[Show abstract][Hide abstract] ABSTRACT: In recent years, several avian influenza subtypes (H5, H7 and H9) have transmitted directly from birds to man, posing a pandemic threat.
We have investigated the immunogenicity and protective efficacy of a cell based candidate pandemic influenza H7 vaccine in pre-clinical animal models.
Mice and ferrets were immunised with two doses of the split virus vaccine (12-24 microg haemagglutinin) with or without aluminium hydroxide adjuvant and challenged 3 weeks after second dose with the highly pathogenic A/chicken/Italy/13474/99 (H7N1) virus. The H7N1-specific serum antibody response was also measured. After challenge, viral shedding, weight loss, disease signs and death (only mice) were recorded.
Low-to-modest serum antibody titres were detected after vaccination. Nevertheless, the vaccine induced significant protection from disease after challenge with the wild-type virus. In the murine lethal challenge model, vaccination effectively prevented death and, furthermore, formulation with adjuvant reduced excessive weight loss and viral shedding. In ferrets, vaccination reduced viral shedding and protected against systemic spread of the virus.
We have extended to the H7 subtype the finding that protective efficacy may not be directly correlated with the pre-challenge levels of serum antibodies, a finding which could be of great importance in assessing the potential effectiveness of pandemic influenza vaccines.
Influenza and Other Respiratory Viruses 06/2009; 3(3):107-17. DOI:10.1111/j.1750-2659.2009.00082.x · 2.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Avian influenza H7 viruses have transmitted from poultry to man causing human illness and fatality, highlighting the need for pandemic preparedness against this subtype. We have developed and tested the first cell-based human vaccine against H7 avian influenza virus in a phase I clinical trial. Sixty healthy volunteers were intramuscularly vaccinated with two doses of split H7N1 virus vaccine containing 12 microg or 24 microg haemagglutinin alone or with aluminium hydroxide adjuvant (300 microg or 600 microg, respectively). The vaccine was well tolerated in all subjects and no serious adverse events occurred. The vaccine elicited low haemagglutination inhibition and microneutralisation titres, although the addition of aluminium adjuvant augmented the antibody response. We found a higher number of antibody secreting cells and an association with IL-2 production in subjects with antibody response. In conclusion, our study shows that producing effective H7 pandemic vaccines is as challenging as has been observed for H5 vaccines.
[Show abstract][Hide abstract] ABSTRACT: The threat of a new influenza pandemic has led to renewed interest in dose-sparing vaccination strategies such as intradermal immunization and the use of adjuvanted vaccines. In this study we compared the quality and kinetics of the serum antibody response elicited in mice after one or two immunizations with a split influenza A (H3N2) virus, using three different low-dose vaccination strategies. The mice were divided into four groups, receiving either a low-dose vaccine (3 microg hemagglutinin [HA]) intradermally or intramuscularly with or without aluminum adjuvant or the normal human vaccine dose (15 microg HA) intramuscularly. Sera were collected weekly after vaccination and tested in the hemagglutination inhibition, virus neutralization, and enzyme-linked immunosorbent assays. The antibody responses induced after intradermal or intramuscular low-dose vaccinations were similar and lower than those observed after the human vaccine dose. However, low-dose adjuvanted vaccine elicited a serum antibody response comparable to that elicited by the human dose, although the second immunization did not result in any increase in cross-reactive hemagglutination inhibition antibodies, and the peak serum antibody response was observed 1 week later than in the other vaccination groups. Our murine data suggest that the low-dose intradermal route does not show any obvious advantage over the low-dose intramuscular route in inducing a serum antibody response and that none of the low-dose vaccination strategies is as effective as intramuscular vaccination with the normal human dose. However, the low-dose aluminum-adjuvanted vaccine could present a feasible alternative in case of limited vaccine supply.
[Show abstract][Hide abstract] ABSTRACT: The spleen, bone marrow and lymph nodes are all known to be important organs for the initiation and maintenance of an immune response after vaccination. To investigate the differences and similarities in the humoral and cellular immune responses between these tissues, we vaccinated mice once or twice with the conventional human dose (15 microg HA) of influenza A (H3N2) split virus vaccine and analysed the sera and lymphocytes collected from the different sites. We found that the response of antibody secreting cells (ASC) in the lymph nodes appeared to be more transient than in the spleen, possibly because the influenza-specific IgM ASC in particular might have migrated from the lymph nodes immediately after activation. The serum antibody response was found to initially correspond with the ASC response elicited in the spleen and the lymph nodes, whereas the later serum IgG reflected the ASC response in the bone marrow. Proliferation of influenza-specific CD4(+) and CD8(+) cells was predominantly observed in the spleen and was associated with higher concentrations of cytokines than in the lymph nodes. The finding of influenza-specific CD8(+) cell proliferation in the spleen indicates that a split influenza virus vaccine may stimulate a cytotoxic T-cell response. Our results also showed that the primary response elicited a mixed Th1/Th2 profile, whereas the secondary response was skewed towards a Th2 type. Each of the three tissues had a different immunological pattern, suggesting that in preclinical vaccine studies, there is a case for investigating a range of immunological sites.