Serum antibody titers in Balb/c mice after priming with reverse genetic 7+1 NA recombinant viruses as determined by hemagglutination inhibition and ELISA assays.

aEach group of mice primed intranasally with 7+1 recombinant 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.cRecombinant viruses with 7 gene segments from PR8 and the NA segment from the indicated H1N1 or H3N2 influenza A strain.dPooled sera tested for HI titers against rg PR8.ePooled sera tested for HI titers against wild-type A/California/04/09.fPooled sera tested for Ig titers against purified NA ectodomain of A/California/04/09.gMice primed with PBS alone.hPooled convalescent sera from Balb/c mice infected with wild-type A/California/04/09.