Long-lasting immunogenicity of a virosomal vaccine in older children and young adults with type I diabetes mellitus

Abstract To evaluate the long-lasting immunogenicity and reactogenicity of a virosomal influenza vaccine in subjects with type I diabetes, a trial was conducted during the 2007–2008 influenza season in Milan, Northern Italy. One hundred five subjects aged 9–30 years were randomized to receive by intramuscular injection vaccination by a single dose (0.5 ml) of either a virosomal (Inflexal V® ) ( n = 52) or a standard subunit (Influvac® ) ( n = 53) vaccine. Serum hemagglutinin inhibition antibody titres were determined against the three recommended influenza-like strains, A/H1N1, A/H3N2 and B, at pre-vaccination, and 1 and 6 months post-vaccination. Geometric mean titres were increased in the two groups 1 and 6 months post-vaccination ( P < 0.001). One month post-vaccination both vaccines met the CPMP requirement for immunogenicity with high seroprotection rates (>95%) for strains A/H1N1 and A/H3N2, and a seroprotection of 73% and 70% in the virosomal and subunit vaccine for strain B. Mean fold increase ranged 2.8 (A/H3N2)–6.2 (A/H1N1) in the virosomal group and 2.3 (A/H3N2)–4.8 (A/H1N1) in the subunit group. Immunogenicity declined 6 months post-vaccination in both groups, and the CPMP requirement for immunogenicity was satisfied only in the virosomal group. In subjects without pre-existing antibodies to strain B (titre