Serological response to the 2009 H1N1 influenza vaccination in patients with inflammatory bowel disease

Influenza vaccination is recommended for patients with inflammatory bowel disease (IBD). The 2009 H1N1 influenza vaccine produced seroprotection rates of >85% in the general population but there are no data on the immunogenicity of the vaccine in patients with IBD.

An observational prospective open-label study was conducted to examine the immunogenicity of the 2009 H1N1 influenza vaccine in 108 patients with IBD. Patient details, medications and disease activity were recorded. Pre- and post-vaccination haemagglutinin inhibition titres and geometric mean titres were measured. A functional assay of T lymphocyte activity was measured at vaccination in a subset of patients as an alternative measure of immunosuppression. Subjects were followed for 6 months post-vaccination.

Of 108 patients enrolled, 105 completed the study. The post-vaccination seroprotection rate was 50%. Immunosuppressed subjects had a lower rate of seroprotection than non-immunosuppressed subjects (44% vs 64%, p=0.06). The proportion with seroprotection was significantly lower in subjects on combination immunosuppression than in those receiving no immunosuppression (36% vs 64%, p=0.02). Patients receiving combined immunosuppression had a significantly lower fold increase in geometric mean titres than those on monotherapy immunosuppression (3.5 vs 11.5, p=0.03). An assay of T lymphocyte activity was performed in a subgroup of 48 subjects. Those with intermediate activity had lower seroprotection than those with high activity (28% vs 61%, p=0.02). The vaccine was well tolerated.

Patients with IBD vaccinated with the 2009 H1N1 influenza vaccine had a low rate of seroprotection, particularly among those who were immunosuppressed. Although there is a need for studies of the clinical benefit of vaccines in this population, patients with IBD need to be aware of this reduced immunogenicity.