Background/Purpose: An adjuvanted pandemic H1N1 influenza (pH1N1) vaccine (Pandemrix®) was reported as highly immunogenic resulting in seroconversion in 77-94% of adults after administration of a single dose. The aim of the present study was to investigate impact of different anti-rheumatic treatments on antibody response to pH1N1 vaccination in patients with rheumatoid arthritis (RA) and spondylarthropathy (SpA).

Methods: Patients with arthritis (n=291; mean age 57 years, 64% women) participated. Hemagglutination inhibition (HI) assay was performed on blood samples drawn before and after a mean (SD) of 8.3 (4) months following vaccination. A positive immune response i.e. seroconverstion was defined as negative prevaccination serum and postvaccination HI titer ≥40 or a ≥4-fold increase in HI titer. There were 7 treatment groups: 1) RA on methotrexate (MTX); 2) RA on anti-TNF monotherapy; 3) RA on anti-TNF+MTX; 4) RA on other biologics (abatacept, rituximab, tocilizumab); 5) SpA on anti-TNF monotherapy; 6) SpA on anti-TNF+MTX and 7) SpA on NSAIDs/analgesics. Predictors of positive immune response were studied using logistic regression analysis.

Results: The percentage of patients with positive immune response in the different treatment groups were: 1) 42% 2) 53% 3) 43% 4) 20% 10%, 50%  5) 76% 6) 47% and 7) 59%, respectively. RA patients on rituximab had significantly lower (p<0.001) and SpA on anti-TNF monotherapy significantly better response rates compared to other treatment groups (p 0.001-0.033). Higher age (p<0.001) and current smoking predicted impaired immune response (p=0.025). Antibody titers  3-6 months after vaccination were generally lower compared to those within first 3 months but no further decrease in titers were observed  6-22 months after vaccination.

Conclusion: Rituximab treatment severely reduced antibody response to pH1N1 influenza vaccine. All other treatments groups showed lower although acceptable antibody response. Serological immunity seems to be stable for 22 months in the current patient population, with the exception of rituximab (and possibly abatacept) treated patients.