At week 28 in the 10 ( 9 ) , 10 ( 10 ) , and 10 ( 11 ) vp 3-dose groups , geometric mean EnvA enzyme-linked immunosorbent assay titers were 5721 , 10 929 , and 3420 , respectively , and Ad48 nAb titers were a median of 1.7-fold higher than for Ad5 .