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Immunogenicity of Haemophilus influenzae type b capsular polysaccharide vaccines in 18-month-old infants
Insights
The Haemophilus influenzae vaccine PRP-D is more effective than PRP alone in inducing protective antibody levels in infants. Revaccination at 24 months is recommended for infants immunized younger than this age.
Area of Science:
- Pediatrics
- Immunology
- Vaccinology
Background:
- Haemophilus influenzae type b (Hib) infections pose a significant health risk to young children.
- The polyribosyl ribitol phosphate (PRP) polysaccharide antigen is the target for Hib vaccines.
- Developing effective vaccination strategies for infants is crucial for disease prevention.
Purpose of the Study:
- To compare the immunogenicity and efficacy of two Haemophilus influenzae vaccines: polyribosyl ribitol phosphate (PRP) and PRP conjugated to diphtheria toxoid (PRP-D).
- To evaluate the antibody response in infants aged 17 to 22 months receiving these vaccines concurrently with diphtheria-tetanus-pertussis boosters.
Main Methods:
- A study involving 94 healthy infants aged 17 to 22 months.
- Infants received either PRP or PRP-D vaccine simultaneously with a diphtheria-tetanus-pertussis booster, at separate injection sites.
- Anti-PRP antibody concentrations were measured before and after vaccination to assess immune response.
Main Results:
- Both PRP and PRP-D vaccines were generally well-tolerated, with similar systemic reactions and low rates of minor local reactions.
- PRP-D demonstrated significantly higher efficacy in inducing protective anti-PRP antibody levels compared to PRP in non-immune infants.
- In non-immune infants, 81% of PRP-D recipients achieved protective antibody levels (≥0.15 µg/mL) versus only 43% of PRP recipients.
Conclusions:
- The conjugate Haemophilus influenzae vaccine (PRP-D) is superior to the unconjugated polysaccharide vaccine (PRP) in eliciting protective immunity in infants.
- A substantial proportion of non-immune 18-month-old infants may not achieve adequate antibody levels with the PRP vaccine alone.
- Revaccination at 24 months of age is advisable for infants immunized at a younger age to ensure sustained protective immunity against Haemophilus influenzae.
Abstract:
Haemophilus influenzae vaccine containing polyribosyl ribitol phosphate (PRP) or PRP covalently linked to diphtheria toxoid (PRP-D) was given to 94 healthy infants 17 to 22 months of age at the same time, but not at the same site, as a diphtheria-tetanus-pertussis booster. Systemic reactions were similar in the two vaccine groups and resembled those expected with the diphtheria-tetanus-pertussis injection alone. Six (13%) and seven (14%) of the PRP and PRP-D recipients, respectively, had minor local reactions to the Haemophilus vaccine. Among the 77 children who were not already naturally immune (ie, anti-PRP antibody concentration of less than or equal to 0.15 micrograms of protein per milliliter) before vaccination, PRP-D was significantly more effective than PRP in inducing protective levels of antibody. Only 15 (43%) of the 35 nonimmune PRP recipients achieved a concentration of greater than or equal to 0.15 microgram/mL and only seven (20%) reached a concentration greater than or equal to 1.0 micrograms/mL following vaccination. In contrast, 34 (81%) of the 42 nonimmune recipients of PRP-D had a concentration of greater than or equal to 0.15 microgram/mL following vaccine and 32 (62%) had a concentration of greater than or equal to 1.0 micrograms/mL (P less than or equal to .001). These results suggest that more than one-half of nonimmune 18-month-old infants will not respond to PRP with protective levels of antibody. In light of the current data, recommendation for revaccination at 24 months of age for those immunized at any younger age is appropriate.