Related Experiment Videos
Study of booster doses of two Haemophilus influenzae type b conjugate vaccines including their interchangeability
D Scheifele1, B Law, L Mitchell
1Vaccine Evaluation Center, BC's Children's Hospital, Vancouver, Canada.
Insights
Booster immunization with Haemophilus influenzae type b (Hib) conjugate vaccines is effective in 18-month-olds. Even when switching vaccine types, children showed strong responses, but low pre-booster antibody levels correlated with weaker responses.
Area of Science:
- Immunology
- Pediatrics
- Vaccinology
Background:
- Primary immunization with Haemophilus influenzae type b (Hib) conjugate vaccines (HbOC or PRP-T) is standard for infants.
- Assessing booster responses and interchangeability of Hib vaccines is crucial for maintaining immunity.
Purpose of the Study:
- To evaluate booster immunization responses to Haemophilus influenzae type b (Hib) conjugate vaccines in 18-month-olds.
- To assess the interchangeability of different Hib vaccine products as boosters.
Main Methods:
- A prospective, randomized, evaluator-blinded study involving 319 children at two centers.
- Sera were analyzed for anti-PRP antibody levels before and 4 weeks after booster vaccination using an IgG-specific enzyme immunoassay.
Main Results:
- Most children responded robustly to booster vaccination, regardless of the primary vaccine or interchangeability.
- Pre-immunization anti-PRP antibody levels were low in a significant proportion of children (47% for HbOC, 35% for PRP-T).
- Children with undetectable pre-booster antibodies showed weaker responses post-vaccination.
Conclusions:
- Booster immunization with Hib conjugate vaccines is immunogenic in 18-month-olds, with no detrimental effects from product interchangeability.
- Low pre-booster antibody levels may indicate a need for earlier booster vaccination or alternative strategies.
- Further studies on long-term antibody levels and vaccine efficacy are recommended due to response heterogeneity.
Abstract:
A prospective, two center study of 319 children was undertaken to assess responses to booster immunization in healthy 18-month-olds who completed primary immunization 12 months earlier with Haemophilus influenzae type b (Hib) conjugate vaccine (either HbOC or PRP-T). Interchangeability of these products as boosters was also assessed, using combination products containing diphtheria, pertussis and tetanus components. The study was randomized and evaluator blinded. Sera obtained prior to booster vaccination and 4 weeks later were tested for anti-PRP using an IgG-specific enzyme immunoassay. Pre-immunization anti-PRP levels were low: unmeasurable levels (< 0.06 microgram ml-1) were present in 47% of those primed with HbOC and 35% of those primed with PRP-T (P < 0.05). Most children responded strongly to booster vaccination. Interchanging the products had no detrimental effect. Children who lacked measurable antibody prior to re-vaccination had significantly weaker responses 4 weeks afterward. Earlier Hib booster vaccination should be considered in Canada to avoid low anti-PRP trough levels. Extended follow-up of antibody levels and vaccine protective efficacy is also advisable given the observed heterogeneity of responses to booster vaccination.