The infants will be followed-up and undergo venipuncture under aseptic precautions to withdraw 0.8-1.0 ml blood at five further visits viz. 3 months±2 weeks [corresponding to a visit for 2nd/3rd dose of diphtheria- pertussis- tetanus (DPT) vaccine and live oral poliovirus vaccine(OPV)], 6 months±2 weeks (corresponding to visit for 3rd dose of Hepatitis B at 6 months of age), 7.5 months ±2 weeks, at 9 months ±2 weeks (corresponding to visit for measles vaccine as per the current schedule), and at 12 ± 2 weeks months of age (corresponding to visit for routine follow-up).