• Jae-Hoon Ko, Eun-Jeong Joo, Su-Jin Park, Jin Yang Baek, Won Duk Kim, Jaehwan Jee, Chul Joong Kim, Chul Jeong, Yae-Jean Kim, Hye Jin Shon, Eun-Suk Kang, Young Ki Choi, and Kyong Ran Peck.
• Division of Infectious Diseases, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 81 Irwon-ro, Gangnam-gu, Seoul 06351, Korea.
• J Clin Med. 2020 Jul 17; 9 (7).

ObjectivesTo investigate antibody production in asymptomatic and mild COVID-19 patients.MethodsSera from asymptomatic to severe COVID-19 patients were collected. Microneutralization (MN), fluorescence immunoassay (FIA), and enzyme-linked immunosorbent assay (ELISA) were performed.ResultsA total of 70 laboratory-confirmed COVID-19 patients were evaluated, including 15 asymptomatic/anosmia, 49 mild symptomatic, and 6 pneumonia patients. The production of the neutralizing antibody was observed in 100% of pneumonia, 93.9% of mild symptomatic, and 80.0% of asymptomatic/anosmia groups. All the patients in the pneumonia group showed high MN titer (≥1:80), while 36.7% of mild symptomatic and 20.0% of asymptomatic/anosmia groups showed high titer (p < 0.001). Anti-SARS-CoV-2 antibodies could be more sensitively detected by FIA IgG (98.8%) and ELISA (97.6%) in overall. For the FIA IgG test, all patients in the pneumonia group exhibited a high COI value (≥15.0), while 89.8% of mild symptomatic and 73.3% of asymptomatic/anosmia groups showed a high value (p = 0.049). For the ELISA test, all patients in the pneumonia group showed a high optical density (OD) ratio (≥3.0), while 65.3% of mild symptomatic and 53.3% of asymptomatic/anosmia groups showed a high ratio (p = 0.006).ConclusionsMost asymptomatic and mild COVID-19 patients produced the neutralizing antibody, although the titers were lower than pneumonia patients. ELISA and FIA sensitively detected anti-SARS-CoV-2 antibodies.

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