key: cord-0939935-932vzeg2
authors: Luo, Chunhua; Liu, Min; Li, Qianyuan; Zheng, Xiaoling; Ai, Wen; Gong, Feng; Fan, Jinhong; Liu, Shaowei; Wang, Xi; Luo, Jun
title: Dynamic changes and prevalence of SARS-CoV-2 IgG/IgM antibodies: multiple factors-based analysis
date: 2021-04-28
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2021.04.078
sha: fbcfb85fa44305f193a2bb10428538a253413129
doc_id: 939935
cord_uid: 932vzeg2

Objective Investigating the dynamic characteristics of serologic antibodies against SARS-CoV-2 is of significance. Method Here, the dynamic changes and prevalence of IgM and IgG antibodies against SARS-CoV-2 from symptoms onset to 210 days were described. Antibodies were detected by a chemiluminescence immunoassay. Result For all patients, the average titers and positive rates of IgG/IgM within 30 days from symptoms onset reached to the peak and then began continuous decline. The titers and positive rates of IgG/IgM from symptoms 180 to 210 days remained 43.1 ± 27.0 AU/mL/84.3% and 4.4 ± 5.2 AU/mL/12.0%, respectively. Further statistical analysis revealed that the dynamic changes and prevalence in the SARS‐CoV‐2 IgG/IgM antibodies are mainly based on age and disease severity, not sex. The change trend of dynamic and prevalence of IgM antibody was similar as the description of IgG. Even so, the decline rate of IgM antibody is faster. The IgG level that reduced to 16.33 ± 3.15 AU/mL might be a threshold value and should be alerted because the IgG level might become undetectable within 30 to 60 days when the IgG down to the threshold value. Conclusion These results could provide important information for COVID-19 diagnosis, treatment, and vaccine development.

The pandemic caused by SARS-CoV-2 coronavirus still led to significant morbidity and mortality worldwide. Although Nucleic acid detection has been regarded as the gold standard of COVID-19 laboratory diagnosis, serologic test is valuable in developing rapid clinical diagnosis, vaccines and treatment of COVID-19 (Shen et al., 2020) .

Neutralizing antibodies (NAbs) produced by immune response, play vital roles against the SARS-CoV-2. IgG/IgM antibodies are specific SARS-CoV-2 antibodies and could detected rapidly within two weeks from symptom onset (Pérez-García et al., 2020) . IgM antibody is the key indicators of on-going or current infection, which develops earliest after exposure to the pathogen. IgG antibody named as protective antibody, a symbol of recovery of the disease or past infection, is the most common antibodies of the immunological response and could protect the host from infection by blocking viral entry into host cells after viral infection. Factors affecting the development of IgG/IgM antibodies are extensive. Some studies propose that virusspecific IgG antibodies decrease rapidly by approximately 3 months after infection Wang et al., 2021) , and others papers indicate that IgG antibodies have stable titers detected over several weeks or several months (Dan et al., J o u r n a l P r e -p r o o f 2021). Many studies noticed that the age, sex and disease severity had effect on the dynamic characteristics of serologic antibodies (Kong W-h et al., 2020; O'Driscoll et al., 2020; , however, the research population selected is not comprehensive or the time of antibody observation is not long enough. This paper represents a retrospective analysis of dynamic changes and prevalence of SARS-CoV-2 IgG/IgM antibodies based on multiple factors, from symptoms onset to 210 days.

This retrospective study was conducted at Yichang Central people's Hospital. All patients were clinically diagnosed with laboratory-confirmed COVID-19 and discharged based on the National recommendations for diagnosis and treatment of pneumonia caused by 2019-nCoV. The criteria for the initial diagnosis and discharge of patients have been described in the our ago paper in detail . In brief, epidemiology survey, imaging features, laboratory examinations and clinical characteristics are mainly reference. The positive nucleic acid testing result is the ultimately confirmed reference. Otherwise, some information should be added. Novel coronavirus asymptomatic infection: symptoms and signs lack no related clinical manifestations, such as fever, cough, sore throat and other symptoms, which could be perceived or recognized clinically, but the nucleic acid testing result is positive based on the detection in respiratory tract or other specimens. These asymptomatic patients were found in screening of populations that have close contact with confirmed J o u r n a l P r e -p r o o f patients or in community screening. Mildly symptomatic infection: the clinical symptoms were mild and there was no clinical manifestation of pneumonia. The antibodies of patients are tested periodically based on the requirement from the municipal prevention and control headquarters. Medical records were also reviewed for detail demographic and clinical information. The study was approved by the Ethics Committees from Yichang Central people's Hospital. The patients in the study signed informed consent forms or agreed by the phone. IgG/IgM antibodies of above patients were tested in different time interval from disease onset. The date of the antibody testing is calculated as follows: the time from symptoms onset to the testing time under 30 days would be defined as from symptoms onset to 30 days, the time from symptoms onset to the testing time between 30 to 60 days would be defined as from symptoms 30 to 60 days, the time from symptoms onset to the testing time between 60 to 90 days would be defined as from symptoms 60 to 90 days, and so on.

Serum IgG/IgM antibodies were detected using a chemiluminescence immunoassay (Shenzhen Yafilong Biological Technology Co., Ltd, IgG/IgM kits) in an iFlash 3000-A as described in the paper previously . The cut-off value of IgM and IgG recommended by the manufacturer is 10 AU/mL. The recombinant antigens contain nucleoprotein and spike protein of SARS-CoV-2. All operations in the detection were based on the manufacturer's protocols.

Statistical analyses in this study were performed with Prism 6.0 (GraphPad, San J o u r n a l P r e -p r o o f Diego, USA). Categorical variables were compared using Chi square test. The

Mann-Whitney U test was employed for comparing SARS-CoV-2 IgG/IgM antibodies titers. A P value less than .05 was accepted statistically significant.

As shown in J o u r n a l P r e -p r o o f 56.56 ± 14.37 and 62.19 ± 10.11 years old. In critical group, the average age of whole COVID-19, male and female patients were 68.54 ± 9.50, 64.64 ± 9.92 and 72.43 ± 9.07 years old. The average hospitalization time (Table 1) for the whole patients were 26.10 ± 6.30 days. The average hospitalization time for four group patients including mildly symptomatic, general, severe and critical were 20.55 ± 7.58 days, 22.36 ± 6.35 days, 29.00 ± 6.33 days, 32.47 ± 4.65 days, respectively. It should be noted that for symptomatic patients, hospitalization time was unavailable because these patients were isolated in designated places instead of hospitalization.

To elucidate whether the dynamic and positive rate change of the SARS-CoV-2 IgG/IgM were related to the sex, we analyzed the titers and calculate the positive rate of the IgG/IgM in male and female patients from disease onset to 210 days. As shown in Fig.1 A and 1B , the titers of IgG/IgM rose to a peak, which the average antibody titer (Table 2) were 167.2 ± 49.3 AU/mL and 169.9 ± 47.8 AU/mL for IgG, 123.0±145.8 AU/mL and 103.3±118.9AU/mL for of IgM, respectively, in female and male patients with 30 days post symptom onset. Then the average titers of IgG decreased continuously. As shown in Table 2 , the average titers of IgG in female and male patients from disease 30 days to 60 days downed to the 62.8% and 50.3% of the peak value and remained in relatively stable levels from symptoms 150 to 210 days, about 23.1% to 29.7% of the peak. The dynamic change of the SARS-CoV-2 IgG/IgM in female and male had no significant difference, shown in Fig.1A and 

As shown in Fig.2A and 2B , the titers of IgG/IgM rose to a peak with 30 days post symptom onset in four age groups. The average antibody titer of IgG was 250.6 ± 6.9 AU/mL, 158.4 ± 60.9 AU/mL, 187.3± 32.7 AU/mL and 157.9 ± 50 AU/mL within 30 days post symptom onset in different age groups. Then the average titers of IgG decreased continuously. The average titers of IgG decreased faster in younger age group and the titer of IgG remained relatively stable level, ranging from 6.7% to 11%, 16.5% to 26.8%, 19.9% to 27.7% and 25.8 % to 31.2%, of the peak, shown in Table 2, from 150 days to 210 days post symptom onset in four different age groups. The whole dynamic trend in different age groups had no significant difference (P >0.05).

The ultimately average antibody titers of IgG were higher in old ages. As shown in Fig.2C , the positive rate of IgG in different age patients peaked up to 100%/91.7%/100%/98.1% within 30 days, then declined slowly to remain at 91.8%/83.4% in elder age groups, however, quickly to remain at 60%/78.6% in younger age groups. There is a significant difference in the positive rate among different age groups (P= 0.04). To IgM, the titer level ( Fig. 1B and Table 2 ) peaked within 30 days post symptom onset. Then the titer declined quickly and became J o u r n a l P r e -p r o o f undetectable after disease onset 90 days except for the age group ranging from 45 to 65. The positive rate of IgM is higher in elder age groups, as shown in Fig.2C .

To investigate the association of antibody dynamic change to the severity of the disease, we plotted the average antibody level from asymptomatic, mild, general, severe and critical groups at different intervals. As shown in Fig.3A and 3B, the titers of IgG/IgM in different disease severity groups are different. As described above, the titers of IgG/IgM rose to a peak with 30 days post symptom onset for groups. Then the average titers of IgG decreased continuously. On the whole, the IgG level change is based the disease severity. In critical group, the decrease rate of IgG is the lowest and the titer is the highest. As a contrast, in asymptomatic group, the decrease rate of IgG is the fastest. Meanwhile, the positive rate of IgG is the highest in severe group and critical group. To IgM, the titer level ( Fig. 1B and Table 4 ) peaked within 30 days post symptom onset. Then the titer declined quickly and became undetectable after disease onset 90 days except for severe and critical groups. The positive rate of IgM is higher in both severe and critical groups, as shown in Fig.3C .

15 patients, whose antibody testing results were positive and turned negative in the next detection at 30 to 60 days interval attracted our eyes. In order to determine the level of IgG antibody that IgG antibody might become undetectable in patients within a period of time because of degradation when IgG antibody downed to the J o u r n a l P r e -p r o o f level, we made a statistical analysis of the two consecutive IgG antibody results of these patients. As shown in Fig.4, for 15 patients, the average level of previous IgG antibody before negative results is 16.33 ± 3.15 AU/mL. Therefore, 16.33 ± 3.15 AU/mL might be a key IgG level, which indicates the IgG level might become undetectable within 30 to 60 days because of subsequent degradation. We defined the level as a threshold of IgG antibody that should be alerted.

More comprehensive understanding of the characteristics of SARS-CoV-2 IgM and IgG antibodies, including its dynamics over time, its determinants, would offer implications for the diagnosis and treatment of COVID-19.

Retrospective data in this study revealed that female population was more likely to be infected by SARS-CoV-2 than male, which is consistent with our ago report . Although, no significant differences were found in sex, involved to compare the dynamic changes and prevalence of SARS-CoV-2 IgG/IgM antibodies.

The decline positive rate of IgM antibody is lower and the average titer of IgM antibody is relatively higher in female from disease onset to 60 days, which might be the reason of higher level of SARS-CoV-2 IgG antibody observed in female patient in disease early phase in other papers Tian et al., 2020) .

As the same with the previous study reported, elderly people in this study were more susceptible to be infected (Yang et al., 2020) . Further, we found that the SARS-CoV-2 IgM and IgG antibodies titers significantly increased along with age, which support the view that elderly patients might have stronger immune response against J o u r n a l P r e -p r o o f SARS-CoV-2 than young patients.

Besides, we also demonstrated that the titers and positive rates SARS-CoV-2 IgM / IgG antibodies are related to the disease severity. The titers and positive rates SARS-CoV-2 IgM / IgG antibodies in severe group and critical group were higher than in asymptomatic or mild cases, which matches with other previous studies (Garcia-Beltran et al., 2021; Chen et al., 2020) . The titers and positive rates SARS-CoV-2 IgM / IgG antibodies in asymptomatic group decreases faster. The positive rate of IgG antibodies in severe group and critical group had almost no decline from disease onset to 210 days.

In this study, we observed that the persistence of IgG could keep at least seven months. As shown in Fig.4 , the IgG level that reduced to 16.33 ± 3.15 AU/mL should be alerted because the IgG level might become undetectable within 30 to 60 days, which might contribute to offering the reference value in monitoring effective vaccine-related antibody level. Otherwise, there were 1 patient who did not develop either positive IgG or IgM antibody from disease onset to 210 days. Findings in this study raise concern that immunity response against SARS-CoV-2 may failed in persons. The positive rate of IgM antibody in population had 12% at disease 210 days, especially slightly higher in severe and critical groups. Whether the existence of IgM antibody indicate the potential risk of virus needs to be studied. At least, our current observations and data do not support that this existence of IgM antibody will lead to COVID-19 outbreak again.

Some shortcomings in this study are inevitable. First of all, continuously monitor J o u r n a l P r e -p r o o f the changes of antibody titer in the same patient from symptom onset to 210 days would increase the persuasion of conclusion. Otherwise, the scale in some groups is small.

In summary, our study identified that the dynamic changes and prevalence in the SARS-CoV-2 IgG/IgM antibodies dynamics are mainly affected by age and disease severity, not sex, and predicted a threshold value of IgG level in patients that should be alerted because the IgG level might become undetectable within 30 to 60 days when the IgG down to the threshold value. These results could provide important information for COVID-19 diagnosis, treatment, and vaccine development in future.

The study was approved by the Ethics Committees from Yichang Central people's Hospital.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 92:2050-2054. Note: As stands for asymptomatic, M stands for mildly symptomatic, C stands for general, S stands for severe and Cr stands for critical. 

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The work was financially supported by the National Natural Science Foundation of