Verona et al. to 14 CO-index (IQR: 3.4C37.6) and declined further to 9.8 CO-index at 12?months (IQR: 2.8C9.8). When classified by age groups, the only statistically significant difference in anti-N-IgG between the two age groups (30?years and Rabbit Polyclonal to FZD2 >30?years) was identified at 12?month time point (median difference 8.06, = 0.035). Spearman correlation coefficient was negatively Epimedin A1 associated between anti-N-IgG and time interval (= ?0.255, = 0.000) but was not statistically significant with age of a patient (> 0.05). Conclusions: In conclusion, SARS-CoV-2 antibody levels started declining after 6?months but remained detectable in the majority of patients up to 12?months. Keywords: SARS-CoV-2, COVID-19, serology, IgG, antibody, nucleocapsid Introduction Severe acute respiratory syndrome-corona virus-2 (SARS-CoV-2) reportedly surfaced in the Chinese city of Wuhan in late 2019.1,2 The virus spread rapidly throughout the globe, and in just couple of months, the total reported cases of infection crossed 20?million. The World Health Organization (WHO) declared it a pandemic on 11 March 2020. Until 11 January 2022, more than 308?million individuals were reportedly infected with SARS-CoV-2 infection. Additionally, 5.4?million SARS-CoV-2-associated deaths were reported across the globe. 3 Reverse transcriptase-polymerase chain reaction (RT-PCR) is currently used as the gold standard for acute COVID-19 diagnosis. 4 In the first 7?days after the onset of contamination, the sensitivity for detection of virus in RT-PCR is 66.7% which decreases afterward. 5 Alternatively, serological assessments which are based on the humoral responses of the human body become positive after 1C3?weeks of the contamination.5,6 Antibodies are produced against different epitopes of SARS-CoV-2 including receptor-binding domain name (RBD), spike glycoprotein, and nucleocapsid protein. 7 Among these, the nucleocapsid is usually more immunogenic, highly expressed, and more sensitive to detection than spike protein.7,8 Nucleocapsid antigen plays an important role in viral pathogenesis, it has numerous epitomes that stimulate T and B cell responses, and is suitable for vaccine formulation. 9 It has been reported that COVID-19 patients become seronegative gradually with some studies suggesting rapid decline within few months post-COVID-19 contamination.10,11 Epimedin A1 However, there is limited research available regarding the post-infection persistence and response to SARS-CoV-2 virus up to 12?months period. This study collected periodic samples (quarterly) from 120 HCWs previously infected with SARS-CoV-2 contamination up to 12?months from their enrolment into the study to understand the magnitude and sturdiness of the anti-nucleocapsid IgG antibodies titer in the long run. Material and methods Participant cohort This was a single-arm follow-up study. Healthcare workers who participated in this study were employees of Prime Foundation (PF) group of teaching hospitals, Peshawar city, Pakistan. Healthcare workers including doctors, nurses, and paramedical staff were invited to participate. A total number of 134 HCWs previously infected with COVID-19 contamination (confirmed by RT-PCR) were included in the study while severely ill Epimedin A1 participants were excluded. Nine HCWs decreased out after first follow-up and five after second follow-up (Physique 1: flow chart). All participants provided written informed consent for study participation. The study was approved by Institutional Review Board (IRB) of Prime Foundation. Blood samples were collected periodically (quarterly) from the study cohort between July, 2020 and April 2021 at four time points (July 2020, Oct 2020, Jan 2021, and April 2021). Open in a separate window Physique 1. Flow chart. Blood sampling and serological testing SARS-CoV-2 recombinant (N) protein (IgG) Five milliliter of blood sample was collected and kept in lithium heparin bottles. Samples were centrifuged and serum was isolated. SARS-CoV-2 antibodies in the serum sample were identified using the Roche assay (Roche, Basel, Switzerland): an electro-chemiluminescence immunoassay that uses a protein expressing the nucleocapsid antigen (N) binding (sensitivity of 100% and specificity of 99.8%). The producers instructions were followed for the full total effect.