XK and obesity due to melanocortin 4 receptor deficiency: Using a variety of different influenza virus antigens, including whole viruses, recombinant hemagglutinin (HA) proteins, and peptides that span the HA and neuraminidase (NA) proteins of the Cal09 strain, we found that the repertoire of antibodies raised against influenza viruses following previous vaccinations and/or natural exposures, referred to here as baseline immune history (BIH), and postvaccination responses were significantly different in individuals with obesity and healthy-weight controls, especially with regard to A/H1N1 influenza virus strains.