Immunization with Low Dose Adjuvanted Split H5N1A/Indonesia/5/2005 Vaccine Protects Ferrets against Challenge with Wild-Type Heterosubtypic H5N1 A/Hong Kong/156/1997 Virus
Session VI – Mallett, Corey, Poster Only
Title of Contribution: Immunization with Low Dose Adjuvanted Split H5N1A/Indonesia/5/2005 Vaccine Protects Ferrets against Challenge with Wild-Type Heterosubtypic H5N1 A/Hong Kong/156/1997 Virus
Author(s): C. Mallett1, B. Baras2, S. Mossman2, K. Stittelaar3, J. Simon3, A. Osterhaus3,4, D. Burt1, and R. Kenney5
Affiliation(s): GlaxoSmithKline Biologicals, Canada1; Belgium2; and US5; ViroClinics, Netherlands3; Erasmus Medical College, Netherlands4
Abstract: Background and Aim: Adjuvantation is considered a key antigen-sparing strategy for pre-pandemic and pandemic influenza vaccines. This preclinical study was undertaken to evaluate the immunogenicity and efficacy of low doses of an H5N1 vaccine composed of monovalent detergent-split antigen formulated with AS03 Adjuvant System in a stringent ferret H5N1 heterologous challenge model.
Study Design: Ferrets (8 per group) seronegative for influenza virus by anti-nucleoprotein ELISA were immunized intramuscularly on days 0 and 21 with 3.75 mcg (based on HA) of detergent-split A/Indonesia/5/2005 antigen formulated with AS03 or 3.75, 1.5, 0.6, or 0.24 mcg of the same antigen formulated with half the volume of AS03. The control group received 3.75 mcg of A/Indonesia split antigen alone. All animals were bled on days 0, 21, 42, and 48 to determine the pre-challenge serum antibody titers to the vaccine strain. On day 49, all animals were challenged intratracheally with one hundred thousand TCID50 of wild-type A/Hong Kong/156/1997 virus. All animals were monitored for morbidity, mortality, and viral shedding in the pharynx during a 5-day post-challenge observation period. On day 54, all surviving animals were euthanized and the viral load in lung tissue was determined.
Results: At all antigen doses formulated with AS03 or half the volume of AS03 adjuvant, the HI and neutralization titers to the vaccine strain (H5N1 A/Indonesia/5/2005) were boosted after the second immunization. However, there was no clear antigen dose response seen following the second immunization. In the antigen alone control group, the animals had low levels of antibody indicating that the non-adjuvanted A/Indonesia split antigen is poorly immunogenic at the dose used.
There was 88 to 100% survival in the active treatment groups that received any dose of A/Indonesia split antigen formulated with AS03 or half the volume of AS03. In contrast, in the antigen alone control group, 43% of the animals survived.
Although viable challenge virus was recovered (virus isolation on MDCK cells) from lung tissue or pharyngeal swabs in all treatment groups, the overall proportion of animals with detectable virus was reduced in vaccinees relative to non-adjuvanted controls. Frequencies of virus-positive animals were generally lower in vaccine groups receiving higher doses of antigen. In the antigen alone control group 100% of the animals had detectable virus in the lungs and pharynx.
Conclusion: In a ferret H5N1 heterologous challenge model, low doses of detergent-split antigen formulated with AS03 Adjuvant System elicited antibodies to the immunizing H5N1 virus. The adjuvanted A/Indonesia/5/2005 (Clade 2.1) vaccine conferred improved protection against an A/Hong Kong/156/1997 (Clade 0) challenge as assessed by increased survival and reduced frequency of virus isolation from the lower and upper respiratory tract, suggesting a potential role in the reduction of virus transmission. Additional studies are planned with low doses of this vaccine in the H5N1 heterologous challenge model with other drifted strains belonging to different H5N1 clades.
