Immune response in infants aged 6-8 weeks was lower than that in older participants and , 6 months after third vaccination , antibody concentrations were significantly higher than pre-vaccination concentrations in Filipino ( 21 U/mL [ 16-28 ] vs 2.88 U/mL [ 1.95-4 .25 ] ) , but not Pakistani ( 3.76 U/mL [ 2.77-5 .08 ] vs 2.77 U/mL [ 2.1-3 .66 ] ) , infants .