Vaccination against Hemophilus Influenza B

Haemophilus Influenza type B is a primary cause of severe bacterial infection in young infants, which begins at about 4-6 months of age after maternal antibodies have disappeared. Incidence rate in the United States is 100 / 100000 annually, in children under 5 years of age with 60% of them manifesting as meningitis with a case fatality rate of 3-5%. The exact incidence in developing countries is unknown but considered to be high with higher case fatality rate particularly in Africa.

The vaccine was prepared from the polysaccharide capsule, which is the chief T cell independent antigen. To make it T cell dependent, it was necessary to conjugate it with a

T dependent protein either with diphtheria toxin or meningococcus protein or tetanus toxoid.

The immunogenic nature of these vaccines varies according to the method of conjugation,

choice of carrier protein and weight of polysaccharide. Initially, conjugate vaccine was recommended only from 18 months of age. Since June 1991, Center for Disease Control has approved administration of the vaccine beginning at 2 months of age. Currently, 3 doses are recommended at 2 months interval during 1st year of life with a booster between 15 and 18 months of age. The vaccine is useful only during the first few years of life after which natural immunity due to cross-reaction with non-pathogenic strain takes over.