We previously demonstrated the immunogenicity and tolerability of the serogroup 
B meningococcal vaccine, 4CMenB (Bexsero), in 11-17 y-olds randomized to receive 
1, 2, or 3 doses at 1, 2, or 6 mo intervals. Participants in this extension 
study provided an additional blood sample 18-24 mo after last vaccine dose, to 
assess persistence of serum bactericidal activity with human complement (hSBA), 
and to compare with age-matched 4CMenB-naïve controls. In the original study, 
one month after one 4CMenB dose, 93% of subjects had seroprotective hSBA titers 
(≥4) against indicator serogroup B strains for individual vaccine antigens 
(fHbp, NadA and NZOMV), increasing to ~100% after two or three doses. After 
18-24 mo, 62-73% of subjects given one dose had titers ≥4 against the three 
antigens, significantly lower rates than after two (77-94%) or three (86-97%) 
doses. Only proportions with titers ≥ 4 against NZOMV were significantly 
different between the two (77%) and three (90%, p < 0.0001) dose groups. These 
results confirm that two doses of 4CMenB, administered 1 to 6 mo apart, provide 
good levels of bactericidal activity against serogroup B meningococci, which 
were sustained at least 18-24 mo in over 64% of adolescents for all three tested 
vaccine-related antigens.