key: cord-0876817-zb5i7nb1
authors: Narasimhan, M.; Mahimainathan, L.; Raj, E.; Clark, A. E.; Markantonis, J.; Green, A.; Xu, J.; SoRelle, J. A.; Alexis, C.; Fankhauser, K.; Parikh, H.; Wilkinson, K.; Reczek, A.; Kopplin, N.; Yekkaluri, S.; Balani, J.; Thomas, A.; Singal, A.; Sarode, R.; Muthukumar, A.
title: Clinical evaluation of the Abbott Alinity SARS-CoV-2 spike-specific quantitative IgG and IgM assays in infected, recovered, and vaccinated groups
date: 2021-02-19
journal: nan
DOI: 10.1101/2021.02.17.21251940
sha: 8e17d249469b55b626b4258de9f5a46538cfef34
doc_id: 876817
cord_uid: zb5i7nb1

The COVID-19 pandemic continues to impose a significant burden on global health infrastructure. While identification and containment of new cases remains important, laboratories must now pivot and consider assessment of SARS-CoV-2 immunity in the setting of the recent availability of multiple COVID-19 vaccines. Here we have utilized the latest Abbott Alinity semi-quantitative IgM and quantitative IgG spike protein (SP) serology assays (IgMSP and IgGSP) in combination with Abbott Alinity IgG nucleocapsid (NC) antibody test (IgGNC) to assess antibody responses in a cohort of 1236 unique participants comprised of naive, SARS-CoV-2 infected, and vaccinated (including both naive and recovered) individuals. The IgMSP and IgGSP assays were highly specific (100%) with no cross-reactivity to archived samples recovered prior to the emergence of SARS-CoV-2, including those from individuals with seasonal coronavirus infections. Clinical sensitivity was 96% after 15 days for both IgMSP and IgGSP assays individually. When considered together, the sensitivity was 100%. A combination of NC- and SP-specific serologic assays clearly differentiated naive, SARS-CoV-2-infected, and vaccine-related immune responses. Vaccination resulted in a significant increase in IgGSP and IgMSP titers, with a major rise in IgGSP following the booster (second) dose in the naive group. In contrast, SARS-CoV-2 recovered individuals had several fold higher IgGSP responses than naive following the primary dose, with a comparatively dampened response following the booster. This work illustrates the strong clinical performance of these new serological assays and their utility in evaluating and distinguishing serological responses to infection and vaccination.

Cross-reactivity of the Abbott SARS-CoV-2 IgG SP and IgM SP assays was also evaluated in the setting of respiratory illness and disease conditions, including lupus and hematological malignancies (HM) (primarily multiple myeloma) samples, where antibody production is significantly elevated (Figs. 2C & 2D) . 121 samples obtained prior to SARS-CoV-2 emergence did not cross-react with IgG SP . Interestingly, among 66 HM patient samples collected in 2020, 2 patients (~1.1%) were found to produce a positive value for IgG SP indicating some sort of crossreactivity (Fig. 2C) . One of these cases (a multiple myeloma patient) was confirmed by PCR as having recovered from COVID-19 upon chart review. Interestingly, the second positive patient was repeatedly negative for SARS-CoV-2 by PCR and strongly positive for Hepatitis viral panel serology testing. As no history of SARS-CoV-2 exposure could be established for this patient, further investigation of this IgG SP -specific apparent cross-reactivity is warranted. No crossreactivity was observed in the IgM SP assay (0/187 patients) (Fig. 2D) .

Clinical sensitivity. We evaluated the clinical sensitivity of IgG SP and IgM SP assays in our RT-PCR-positive COVID-19 inpatient cohort where reliable information concerning the date and duration of symptom onset was available. Not surprisingly, we noted that the sensitivity of the assays increased proportionally with time following symptom onset, consistent with the developmental kinetics of a specific antibody response. The sensitivity of IgG SP was 39% and 58% at 5 and 10 days following symptom onset (Table 1 and Fig. s1A ). Extending the analysis of these patients between 16-20 days post symptom onset and beyond revealed a clinical sensitivity of IgG SP assay was 96% and 98% respectively. As expected, clinical sensitivity of IgG SP assay was much higher (74% within 10 days and 100% within 20 days) based on the RT-PCR confirmed date of diagnosis (Table s1 ; Fig. s1B ).

Clinical sensitivity of IgM SP test was comparable to that of the IgG SP test both within 10 days and 20 days post symptom onset. At 20 days symptom onset and beyond, the sensitivity of IgM SP test was 95% (Table 1) , and 82% based on RT-PCR confirmed date of diagnosis All rights reserved. No reuse allowed without permission.

(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted February 19, 2021. ; patients that were both RT-PCR positive and negative for SARS-CoV-2 infection. IgG SP Ab response ranged from 0 to 49517 AU/mL, with a median of 6396 AU/mL (95% CI, 3814 to 9729) ( Fig. 4A) in the vaccinated group. The median antibody level for vaccinated patients was significantly higher (~6400-fold, p<0.0001) relative to those unvaccinated (Fig. 4A) . Intriguingly, ~18% (76/424) of unvaccinated patients had IgG SP titers greater than positive detection threshold despite RT-PCR negativity. IgM SP production was significantly (p<0.0001) higher in the vaccinated versus unvaccinated group, with a more modest median fold increase (~23%, (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted February 19, 2021. ; https://doi.org/10.1101/2021.02.17.21251940 doi: medRxiv preprint following the 1 st dose of vaccination was clearly observed, not surprisingly its distribution was variable (Dark red rectangle; Fig. s3A ). While the number of observations available at or less than 10 days following the 1 st dose was small, 4 of the individuals that were tested had titers under the positive threshold and 2 had titers over 45000 AU/mL. Clearly, after the 2 nd dose of vaccination, the IgG SP titers was consistently high and comparatively exhibited a more uniform trend (Green Oval, Fig. s3A) . Interestingly, 2 patients exhibited a null response following 21 days post vaccination. One of these patients was a HM (multiple myeloma) patient, while the medical history of the other is unknown.

In parallel, SARS-CoV-2-specific IgM SP levels were also increased following vaccination in the naïve subjects ( Fig. 4B & s3B) . In particular, the distribution analysis demonstrated that following the primary dose of vaccination at week 1 and week 2, ~71% of the subjects had values above the positive threshold (Fig. s3B) . However, at 21 days and beyond post booster dose, IgM SP levels again rose, and a noticeable over-the threshold cluster was seen compared to the primary vaccination (Fig. s3B) . Although the number of Moderna-vaccinated recipients in this evaluation is modest, both the IgG SP and IgM SP responses appeared to be comparable to that of individuals who received the Pfizer-BioNTech formulation.

Vaccination response in naïve population. Next, we compared the IgG SP response after the first and booster dose in the naïve vaccinated group that was derived by filtering out for IgG NC (15, 16) . These data raise (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (recovered) group after primary and booster vaccine dose.

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(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted February 19, 2021. ;

Threshold of different antibody assays used to predict the different conditions when used in combination in our dataset (filtered in) All rights reserved. No reuse allowed without permission.

(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted February 19, 2021. ; https://doi.org/10.1101/2021.02.17.21251940 doi: medRxiv preprint

Table s1). Importantly, when IgG SP and IgM SP results were combined and analyzed for assay

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Single dose vaccination in healthcare workers previously infected with SARS-CoV-2. MedRxiv

No reuse allowed without permission. (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity