Clinical trials of the Haemophilus influenzae type b capsular polysaccharide-diphtheria toxoid conjugate vaccine
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1Department of Pediatrics, Albany Medical College, NY 12208.
Insights
The PRP-D vaccine demonstrates excellent safety and tolerability in over 3000 young children. This conjugate vaccine effectively induces protective antibody levels and immunologic memory in various age groups.
Area of Science:
- Immunology
- Vaccinology
- Pediatric Medicine
Background:
- The Haemophilus influenzae type b (Hib) polysaccharide vaccine (PRP) has limitations in inducing a robust immune response, particularly in infants.
- Conjugate vaccines, such as PRP-D, were developed to enhance immunogenicity by linking the polysaccharide to a carrier protein.
- Understanding the safety and immunogenicity profile of PRP-D is crucial for its effective implementation in pediatric vaccination schedules.
Purpose of the Study:
- To evaluate the safety and tolerability of the PRP-D vaccine in subjects under 2 years of age.
- To assess the immunogenicity of the PRP-D vaccine, including antibody response and the induction of immunologic memory.
- To compare the reaction rates of PRP-D with PRP and placebo vaccines.
Main Methods:
- Clinical trials involving over 3000 subjects under 2 years of age receiving one or more doses of PRP-D vaccine.
- Monitoring and comparison of local and systemic reactions between PRP-D recipients and those receiving PRP or placebo.
- Measurement of antibody levels (IgG, IgM) and assessment of recall response (immunologic memory) after vaccination.
Main Results:
- No statistically significant differences in local or systemic reactions were observed between PRP-D and control vaccine groups.
- The PRP-D vaccine is well-tolerated and not associated with clinically significant adverse reactions.
- PRP-D demonstrated T cell-dependent immunogenicity, with sequential antibody increases upon repeated immunization and a high IgG proportion. Immunologic memory was evident one year post-vaccination.
- Consistent immunogenicity across age groups: adults achieved >200 µg/ml antibody levels, infants 7-24 months achieved >1 µg/ml in >90% with 1-2 doses, and infants <7 months achieved ≥0.15 µg/ml in >90%.
Conclusions:
- The PRP-D vaccine is safe and well-tolerated in infants and young children.
- PRP-D is a consistently immunogenic vaccine, inducing protective antibody levels and long-lasting immunologic memory.
- The findings support the use of PRP-D as an effective vaccine for preventing diseases caused by Haemophilus influenzae type b.
Abstract:
To date in the United States over 3000 subjects under 2 years of age have received 1 or more doses of PRP-D vaccine. Thus far there have been no statistically significant differences between the rate of local or systemic reactions among recipients of this vaccine and that among those who received the PRP or placebo control vaccines. The vaccine is well-tolerated and is not associated with clinically significant adverse reactions. The PRP-D vaccine has been shown to be a T cell-dependent immunogen, inducing sequential increases in antibody level with repeated immunization and producing a high proportion of IgG relative to IgM. A recall response, or immunologic memory effect, has been demonstrated in children 1 year after receiving PRP-D. PRP-D is consistently immunogenic in all age groups. In adults this vaccine induces a geometric mean antibody response greater than 200 micrograms/ml. In infants 7 to 24 months of age levels greater than 1 microgram/ml have been achieved in over 90% of the subjects with 1 or 2 doses of PRP-D, whereas 90% or more of infants under 7 months of age achieve levels of 0.15 microgram/ml or greater.