• Ryan T Demmer, Brett Baumgartner, Talia D Wiggen, Angela K Ulrich, Ali J Strickland, Brianna M Naumchik, Bruno Bohn, Sara Walsh, Stephen Smith, Susan Kline, Steve D Stovitz, Stephanie Yendell, Timothy J Beebe, and Craig Hedberg.
• Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, Minneapolis; Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY. Electronic address: demm0009@umn.edu.
• Mayo Clin. Proc. 2022 Apr 1; 97 (4): 754760754-760.

AbstractMost SARS-CoV-2 antibody assays cannot distinguish between antibodies that developed after natural infection and those that developed after vaccination. We assessed the accuracy of a nucleocapsid-containing assay in identifying natural infection among vaccinated individuals. A longitudinal cohort composed of health care workers in the Minneapolis/St. Paul area was enrolled. Two rounds of seroprevalence studies separated by 1 month were conducted from November 2020 to January 2021 among 81 participants. Capillary blood from rounds 1 and 2 was tested for IgG antibodies against spike proteins by enzyme-linked immunosorbent assay (spike-only assay). During round 2, IgGs reactive to SARS-CoV-2 nucleocapsid protein (nucleocapsid-containing assay) were assessed. Vaccination status at round 2 was determined by self-report. Area under the curve was computed to determine the discriminatory ability of the nucleocapsid-containing assay for identification of recent infection. Participants had a mean age of 40 years (range, 23 to 66 years); 83% were female. Round 1 seroprevalence was 9.5%. Before round 2 testing, 46% reported vaccination. Among those not recently infected, in comparing vaccinated vs unvaccinated individuals, elevated levels of spike 1 (P<.001) and spike 2 (P=.01) were observed, whereas nucleocapsid levels were not statistically significantly different (P=.90). Among all participants, nucleocapsid response predicted recent infection with an area under the curve of 0.93 (95% CI, 0.88 to 0.99). Among individuals vaccinated more than 10 days before antibody testing, the specificity of the nucleocapsid-containing assay was 92%, whereas the specificity of the spike-only assay was 0%. An IgG assay identifying reactivity to nucleocapsid protein is an accurate predictor of natural infection among a partially vaccinated population, whereas a spike-only assay performed poorly.Copyright © 2022 Mayo Foundation for Medical Education and Research. Published by Elsevier Inc. All rights reserved.

16 keywords...

hide…