Serological responses to three doses of SARS-CoV-2 vaccination in inflammatory bowel disease

We read with interest the article by Kennedy et al, which demonstrated adequate serological responses to two-dose regimens of SARS-CoV-2 vaccination in individuals with IBD.1 However, a decay in antibody levels has been shown in the IBD population after two vaccine doses, with anti-tumour necrosis factor (anti-TNF) therapies associated with a more rapid decline.2–4 Despite recommendations for three-dose vaccine regimens for individuals with IBD,5 the uptake has been low in this population.6 We examined the serological response following three doses of mRNA SARS-CoV-2 vaccines in persons with IBD, the factors associated with antibody titres and the decay of antibody titres over time.

Adults aged 18 years or older with a confirmed diagnosis of IBD who received three doses of an mRNA SARS-CoV-2 vaccine (Pfizer-BioNTech BNT162b2 mRNA (Comirnaty) or NIH-Moderna mRNA-1273 (Spikevax)) were recruited from 25 June 2021 to 6 January 2022. Serum samples were drawn at least 1 week following the third dose of vaccine and processed by Alberta Precision Laboratories using the Abbott SARS-CoV-2 IgG II Quant assay to detect antibodies to the S1 subunit of the spike protein (anti-S). The threshold for seroconversion was defined as ≥50 AU/mL for anti-S antibodies. Age, sex, vaccination date and type, IBD type, and IBD medications at time of vaccination were collected through medical chart review. Vaccine schedule between second and third vaccine doses was defined as ‘scheduled’ for 4–18 weeks between dose administration and ‘delayed’ for >18 weeks. Prior history of COVID-19 was defined by either nucleocapsid seroconversion or molecular-confirmed diagnosis of SARS-CoV-2 infection via PCR.7

Lead Researchers

Link to Publication


  1. David Mack

    Senior Scientist, CHEO Research Institute

    View Profile Email