Safety and immunogenicity of two Haemophilus influenzae type b conjugate vaccines

Objectives. Haemophilus influenzae type b (Hib) infection remains a major public health problem in the developing world. We evaluated the safety and immunogenicity of a new PRP-CRM197 conjugate Hib vaccine (Vaxem Hib, Chiron Vaccines), compared with the HibTITER vaccine (Wyeth-Lederle Vaccines), following the World Health Organisation (WHO)'s accelerated schedule which allows 4-week intervals between doses. Study design. A phase II, observer-blind, multicentre, randomised, controlled, non-inferiority study. Methods. In total, 331 babies were immunised with either Vaxem Hib (N = 167) or Hib (N = 164) vaccine at 6, 10 and 14 weeks of age, in parallel with oral polio, diphtheriatetanus-pertussis and hepatitis B vaccines. Post-immunisation reactions were recorded after each immunisation and at follow-up visits. Anti-polyribosylribitol phosphate (PRP) antibodies were measured using enzyme-linked immunosorbent assays (ELISAs) before and 1 month after the third immunisation. Results. Overall, there was no significant difference in the anti-PRP levels between the two groups. One month after the third immunisation, 76% of vaccines in the Vaxem Hib group and 70% in the HibTITER group had anti-PRP antibody titres ≥ 1.0 μg/ml, while 96% of the Vaxem Hib group and 90% of the HibTITER group demonstrated anti-PRP antibody titres ≥ 0.15 μg/ml. The geometric mean titre at day 90 was 3.77 μg/ml for the Vaxem Hib and 3.0 μg/ml for the HibTITER groups. Although the Vaxem Hib vaccine produced more redness (6% versus 1%; p = 0.006) and swelling (5% versus 1%, p = 0.037), overall it was well tolerated compared with the HibTITER vaccine. There was no significant difference in vaccine-related elevated temperature (≥ 38°C) between the two groups (p = 0.11). Conclusion. Both vaccines showed comparable safety and immunogenicity profiles when administered to South African babies at 6, 10 and 14 weeks of age.