Seasonal influenza epidemics are associated with high morbidity and mortality particularly in high-risk patients. Conventionally administered influenza vaccines show reduced efficacy in populations with weakened immune systems such as solid-organ transplant patients. This study assesses the safety and immunogenicity of an intradermally administered influenza vaccine in renal transplant patients previously identified as non-responders to a licensed trivalent inactivated influenza vaccine (TIV). Renal transplant patients with low or no hemagglutination inhibiting (HI) antibody response to an A influenza (H3N2) vaccine strain were enrolled in a descriptive phase II, open-label, randomized, multicentre trial: 31 received an investigational intradermal TIV, and 31 received a conventionally administered TIV. Both vaccines contained 15 μg hemagglutinin (HA) per strain. The 62 study subjects were selected from 201 renal transplant patients aged 18-60 years who had been vaccinated in the previous year with a conventionally administered TIV. Vaccination was safe and well tolerated by each administration route. The immunogenicity results of this descriptive study showed ID TIV vaccination to induce HI antibody responses that trended higher in renal transplant patients than conventionally administered TIV. Our results suggest that ID influenza vaccination may offer enhanced immunogenicity and protection in persons who do not respond well to conventional TIV. Further studies should be conducted in immunocompromised populations to validate the trends for higher efficacy of ID vs. conventional route of immunization against influenza.
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