Antibody Responses to SARS CoV 2 in Coronavirus Diseases 2019 Patients with Different Severity

Background More understanding of antibody responses in the SARS-CoV-2 infected population is useful for vaccine development. Aim To investigate SARS-CoV-2 IgA and IgG among COVID-19 Thai patients with different severity. Methods We used plasma from 118 adult patients who have confirmed SARS-CoV-2 infection and 49 patients under investigation without infection, 20 patients with other respiratory infections, and 102 healthy controls. Anti-SARS-CoV-2 IgA and IgG were performed by enzyme-linked immunosorbent assay from Euroimmun. The optical density ratio cut off for positive test was 1.1 for IgA and 0.8 for IgG. The association of antibody response with the severity of diseases and the day of symptoms was performed. Results From Mar 10 to May 31, 2020, 289 participants were enrolled, and 384 samples were analyzed. Patients were categorized by clinical manifestations to mild (n = 59), moderate (n = 27) and severe (n = 32). The overall sensitivity of IgA and IgG from samples collected after day 7 is 87.9% (95% CI 79.8-93.6) and 84.8% (95% CI 76.2-91.3), respectively. The severe group had a significantly higher level of specific IgA and IgG to S1 antigen compared to the mild group. All moderate to severe patients have specific IgG while 20% of the mild group did not have any IgG detected after two weeks. Interestingly, SARS-CoV-2 IgG level was significantly higher in males compared to females among the severe group (p = 0.003). Conclusion The serologic test for SARS-CoV-2 has high sensitivity after the second week after onset of illness. Serological response differs among patients with different severity and different sex. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by funding to support Biobank from Ratchadapisek Sompoch Fund, Faculty of Medicine, Chulalongkorn University. We would like to thank the health care team for at King Chulalongkorn Memorial hospital, Thai Red Cross, particularly Dr. Kampol Suwanpimolkul, Dr. Leilanee Paitoonpong, and Dr. Suvaporn Anulgulreungkitt. Special thanks for the advice from Dr. Parvapan Bhattarakosol and statistical analysis by Miss Jiratchaya Sophonphan. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was reviewed and approved by the Institutional Review Board of Faculty of Medicine (IRB number 242/63) and National Blood Center, Thai Red Cross Society (COA No. NBC 5/2020). All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All the data was presented in the manuscript.