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The impact of conjugate vaccine on carriage of Haemophilus influenzae type b
M L Barbour1, R T Mayon-White, C Coles
1Department of Paediatrics, John Radcliffe Hospital, Headington, Oxford, United Kingdom.
Insights
Conjugate vaccines against Haemophilus influenzae type b (Hib) reduce acquisition and carriage in infants. This suggests herd immunity to Hib is primarily achieved by lowering initial pathogen acquisition.
Area of Science:
- Pediatrics
- Immunology
- Public Health
Background:
- Haemophilus influenzae type b (Hib) conjugate vaccines may impact nasopharyngeal colonization.
- Understanding Hib colonization dynamics is crucial for vaccine efficacy and public health strategies.
Purpose of the Study:
- To compare Hib colonization in infants receiving the PRP-T conjugate vaccine versus unvaccinated controls.
- To investigate the impact of conjugate vaccination on Hib acquisition and carriage within families.
Main Methods:
- A study involving 371 infants and their families, comparing vaccinated (PRP-T) and unvaccinated groups.
- Surveillance of Hib colonization at 6, 9, and 12 months, with follow-up of vaccinated Hib carriers.
Main Results:
- Hib acquisition was significantly lower in vaccinated infants compared to controls (P < .01).
- Overall Hib carriage was lower in vaccinees (1.5%) versus controls (6.3%) (P = .04).
- Vaccination did not rapidly terminate existing Hib carriage in carriers.
Conclusions:
- Conjugate vaccination may induce herd immunity by reducing initial Hib acquisition, rather than solely by eliminating existing carriage.
- Lower Hib carriage rates were observed in unvaccinated siblings of vaccinees, supporting a reduction in transmission.
Abstract:
Conjugate vaccines against Haemophilus influenzae type b (Hib) may modify Hib pharyngeal colonization. Hib colonization was compared in 371 infants and their families. In Oxfordshire, infants received PRP-T (polyribosylribitol phosphate conjugated to tetanus toxoid) and in Buckinghamshire they did not (controls). Infants were followed at 6, 9, and 12 months of age. Also, 6 unvaccinated Hib carriers were vaccinated and followed for 6 weeks. Hib acquisition was lower in vaccinees than controls (P < .01). During surveillance, 1.5% of vaccinees and 6.3% of controls carried Hib (P = .04). Among those with family Hib exposure, the carriage rates were 8.7% and 38.5% (P = .07), respectively. Hiv carriage rates were lower among vaccinees' unvaccinated siblings. Giving conjugate vaccine to a child carrying Hib did not rapidly terminate carriage. Thus, a primary means by which herd immunity to Hib is induced in a vaccinated population may be through reduction or delay in the initial acquisition of Hib.