Background: Little is known about the serologic response to natural influenza infection in transplant recipients. We describe the hemagglutinin antibody response to influenza A/H1N1 infection in this population.

Methods: We prospectively enrolled solid organ transplant (SOT) and hematopoietic stem cell transplant (HSCT) patients with acute influenza infection in a multicenter study. Serum samples were taken at diagnosis and four weeks later. Hemagglutination inhibition assays (HIA) were measured against year-specific vaccine strains. Seroconversion and seroprotection were defined as a 4-fold titer increase and HIA titers of ≥40, respectively.

Results: Paired sera were available at diagnosis and 4 weeks for 229 patients (177 influenza A, 51 influenza B, 1 untyped). A majority had influenza vaccine in the same season (141/209 (67.5%)). Seroprotection rates at diagnosis for seasonal vaccine strains were 17.5% (40/229) for H1N1, 64.2% (147/229) for H3N2 and 66.3% (152/229) for influenza B. We further analyzed 78 patients infected with H1N1 strain (63 SOT, 15 HSCT). The median time from transplant to infection was 3.0 (IQR 0.5-7.6) years. All patients were treated with oseltamivir. Seroprotection rates at diagnosis were similar in those who were previously vaccinated in the same influenza season (19.4% vs. 8.6%, p=0.37). Only 34.6% patients achieved seroconversion 4 weeks after infection. Patients who had received vaccine in the same influenza season were less likely to seroconvert (OR 0.3 95%CI 0.1-0.9, p=0.02). Pneumonia at diagnosis was present in 22/78 (28.2%). Patients with pneumonia at diagnosis were more likely to seroconvert (OR 4.3 95%CI 1.4-14.1, p<0.01). In addition, H1N1 seroprotection rates were higher 4 weeks after infection in patients with pneumonia than those without (15/22(68.2%) vs. 22/56 (39.3%); p=0.02). Early antiviral treatment within 48 hours of symptoms did not affect seroconversion rates (p=0.61).

Conclusion: This study provides unique data on humoral immune response during and after seasonal influenza infection in transplant patients. Many patients still develop influenza despite protective antibody. Patients with more severe disease have increased strain-specific antibody responses suggesting that failure to seroconvert does not reflect the inability to control infection.

CITATION INFORMATION: Hirzel C., Ferreira V., L'Huillier A., Hoschler K., Cordero E., Reid G., Englund J., Limaye A., Humar A., Kumar D. Humoral Immune Response to Seasonal Influenza Infection in Transplant Recipients Am J Transplant. 2017;17 (suppl 3).

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