Serum antibody titers in Balb/c mice after prime or boost with wild-type viruses as determined by hemagglutination inhibition and ELISA assays.

aEach group of mice primed (0 dpi) and boosted (21 dpi) intranasally with wild-type H1N1 influenza viruses.bELISA titers expressed as reciprocal of the highest dilution of pooled sera with an O.D. value of≥0.150 when tested against purified NA ectodomain of A/California/04/09.cPooled sera collected three weeks post prime or boost and tested for HI titers against wild-type A/Solomon/03/06.dPooled sera collected three weeks post prime or boost and tested for HI titers against wild-type A/California/04/09.ePooled sera tested for Ig titers against purified NA ectodomain of A/California/04/09.fMice primed with A/Tennessee/1-560/09 and boosted with PBS alone.