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Recommendations of the Immunization Practices Advisory Committee Supplementary Statement: Change in Administration Schedule for Haemophilus b Conjugate Vaccines

In December 1989, the Food and Drug Administration licensed a new vaccine--Haemophilus b Conjugate Vaccine (Meningococcal Protein Conjugate) (PRP-OMP)--for routine use in children greater than or equal to 18 months of age. The license contains the statement that PRP-OMP can be given to children as young as 15 months of age when "it is expected that the child will not return at 18 months of age for Haemophilus b immunization." Since December 1989, two vaccines previously licensed for use in children at 18 months of age--Haemophilus b Conjugate Vaccine (Diphtheria Toxoid Conjugate) (PRP-D) and Haemophilus b Conjugate Vaccine (Diphtheria CRM 197 Protein Conjugate) (PRP-HbOC)--also have been approved for use in children as young as 15 months of age.

Some differences in immunogenicity may exist among different Haemophilus b conjugate vaccines (1). However, further studies are needed to confirm any differences and evaluate their clinical relevance. In addition, immunogenicity is age-dependent, with immune response improving with increasing age (Table 1).

Approximately 7% of all Haemophilus influenzae type b disease in children less than 5 years of age occurs in children 15-17 months of age. Because of the substantial immunogenicity of the Haemophilus b conjugate vaccines when given to children in this age group, the Immunization Practices Advisory Committee (ACIP) now recommends routine vaccination of children at 15 months instead of at 18 months of age using any of the Haemophilus b conjugate vaccines licensed for use. Prior ACIP recommendations for the use of PRP-D are applicable to the newer conjugate vaccines (2).


  1. Wenger JD, Ward JI, Broome CV. Prevention of Haemophilus influenzae type b disease: vaccines and passive prophylaxis. In: Remington JS, Swartz MN, eds. Current clinical topics in infectious diseases. Vol 10. Boston: Blackwell Scientific Publications, 1989:306-39.

  2. ACIP. Update: prevention of Haemophilus influenzae type b disease. MMWR 1988;37:13-6.

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