Serological assays for differentiating natural COVID-19 infection from vaccine induced immunity

Authors:

• Cheng, Samuel M.S.
• Lau, Jonathan J.
• Tsang, Leo C.H.
• Leung, Kathy
• Lee, Cheuk Kwong
• Hachim, Asmaa
• Kavian, Niloufar
• Chaothai, Sara
• Wong, Ricky W.K.
• Yu, Jennifer K.M.
• Chai, Zacary Y.H.
• Mori, Masashi
• Wu, Chao
• Yiu, Karen
• Hui, David S.C.
• Amarasinghe, Gaya K.
• Poon, Leo L.M.
• Wu, Joseph T.
• Valkenburg, Sophie A.
• Peiris, Malik

Details:

Journal of Clinical Virology, Volume 170, 2024-02-29

Article Link: Click here

Background Natural SARS-CoV-2 infection may elicit antibodies to a range of viral proteins including non-structural protein ORF8. RNA, adenovirus vectored and sub-unit vaccines expressing SARS-CoV-2 spike would be only expected to elicit S-antibodies and antibodies to distinct domains of nucleocapsid (N) protein may reliably differentiate infection from vaccine-elicited antibody. However, inactivated whole virus vaccines may potentially elicit antibody to wider range of viral proteins, including N protein. We hypothesized that antibody to ORF8 protein will discriminate natural infection from vaccination irrespective of vaccine type. Methods We optimized and validated the anti-ORF8 and anti-N C-terminal domain (NCTD) ELISA assays using sera from pre-pandemic, RT-PCR confirmed natural infection sera and BNT162b2 (BNT) or CoronaVac vaccinees. We then applied these optimized assays to a cohort of blood donor sera collected in April-July 2022 with known vaccination and self-reported infection status. Results We optimized cut-off values for the anti-ORF8 and anti-N-CTD IgG ELISA assays using receiver-operating-characteristic (ROC) curves. The sensitivity of the anti-ORF8 and anti-N-CTD ELISA for detecting past infection was 83.2% and 99.3%, respectively. Specificity of anti-ORF8 ELISA was 96.8 % vs. the pre-pandemic cohort or 93% considering the pre-pandemic and vaccine cohorts together. The anti-N-CTD ELISA specificity of 98.9% in the pre-pandemic cohort, 93% in BNT vaccinated and only 4 % in CoronaVac vaccinated cohorts. Anti-N-CTD antibody was longer-lived than anti-ORF8 antibody after natural infection. Conclusions Anti-N-CTD antibody assays provide good discrimination between natural infection and vaccination in BNT162b2 vaccinated individuals. Anti-ORF8 antibody can help discriminate infection from vaccination in either type of vaccine and help estimate infection attack rates (IAR) in communities.