A pilot study of the immune response to whole inactivated avian influenza H7N1 virus vaccine in mice.

Background: Highly pathogenic avian influenza (HPAI) outbreaks in domestic poultry bring humans into close contact with new influenza subtypes and represent a threat to human health. In 1999, an HPAI outbreak of H7N1 virus occurred in domestic poultry in Italy, and a wild-type virus isolate from this outbreak was chosen as a pandemic vaccine candidate.

Objectives: We conducted a pilot study to investigate the kinetics of the humoral immune response induced after immunisation with an egg grown whole inactivated H7N1 virus vaccine in BALB/c mice.

Methods: Mice were vaccinated with one or two doses of H7N1 vaccine (15 microg total protein) to investigate the influenza specific antibody secreting cell (IS-ASC) and serum antibody responses.

Results: After the first dose of vaccine, only IgM IS-ASC were detected in the spleen and bone marrow, whereas IgG, IgA and IgM IS-ASC were found after the second dose. Low antibody titres were detected after the first immunisation, whilst the second dose of vaccine significantly boosted the HI (range 128-512), neutralising and IgG antibody titres. The IgG subclass response was dominated by IgG2a indicating a dominant Th1 response after the first vaccination, whereas a more mixed Th1/Th2 profile was observed after the second dose.

Conclusions: This pilot study shows the value of using a number of immunological methods to evaluate the quality of the immune response to potential pandemic candidate vaccines.