Durable immune response to inactivated H1N1 vaccine is less likely in children with sickle cell anemia receiving chronic transfusions.

BACKGROUND: Defects in the immune system may affect vaccine responsiveness. Because of the splenic hypofunction and abnormal opsonic activity, it was unknown whether patients with sickle cell disease (SCD) would respond appropriately to H1N1 vaccination. The objective of this study was to assess seroprotective post-vaccine H1N1 antibody response in children with SCD. PROCEDURE: Serum antibody titers were measured by hemagglutination inhibition and microneutralization (MN) assays. Correlations were established between clinical and treatment parameters and immune response.
RESULTS: Twenty-nine of 38 (76.3%) subjects (mean age 11 ± 5.4 years) had durable protective antibody titers 8 ± 1.6 months (range 5-12 months) post-vaccination. Lessened immune response was not associated with time interval from vaccination, splenectomy, or hydroxyurea treatment. Lack of antibody response was associated with age less than 3 years and treatment with chronic transfusions. Of the nine non-responders, seven were on chronic transfusions (39% unresponsiveness rate in the transfused group). The difference in the number of patients with seropositivity between the non-transfused and the transfused groups was statistically significant (P = 0.039).
CONCLUSIONS: Most subjects were able to mount an influenza-specific antibody response against the inactivated H1N1 vaccine. Similar to the general population, children less than 3 years were less likely to respond. In addition, patients on chronic transfusions were less likely to respond when compared to non-transfused children. Clinicians should be aware of the possibility of decreased vaccine response in patients with SCD on chronic transfusions. We postulate that transfusion-related immunomodulation (TRIM) may be related to decreased response.