Haemophilus influenzae type b vaccine in India: need and timing, immunogenecity and tolerance.

Objective: (i) To assess the natural immunity and susceptibility to Haemophilus influenzae type b (Hib) infections in children in India. (ii) To study the immunogenecity and tolerance of Hib vaccine (ACTHIB) in young infants. Designs: (i) Cross sectional study. (ii) Prospective trial. Setting: Well baby and immunization clinics. Methods: (i) PRP antibody titers against Hib estimated in 172 healthy infants and children aged 1 month to 10 years. (ii) Antibody titres estimated before and after ACTHIB vaccine given with primary immunization (age group 6 to 8 weeks) in 50 babies. Results: (i) Naturally protective levels of Hib antibodies found in less than 20% of infants under one year, but in over 80% above 4 years. (ii) seroconversion after ACTHIB vaccination was 100% with very high protective levels. There were no significant adverse reactions. Conclusions: ACTHIB vaccine proved to be safe and highly immunogenic. As susceptibility to Hib is highest in the first year of life, the vaccine should be recommended in the primary immunization schedule (combined with DPT). The very high titers achieved suggest the possibility of decreasing the number of doses or the amount of antigen to reduce the prevalent high cost.