Antibody persistence 1 year after pandemic H1N1 2009 influenza vaccination and immunogenicity of subsequent seasonal influenza vaccine among adult organ transplant patients

We investigated the antibody persistence in solid organ transplant (SOT) recipients 1year after immunization with two doses of monovalent AS03-adjuvanted influenza A(H1N1)pdm09 vaccine. We also assessed the boosting effect of the seasonal trivalent inactivated vaccine 2010 (TIV/10) that contained the influenza A(H1N1)pdm09 strain. A total of 49 SOT recipients and 11 healthy controls were included. After a blood sample was obtained to assess the persistent immunity, one dose of TIV/10 was administered and another blood sample was collected 1month after vaccination. A(H1N1)pdm09 antibodies were measured using a haemagglutination inhibition assay. The percentage of SOT recipients with protective titres decreased between 1month and 10-14months after the monovalent influenza A(H1N1)pdm09 vaccination, from 79% (n=38) to 47% (n=23) (P=0.02). The corresponding numbers for the control group were 100% and 63%, respectively (P=0.008). After the TIV/10 boosting dose, the number of SOT recipients with protective titres increased from 47% (n=23) to 71% (n=35) (P=0.2). All the controls reached a protective titre level. The median titre rise was significantly higher among controls when compared to SOT recipients (P=0.0036). No rejection or adverse events were seen. The results show an obvious need for vaccine boosting doses in the SOT patients. (ClinicalTrials.gov number: NCT01256931).