Immunogenicity of a monovalent, aluminum-adjuvanted influenza whole virus vaccine for pandemic use

In the case of an influenza pandemic a significant gap between influenza vaccine manufacturing capacities and vaccine demands must be expected on a global scale. This study explores the possibility to increase the number of vaccine doses that can be provided with the existing resources by using a lower amount of antigen per dose in an aluminum-adjuvanted whole virus vaccine formulation, instead of the standard dosage of 15 microg hemagglutinin (HA). The study was performed as an open, non-controlled, randomized, multicentric study in 200 volunteers (18-30 years of age). Three monovalent aluminum-adjuvanted whole virus formulations with different antigen concentrations (1.9, 3.75 and 7.5 microg HA per dose) were compared to a split virus vaccine (15 microg HA per dose) without aluminum adjuvantation. The sera were tested for hemagglutination inhibition (HI) antibodies, neuraminidase inhibition (NI) antibodies and virus neutralizing (VN) antibodies. Nasal swab samples were tested for influenza-specific IgA antibodies. All volunteers were immunologically na?ve to the vaccine strain influenza A/Singapore/1/57 (H2N2). The vaccine was well tolerated. HI titers reached protective levels (geometric mean titer (GMT) >1:40) after two vaccine doses. In the group immunized with the lowest antigen dose the seroprotection rate was 82%. Although the immune response tends to be lower for vaccine formulations with reduced antigen content, the immunogenicity criteria as defined by the European Agency for the Evaluation of Medicinal Products (EMEA) were met with all antigen formulations after two vaccine doses. Significant increases in HI, NI and VN titers were observed, however, no significant local immune response was detected. The use of a low-dose whole virus influenza vaccine, adjuvanted with aluminum appears to be a viable approach to increase vaccine supplies in a pandemic situation.