designed to detect the sort of anti-HA2 stalk antibodies highlighted above in association with severe disease in vaccinated swine. Ultimately, therefore, we are unable to discern whether the rise in Ch+5 ELISA antibody in vaccinated animals suggests early crossreactive, non-neutralizing antibody to Apdm09 or further antibody increase to TIV antigens 4 weeks after their second dose although microarray indicates the latter certainly contributed. T-cell hypo-responsiveness may be an alternate explanation compatible with a hypothesis of direct vaccine effect. This phenomenon has been reported in same-season influenza vaccine booster-dose studies with parallels also in the allergy literature suggesting peptide-induced T-cell hypo-responsiveness beginning at 2�C8 weeks and lasting up to 40 weeks. However, while interferon-gamma was below detectable limits in both groups, lung cytokines in vaccinated Cefetamet pivoxil HCl ferrets were otherwise consistently higher compared to placebo animals at Ch+5, notably including the Th2 IL4, pro-inflammatory IL17 and regulatory IL10 cytokines. IL17 has been implicated as super-inducer of neutrophil infiltration and acute lung immuno-pathology following influenza infection, with counteractive dampening interactions by IL10. In an earlier Canadian ferret experiment in which animals Albaspidin-AA administered a single dose of 2008�C09 TIV also experienced worse Apdm09 illness, IL6 in nasal wash was substantially raised in the Fluviral group and IL10 significantly in the Flumist group, with disease enhancement suggested in both vaccine groups compared to controls. We did not assess nasal wash cytokines or Flumist and were not statistically powered to explore cytokine differences, but lung IL6 and IL10 were also both non-significantly raised at Ch+5 in our Fluviral versus placebo ferrets. All cytokine values were then lower at Ch+14 in the absence of lung pathology. However, none of the between-group cytokine differences at either time point were statistically significant. There are limitations to this study. Although ferrets are considered the ideal animal model for human influenza infection, there are anticipated differences in immunologic and clinical aspects of immunization, infection and illness responses across species. Overall patterns may be compared but ferret studies do not support precise quantification of actual risk in humans. The greater likelihood of more severe disease based on several clinical indicators among vaccinated compared to unvaccinated ferrets may not replicate the greater likelihood of medically-attended Apdm09 illness we previously reported in vaccinated humans. In using influenza-na? ��ve, systematically infected ferrets there are clear differences from the human experience with respect to pre-conditions, process, and other relevant parameters. Clinical relevance of the differences we report between vaccinated and placebo ferrets is ultimately best interpreted in the context of our study objectives assigned in follow up to the prior human observations we reported. The main objective of the ferret study was to assess through randomized, controlled design whether prior receipt of 2008�C09 TIV may have had direct, adverse effects on Apdm09 illness, specifically powered related to weight loss. Although we cannot more precisely elucidate the underlying mechanisms involved, the current ferret study supports the hypothesis of direct vaccine effect. Taken together with prior human and swine studies, these findings represent a signal that warrant further investigation and better understanding though they cannot be considered conclusive. The most prominent concern in this ferret study may relate to our failure to show neutralizing antibody response to vaccine, an issue we therefore consider in detail.