Antigenically distinct MF59-adjuvanted vaccine to boost immunity to H5N1

Indications:For prevention of influenza infection in 54 subjects.

Patients:54 subjects; of whom 30 did not previously received H5 Influenza vaccine (unprimed subjects), 12 were primed with nonadjuvanted (plain) H5 Influenza vaccine, and 12 primed with MF59-adjuvanted H5 Influenza vaccine.

TypeofStudy:An open, retrospective study investigating the efficacy of antigenically distinct Influenza vaccine [surface-antigen vaccine against clade 1 A/Vietnam/1194/2004 (NIBRG-14)], adjuvanted with MF-59, in boosting immunity to H5N1 influenza virus in healthy subjects from June through August 2007 in United Kingdom. Letters to the editor.

DosageDuration:2 single doses of 7.5 mcg (low dose), im injection, given 21 days apart.

Results:On each post-vaccination day, mean titers of antibodies to NIBRG-14 and NIBRG-23 were significantly higher among the primed subjects compared to unprimed subjects except on day 42. From day 14 onward, titers of antibodies to both viruses were significantly higher in the MF59-primed group compared to plain-primed group. The highest titers were noted on day 14 in the MF59-primed group, with mean titers of antibodies to NIBRG-14 and NIBRG-23 of 1:378 and 1:347, respectively, on hemagglutination-inhibition assay, and of 1:1754 and 1:2128, respectively, on neutralizing assay. By day 7, at least 80% of MF59-primed subjects had titers of at least 1:40 for all wild type viruses.

AdverseEffects:Influenza vaccine had an acceptable side-effect profiles, and no serious vaccine-related adverse events were observed.

AuthorsConclusions:Our findings indicate that priming subjects with H5 antigen induces a rapidly mobilized, long-lasting immune memory after the administration of low-dose, antigenically distinct vaccine. Given the protective titers detected by day 7, the effect of MF59 adjuvant is striking. Consideration could be given to a proactive vaccine-priming strategy, particularly among those at high risk for pandemic influenza such as health care workers, so that cross-clade antibodies could be rapidly generated after single vaccination or after exposure to the pandemic virus.

FreeText:Tests: hemagglutination-inhibition assay, and neutralizing assay for determination of antibody titers of homologous clade 1 NIBRG-14 and heterologous clade 2.2 NIBRG-23 vaccine reference strains. Concomitant medication: MF-59 adjuvant.