn in the same U.S. states during the same time period. Our analysis revealed that over a 4-month period, national NCLS monthly anti-N estimates were 0.5-1.9 percentage points higher than NBDS estimates. In contrast, across five states during a 2-month period, NBDS anti-S estimates were 7.6 and 8.2 percentage points higher than NCLS estimates. The observed differences in seroprevalence estimates between the NBDS and NCLS studies may be attributed to variations in the characteristics of the study sample populations, particularly with respect to health status, health behaviors, and vaccination status. These differences should be considered in the interpretation of seroprevalence study results based on blood donors or commercial lab residual specimens.

IMPORTANCE

This study was the first systematic comparison between two nationwide severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) studies which estimated seroprevalence, or the proportion of the population with antibodies to the virus, using differing convenience sample populations. One study tested blood donor specimens; the other study tested specimens left over from clinical blood tests. The seroprevalence of anti-nucleocapsid and anti-spike antibodies was compared in the same states during the same months with statistical adjustments based on state demographics. Similar anti-nucleocapsid antibody seroprevalence estimates produced by two independent studies using differing convenience samples build confidence in the generalizability of their anti-nucleocapsid findings. Due to high blood donor vaccine rates, blood donor SARS-CoV-2 anti-spike antibody estimates might overestimate general population seroprevalence, an important consideration for interpreting national seroprevalence study results. Furthermore, because laboratory residuals and blood donations are two common sources of specimens for seroprevalence studies, study findings may be informative for other respiratory virus seroepidemiology studies.

Detection of Nucleocapsid Antibodies Associated with Primary SARS-CoV-2 Infection in Unvaccinated and Vaccinated Blood Donors

Nucleocapsid antibody assays can be used to estimate SARS-CoV-2 infection prevalence in regions implementing spike-based COVID-19 vaccines. However, poor sensitivity of nucleocapsid antibody assays in detecting infection after vaccination has been reported. We derived a lower cutoff for identifying previous infections in a large blood donor cohort (N = 142,599) by using the Ortho VITROS Anti-SARS-CoV-2 Total-N Antibody assay, improving sensitivity while maintaining specificity >98%. We validated sensitivity in samples donated after self-reported swab-confirmed infections diagnoses. Sensitivity for first infections in unvaccinated donors was 98.1% (95% CI 98.0-98.2) and for infection after vaccination was 95.6% (95% CI 95.6-95.7) based on the standard cutoff. Regression analysis showed sensitivity was reduced in the Delta compared with Omicron period, in older donors, in asymptomatic infections, <30 days after infection, and for infection after vaccination. The standard Ortho N antibody threshold demonstrated good sensitivity, which was modestly improved with the revised cutoff.

SARS-CoV-2 immunoassays in a predominantly vaccinated population: Performances and qualitative agreements obtained with two analytical approaches and four immunoassays

BACKGROUND AND OBJECTIVES

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serosurveys are typically analysed by applying a fixed threshold for seropositivity ('conventional approach'). However, this approach underestimates the seroprevalence of anti-nucleocapsid (N) in vaccinated individuals-who often exhibit a difficult-to-detect anti-N response. This limitation is compounded by delays between the onset of infection and sample collection. To address this issue, we compared the performance of four immunoassays using a new analytical approach ('ratio-based approach'), which determines seropositivity based on an increase in anti-N levels.

MATERIALS AND METHODS

Two groups of plasma donors and four immunoassays (Elecsys total anti-N, VITROS total anti-N, Architect anti-N Immunoglobulin G (IgG) and in-house total anti-N) were evaluated. First-group donors (N = 145) had one positive SARS-CoV-2 polymerase chain reaction (PCR) test result and had made two plasma donations, including one before and one after the PCR test (median = 27 days post-PCR). Second-group donors (N = 100) had made two plasma donations early in the Omicron wave.

RESULTS

Among first-group donors (97.9% vaccinated), sensitivity estimates ranged from 60.0% to 89.0% with the conventional approach, compared with 94.5% to 98.6% with the ratio-based approach. Among second-group donors, Fleiss's κ ranged from 0.56 to 0.83 with the conventional approach, compared with 0.90 to 1.00 with the ratio-based approach.

CONCLUSION

With the conventional approach, the sensitivity of four immunoassays-measured in a predominantly vaccinated population based on samples collected ~1 month after a positive test result-fell below regulatory agencies requirement of ≥95%. The ratio-based approach significantly improved the sensitivities and qualitative agreement among immunoassays, to the point where all would meet this requirement.

Nucleocapsid and Spike Protein-Based Anti-SARS-CoV-2 Assay Performance in the Minority and Rural Coronavirus Insights Study: Characteristics of Socioeconomically Disadvantaged Populations with Health Disparities

BACKGROUND

COVID-19 has had a devastating impact on Black, Hispanic, and other underserved, disadvantaged populations. Here anti-SARS-CoV-2 tests are characterized in disadvantaged patients to examine equivalence in US populations.

METHODS

Underserved participant adults (age > 18 years) were enrolled before the availability of SARS-CoV-2 vaccines in Federal Qualified Health Centers in California, Florida, Louisiana, Illinois, and Ohio and contributed samples to the Minority and Rural Coronavirus Insights Study (MRCIS). A subset coined the MRCIS SARS-CoV-2 Antibody Cohort of 2365 participants was tested with the Roche Anti-SARS-CoV-2 assay (Cobas e601). Five hundred ninety-five of these were also tested with the Ortho Clinical Diagnostics VITROS Anti-SARS-CoV-2 IgG assay (VITROS-5600); 1770 were also tested with the Abbott ARCHITECT SARS-CoV-2 IgG assay (ARCHITECT-2000). Assay-specific cutoffs classified negative/positive results.

RESULTS

Eight point four percent (199/2365) of the MRCIS SARS-CoV-2 Antibody Cohort was SARS-CoV-2 RNA positive at enrollment. Agreement between the Ortho/Roche and the Abbott/Roche antibody testing did not vary by enrollment RNA status. The Ortho (anti-spike protein) vs Roche (anti-nucleocapsid protein) comparison agreed substantially: kappa = 0.63 (95% CI: 0.57-0.69); overall agreement, 83%. However, agreement was even better for the Abbott vs Roche assays (both anti-nucleocapsid protein tests): kappa = 0.85 (95% CI: 0.81-0.87); overall agreement, 95%. Anti-SARS-CoV-2 comparisons stratified by demographic criteria demonstrated no significant variability in agreement by sex, race/ethnicity, or age.

CONCLUSIONS

Analytical agreement is 96.4% for anti-spike-protein vs anti-nucleocapsid-protein comparisons. Physiologically, seroreversion of anti-nucleocapsid reactivity after infection occurred in the disadvantaged population similarly to general populations. No anti-SARS-CoV-2 assays included demonstrated a clinically significant difference due to the demographics of the disadvantaged MRCIS SARS-CoV-2 Antibody Cohort.

Long-Term Symptoms Associated With SARS-CoV-2 Infection Among Blood Donors

Importance

Long-term symptoms, lasting more than 4 consecutive weeks after acute COVID-19 disease, are an important consequence of SARS-CoV-2 infection. Many prior studies have lacked a non-SARS-CoV-2-infected control population to distinguish background prevalence of symptoms from the direct impact of COVID-19 disease.

Objective

To examine the prevalence of long-term physical and mental health symptoms associated with SARS-CoV-2 infection in a large population of blood donors based on self-report and serologic test results.

Design, Setting, and Participants

This cross-sectional study included American Red Cross blood donors (aged ≥18 years) who were surveyed between February 22 and April 21, 2022, about new long-term symptoms arising after March 2020 and their SARS-CoV-2 infection status. All participants underwent at least 1 serologic test for antinucleocapsid antibodies between June 15, 2020, and December 31, 2021.

Exposures

SARS-CoV-2 infection as defined by a self-reported, confirmed acute infection or antinucleocapsid antibody positivity.

Main Outcomes and Measures

New long-term symptoms since March 2020, including 5 symptom categories (neurologic, gastrointestinal, respiratory and cardiac, mental health, and other).

Results

Among 818 361 individuals who received the survey, 272 965 (33.4%) responded, with 238 828 meeting the inclusion criteria (138 576 [58.0%] female; median [IQR] age, 59.0 [47.0-67.0] years). Of the 83 015 individuals with a history of SARS-CoV-2 infection, 43.3% reported new long-term symptoms compared with 22.1% of those without a history of SARS-CoV-2 infection. After controlling for age, sex, race and ethnicity, and number of underlying conditions, those with a history of SARS-CoV-2 infection had an increased odds of new long-term symptoms compared with those without (adjusted odds ratio [AOR], 2.55; 95% CI, 2.51-2.61). Female sex and a history of chronic conditions were associated with new long-term symptoms. Long-term symptoms in the other category (AOR, 4.14; 95% CI, 4.03-4.25), which included changes in taste or smell, and the respiratory and cardiac symptom categories (AOR, 3.21; 95% CI, 3.12-3.31) were most associated with prior SARS-CoV-2 infection. Mental health long-term symptoms were also associated with prior SARS-CoV-2 infection (AOR, 1.05; 95%, CI, 1.02-1.08).

Conclusions and Relevance

This study's findings suggest that long-term symptoms lasting more than 4 weeks are common in the adult population, but there is a significantly higher prevalence among those with SARS-CoV-2 infection. Continued efforts to define and track long-term sequelae of SARS-CoV-2 using a control group without infection and serologic information to include those who had asymptomatic or unidentified infections are needed.

Prevalence of SARS-CoV-2 infection among US blood donors by industry, May-December 2021

BACKGROUND

Work is a social determinant of health that is often overlooked. There are major work-related differences in the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and death, but there have been few analyses of infection rates across industry groups. To date, only one national assessment of SARS-CoV-2 infection prevalence by industry based on self-report has been completed. No study has looked at seroprevalence of COVID-19 by industry.

METHODS

During May-December 2021, blood donors with SARS-CoV-2 antinucleocapsid testing were sent an electronic survey about their work. Free-text industry responses were classified using the North American Industry Classification System. We estimated seroprevalence and 95% confidence intervals (CIs) of SARS-CoV-2 infection by industry.

RESULTS

Of 57,726 donors, 7040 (12%, 95% CI: 11.9%-12.5%) had prior SARS-CoV-2 infection. Seroprevalence was highest among Accommodation & Food Services (19.3%, 95% CI: 17.1%-21.6%), Mining, Quarrying, and Oil and Gas Extraction (19.2%, 95% CI: 12.8%-27.8%), Healthcare & Social Assistance (15.6%, 95% CI: 14.9%-16.4%), and Construction (14.7%, 95% CI: 13.1%-16.3%). Seroprevalence was lowest among Management of Companies & Enterprises (6.5%, 95% CI: 3.5%-11.5%), Professional Scientific & Technical Services (8.4%, 95% CI: 7.7%-9.0%), and Information (9.9%, 95% CI: 8.5%-11.5%).

CONCLUSIONS

While workers in all industries had serologic evidence of SARS-CoV-2 infection, certain sectors were disproportionately impacted. Disease surveillance systems should routinely collect work characteristics so public health and industry leaders can address health disparities using sector-specific policies.

Evaluation of Ortho VITROS and Roche Elecsys S and NC Immunoassays for SARS-CoV-2 Serosurveillance Applications

SARS-CoV-2 seroprevalence studies are instrumental in monitoring epidemic activity and require well-characterized, high-throughput assays, and appropriate testing algorithms. The U.S. Nationwide Blood Donor Seroprevalence Study performed monthly cross-sectional serological testing from July 2020 to December 2021, implementing evolving testing algorithms in response to changes in pandemic activity. With high vaccine uptake, anti-Spike (S) reactivity rates reached >80% by May 2021, and the study pivoted from reflex Roche anti-nucleocapsid (NC) testing of Ortho S-reactive specimens to parallel Ortho S/NC testing. We evaluated the performance of the Ortho NC assay as a replacement for the Roche NC assay and compared performance of parallel S/NC testing on both platforms. Qualitative and quantitative agreement of Ortho NC with Roche NC assays was evaluated on preselected S/NC concordant and discordant specimens. All 190 Ortho S+/Roche NC+ specimens were reactive on the Ortho NC assay; 34% of 367 Ortho S+/Roche NC- specimens collected prior to vaccine availability and 43% of 37 Ortho S-/Roche NC+ specimens were reactive on the Ortho NC assay. Performance of parallel S/NC testing using Ortho and Roche platforms was evaluated on 200 specimens collected in 2019 and 3,903 study specimens collected in 2021. All 200 pre-COVID-19 specimens tested negative on the four assays. Cross-platform agreement between Roche and Ortho platforms was 96.4% (3,769/3,903); most discordant results had reactivity close to the cutoffs on the alternate assays. These findings, and higher efficiency and throughput, support the use of parallel S/NC testing on either Roche or Ortho platforms for large serosurveillance studies. IMPORTANCE Seroprevalence studies like the U.S. Nationwide Blood Donor Seroprevalence Study (NBDS) have been critical in monitoring SARS-CoV-2 epidemic activity. These studies rely on serological assays to detect antibodies indicating prior infection. It is critical that the assays and testing algorithms used in seroprevalence studies have adequate performance (high sensitivity, high specificity, ability to discriminate vaccine-induced and infection-induced antibodies, etc.), as well as appropriate characteristics to support large-scale studies, such as high throughput and low cost. In this study we evaluated the performance of Ortho's anti-nucleocapsid assay as a replacement for the Roche anti-nucleocapsid assay and compared performance of parallel anti-spike and anti-nucleocapsid testing on both platforms. These data demonstrate similar performance of the Ortho and Roche anti-nucleocapsid assays and that parallel anti-spike and anti-nucleocapsid testing on either platform could be used for serosurveillance applications.