Background and aims: Our first objective was to evaluate the immune response to the adjuvanted 2009 A/H1N1 pandemic (pH1N1) vaccine in inflammatory bowel disease (IBD) patients treated with anti-TNF-α alone or combined with immunosuppressants (IS). Second and third aims were the safety of pH1N1 vaccine and the effects on IBD clinical activity.

Methods: 36 patients with Crohn's disease (CD) and 26 with ulcerative colitis (UC) and thirty-one healthy control (HC) subjects were enrolled. 47 patients were on anti TNF-α maintenance monotherapy and 15 on anti TNF-α combined with IS. Sera were collected at baseline (T0) and 4 weeks after the vaccination (T1) for antibody determination by hemagglutination inhibition (HAI). Disease activity was monitored at T0 and T1.

Results: Seroprotective titers (≥ 1:40) in patients were comparable to HC. Seroconvertion rate (≥ 4 fold increase in HAI titer) was lower than HC in IBD patients (p = 0.009), either on anti TNF-α monotherapy (p = 0.034) or combined with IS (p = 0.011). Geometric mean titer (GMT) of antibodies at T1 was significantly lower in patients on combined therapy versus those on monotherapy (p = 0.0017) and versus HC (p = 0.011). The factor increase of GMT at T1 versus T0 was significantly lower in IBD patients versus HC (p = 0.042), and in those on combined immunosuppression, both versus monotherapy (p = 0.0048) and HC (p = 0.0015). None of the patients experienced a disease flare.

Conclusion: Our study has shown a suboptimal response to pH1N1 vaccine in IBD patients on therapy with anti TNF-α and IS compared to those on anti-TNF-α monotherapy and HC.