(A) Bars 1–8, in gray tones, correspond to absorbance signals from non-exposed subjects (samples taken from March to May 2008). Bar 9, in black, shows the average absorbance value of samples 1 to 8. Bars 10 to 14, shown in colour, correspond to absorbance signals from Influenza A/H1N1 negative subjects. Bars 15–23, shown in colour, correspond to absorbance signals from samples of Influenza A H1N1 positive subjects (diagnosed two or three weeks previously by RT-PCR). Error bars represent one standard deviation (B) Proper refolding (biorecognition of antibodies from a positive patient), was evaluated for 4 different production batches of HA63–286-RBD. Batch 5 is a reference batch where HA63–286-RBD was expressed in its soluble form using a signal peptide for periplasmic expression.