key: cord-1038822-rhbbdmxf authors: Zeng, Fanfan; Wu, Mengjun; Wang, Jinbiao; Li, Jianyu; Hu, Guoyun; Wang, Lin title: Over 1‐year duration and age difference of SARS‐CoV‐2 antibodies in convalescent COVID‐19 patients date: 2021-07-26 journal: J Med Virol DOI: 10.1002/jmv.27152 sha: d5f7780f73e7b1a0266a27f67f1d0e5233a02a5b doc_id: 1038822 cord_uid: rhbbdmxf Anti‐severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) immunoglouilin G (IgG) and immunoglouilin M (IgM) antibodies have been widely used to assist clinical diagnosis. Our previous study reported a discrepancy in SARS‐CoV‐2 antibody response between male and female coronavirus disease 2019 (COVID‐19) patients. However, the duration and discrepancy between ages as well as sexes of SARS‐CoV‐2 antibody in convalescent COVID‐19 patients have not been clarified. In this study, a total of 538 health‐examination individuals who were confirmed with SARS‐CoV‐2 infection a year ago were enrolled. Blood samples were collected and detected for IgM and IgG antibodies. Among these convalescent patients, 12.80% were detected positive for IgM antibodies. The positive rates for IgM antibody were close between sexes: for males, this is 9.17% and for females 13.75%. However, the IgG antibody was detected positive in as much as 82.90% convalescent patients and the positive rates were nearly the same between males (82.57%) and females (82.98%). Besides this, the level of IgM and IgG antibodies showed no difference between male and female convalescent patients. The level of IgG antibodies showed a significant difference between ages. The elder patients (over 35 years old) maintained a higher level of IgG antibody than the younger patients (under or equal 35 years old) after recovering for 1 year. In addition, IgG antibody was more vulnerable to disappear in younger patients than in elder patients. Overall, our study identified over 1‐year duration of SARS‐CoV‐2 antibody and age difference of IgG antibody response in convalescent COVID‐19 patients. These findings may provide new insights into long‐term humoral immune response, vaccines efficacy and age‐based personalized vaccination strategies. The coronavirus disease 2019 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still ongoing and has caused substantial morbidity and mortality. 1 As of May 31, 2021, more than 171,000,000 confirmed cases and 3,500,000 deaths had been reported worldwide. To control the spread of SARS-CoV-2 infection, serum rapid detection of SARS-CoV-2 specific immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies have been widely applied in the clinic to assist diagnosis of infection. [2] [3] [4] Owing to its high sensitivity, serum SARS-CoV-2 antibody detection plays important roles in the identification and isolation of COVID-19 patients. 5 The levels of IgM and IgG antibodies against SARS-CoV-2 nucleoprotein and surface spike protein receptor-binding domain increase gradually after infection. 6 The IgM antibody is detectable as early as 5 days after symptom onset and the IgG antibody is detectable in one week after symptom onset. 7 It was reported that the IgM antibody level peaked in 2 weeks and then began to decline and disappear, whereas the IgG antibody level continued to go up, reached its peak in 3 weeks, and maintained at a high level beyond 7 weeks. 3, 8 However, whether the IgM and IgG could persist for a longer time is unclear. Our previous study identified a discrepancy in the SARS-CoV-2 IgG antibody response between male and female COVID-19 patients, 8 while little is known about the SARS-CoV-2 antibodies response in convalescent patients between different sexes as well as ages. In this study, a total of 538 convalescent COVID-19 patients who came to the Union Hospital for a 1-year annal health examination were enrolled. Blood samples were collected from all these individuals and detected for SARS-CoV-2 specific IgM and IgG antibody. By analyzing SARS-CoV-2 antibodies, we identified that 12.80% convalescent patients remained IgM antibody positive and as much as 82.90% convalescent patients still persisted as IgG antibody positive after 1 year of recovery, and no significant difference were observed in antibodies positive rates and average levels between male and female convalescent patients. Noteworthily, we found that the IgG antibody level in younger convalescent patients was significantly lower than elder convalescent patients and the negative rate of IgG antibody in younger patients was higher than elder patients after 1 year of recovery. These findings of our study may be helpful to understand the long-term duration of humoral immune response, herd immunity and the efficacy of vaccines, which are major concerns in controlling the COVID-19 pandemic. A total of 538 COVID-19 convalescent patients were enrolled in this study. All the patients were once confirmed as COVID- 19 This SARS-CoV-2 antibody detecting system has been widely used in clinics and medical research. [9] [10] [11] [12] Briefly, serum and SARS-CoV-2 antigencoated magnetic particles were incubated for 20 min. After washing, the mouse anti-human IgM or IgG antibody labeled with acridinium was added and incubated for 4 min. Following another washing cycle, pretrigger, and trigger solutions were added to the reaction mixture. The In this study, GraphPad 6.0 (GraphPad Software Inc.) was applied for mapping and data statistical analysis. The positive rates of IgM and IgG antibodies were analyzed by χ 2 test. The levels of IgM and IgG antibodies were presented as mean ± SEM and analyzed by using one-way snalysis of variance followed by Dunnett's test or Mann-Whitney U test as indicated in the figure legends. A p value of less than 0.05 was considered statistically significant. The result showed that in all the eight groups, no significant difference was observed for IgM antibody levels, and so too for IgG antibody levels ( Figure 1C,D) . The above analysis indicated that there was no difference in IgM and IgG antibody levels between male and female convalescent COVID-19 patients who have recovered for 1 year. 3.3 | The SARS-CoV-2 IgG antibody presented a lower level and a higher negative rate in the younger convalescent patients than the elder convalescent patients Next, male and female patients were grouped together to analyze the antibody dynamics going with age. The results showed that the average level of SARS-CoV-2 IgM antibody was stable, with slight fluctuations around 5 AU/ml, and no significant differences were observed between any of the age groups ( Figure 2A) . However, the levels of SARS-CoV-2 IgG antibody showed significant differences in patients of different ages. The average level of IgG antibody was relatively low, about 50 AU/ml, in the younger (21-35 years old) convalescent patients and gradually increased to about 80 AU/ml in the elder patients ( Figure 2B) . Notably, the average levels of IgG antibody for the three younger groups (21-25, 26-30, and 31-35) were all less than 60 AU/ml, while for the elder groups (36-40, 41-45, 46-50, 51-55, and 56-66), the average levels of IgG antibody were all more than 60 AU/ml ( Figure 2B ). All convalescent patients were then divided into two groups based on the levels of the SARS-CoV-2 IgG antibody. Further analysis showed that the average level of SARS-CoV-2 IgG antibody in patients under or equal 35 years old was significantly lower than that of patients over 35 years old ( Figure 2C ). In addition, among patients under or equal 35 years old, the percentage of SARS-CoV-2 IgG negative was much higher than that of patients over 35 years old, although no statistical difference was observed ( Figure 2D ). This data indicated that the SARS-CoV-2 IgG antibody in elder convalescent patients was more stable and persisted at a higher level than the younger convalescent patients after recovery for 1 year. Monitoring the humoral immune response and its duration after SARS-CoV-2 infection is essential for the assessment of reinfection risk and evaluation of vaccine efficacy. However, the duration of The humoral immune response after vaccination and specific vaccination strategy for people in different age groups needs further clinical investigation. A previous study showed that SARS-CoV-2 IgM peaked in the 2nd week after the onset of symptoms, and then decreased until disappeared in the 16th week after the onset of symptoms. 24 In this study, we reported that the SARS-CoV-2 IgM persisted positive in 12. Technology. The authors declare no conflict of interest. The data that support the findings of this study are available from the author Fanfan Zeng, upon reasonable request. 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