key: cord-0926700-54oj7ttc
authors: Yan, Xiquan; Chen, Guoqiang; Jin, Zhaoxia; Zhang, Zhongwei; Zhang, Bing; He, Jiangming; Yin, Siqing; Huang, Juanshu; Fan, Maiying; Li, Zhenyuan; Chen, Fang; Zeng, Yong; Han, Xiaotong; Zhu, Yimin
title: Anti‐SARS‐CoV‐2 IgG levels in relation to disease severity of COVID‐19
date: 2021-08-21
journal: J Med Virol
DOI: 10.1002/jmv.27274
sha: e03577a8b239193fae63f1f93ab99e33f4e95e2f
doc_id: 926700
cord_uid: 54oj7ttc

The durability of infection‐induced severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) immunity has crucial implications for reinfection and vaccine effectiveness. However, the relationship between coronavirus disease 2019 (COVID‐19) severity and long‐term anti‐SARS‐CoV‐2 immunoglobulin G (IgG) antibody level is poorly understood. Here, we measured the longevity of SARS‐CoV‐2‐specific IgG antibodies in survivors who had recovered from COVID‐19 1 year previously. In a cohort of 473 survivors with varying disease severity (asymptomatic, mild, moderate, or severe), we observed a positive correlation between virus‐specific IgG antibody titers and COVID‐19 severity. In particular, the highest virus‐specific IgG antibody titers were observed in patients with severe COVID‐19. By contrast, 74.4% of recovered asymptomatic carriers had negative anti‐SARS‐CoV‐2 IgG test results, while many others had very low virus‐specific IgG antibody titers. Our results demonstrate that SARS‐CoV‐2‐specific IgG persistence and titer depend on COVID‐19 severity.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can cause various outcomes that range from asymptomatic infection to serious pneumonia, acute respiratory distress syndrome, or multiple organ dysfunction, and even death. [1] [2] [3] [4] [5] [6] [7] The strength of infectioninduced SARS-CoV-2 immunity has crucial implications for reinfection and vaccine effectiveness. However, the relationship between coronavirus disease 2019 (COVID-19) severity and long-term immunoglobulin G (IgG) antibody level is poorly understood. Here, we measured the longevity of SARS-CoV-2-specific IgG antibodies in survivors who had recovered from COVID-19 1 year previously. Baseline demographic and laboratory examination results were extracted from electronic medical records.

According to the clinical manifestations, COVID-19 was classified as asymptomatic, mild, moderate, or severe (further details can be found in our previous work). 4 Serum IgG antibodies against recombinant SARS-CoV-2 nucleoprotein (N) and spike protein (S) were detected using a chemiluminescence method (AutoLumo A2000Plus; Autobio) according to the manufacturer's instructions. An antibody level of ≥1 signal to cutoff ratio (S/CO) was considered positive and a level of <1 S/CO was considered negative. Statistical analyses and preparation of figures were carried out using SPSS (SPSS Inc.) or Origin (OriginLab).

The study was approved by the Hunan Provincial People's Hospital Ethics Commission. All individuals provided written or verbal consent to participate.

A total of 473 COVID-19 survivors participated in this study.

Descriptive data for the study population are presented in Table 1 

In this observational study, we evaluated SARS-CoV-2-specific IgG in 473 survivors who had recovered from COVID-19 1 year previously.

Titers of SARS-CoV-2-specific IgG varied substantially and were not detectable in 78 survivors.

We found that 74.4% of recovered asymptomatic carriers were negative for SARS-CoV-2-specific IgG, while those with positive test results had very low virus-specific IgG titers. By contrast, survivors who recovered from severe COVID-19 had relatively higher anti-SARS-CoV-2 IgG titers. Similar findings have been documented for other viral infectious diseases (e.g., SARS, middle east respiratory syndrome) whose etiologies involve a significant contribution of immunopathogenesis. 8, 9 The mechanism underlying the relationship between anti-SARS-CoV-2 IgG titers and COVID-19 severity remains unclear. Severe COVID-19, caused by excessive inflammation and/or uncontrolled SARS-COV-2 replication, may lead to overproduction of antibodies.

Associations between COVID-19 severity and SARS-CoV-2 viral load in plasma, nasopharyngeal, and sputum specimens were identified in a previous study. 10 

The authors declare that there are no conflict of interests.

Comparison of the level of IgG against SARS-CoV-2 between asymptomatic, mild, moderate, and severe patients. The boxplots show medians (middle line) and third and first quartiles (boxes), while the whiskers show 1.5× the interquartile range (IQR) above and below the box. Numbers of patients (n) are shown underneath. The results were expressed as mean {log2 (Fluorescence intensity)} ± SD in different groups. Analysis of variance (ANOVA) was conducted to test the difference in means among groups. IgG, immunoglobulin G

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