Vaccination against coronavirus disease-19 (COVID-19) is effective in preventing the occurrence or reduction in the severity of the infection. Patients with inflammatory bowel disease (IBD) are on immunomodulators, which may alter serological response to vaccination against COVID-19. Accordingly, we studied (i) the serological response to vaccination against COVID-19 in IBD patients and (ii) a comparison of serological response in IBD patients with that in healthy controls. A prospective study was undertaken during a 6-month period (July 2021 to January 2022). Seroconversion was assessed among vaccinated, unvaccinated IBD patients and vaccinated healthy controls using anti-severe acute respiratory syndrome coronavirus 2 immunoglobulin G (anti-SARS-CoV-2 IgG) antibody detection enzyme-linked immunosorbent assay (ELISA) kit, and optical density (OD) was measured at 450 nm. OD is directly proportional to the antibody concentration. One hundred and thirty-two blood samples were collected from 97 IBD patients (85 [87.6%] ulcerative colitis and 12 [12.4%] Crohn's disease). Forty-one of the seventy-one (57.7%) unvaccinated and 60/61 (98.4%) vaccinated IBD patients tested positive (OD 0.3) for SARS-CoV-2 IgG antibodies. Fourteen of the sixteen (87.5%) healthy controls tested positive for SARS-CoV-2 IgG antibodies. Vaccinated IBD patients had higher ODs than unvaccinated IBD patients (1.31 [1.09-1.70] vs. 0.53 [0.19-1.32], p 0.001) and 16 vaccinated healthy controls (1.31 [1.09-1.70] vs. 0.64 [0.43-0.78], p 0.001). Three of the seventy-one (4.2%) unvaccinated IBD patients reported having recovered from COVID-19. Most IBD patients seroconvert after vaccination against SARS-CoV-2, similar to a healthy population. A large proportion of IBD patients had anti-SARS-CoV-2 antibodies even before vaccination, suggesting the occurrence of herd immunity.
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