Material and Methods:
Study design and population:
This was a prospective longitudinal cohort study involving 36 health care workers (HCW) and 19 cirrhosis patients at King George’s Medical University and Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow. Blood samples of 10 healthy unvaccinated (and unexposed as per history) individuals were obtained from rural area and they were referred for vaccination at primary health care center. The normal healthy HCW were defined as without any co-morbidity or medication. Patients were selected for the cirrhotic group based on clinical, biochemical and radiological finding along as well as evidence of portal hypertension and AST-Platelet ratio index. Hepatic decompensation was determined by the presence of ascites or hepatic encephalopathy in cases of hepatitis B-related liver cirrhosis, or by a markedly raised serum bilirubin level along with prolonged prothrombin time or international normalized ratio >1.5. 20 Venous blood was collected from all participants before receiving the first dose (day 0) and before booster dose (day 270±14 after second dose or ≅ one year after first dose). The time interval between first and second dose was three months as per government protocol at the time of vaccination. Samples were collected in plain and EDTA vial for anti-SARS-CoV-2 antibody and flow cytometry assay respectively. All participant signed written informed consent form and study was approved by institutional ethical committee.
Serological assay:
Anti-receptor binding domain (RBD) or anti-Spike antibody titer and neutralizing antibody (NAb) were measured in stored serum sample by double-antigen sandwich enzyme-linked immunoassay (ELISA) through Elecsys® Anti-SARS-CoV-2 S (Roche Diagnostics GmbH, Germany) and SARS-CoV-2 Neutralizing Antibody competitive ELISA Kit (Invitrogen, Thermo-Fischer) respectively. The Elecsys® Anti-SARS-CoV-2 S antibody titer is expressed as U/mL and value >0.8 U/mL was considered positive (quantitation limit of 0.40–250 U/mL). For SARS-CoV-2 Neutralizing Antibody, samples with more than 20% calculated neutralization were considered positive.