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Comparison of active and combined passive/active immunization of Navajo children against Haemophilus influenzae type
G W Letson1, M Santosham, R Reid
1Department of International Health, Johns Hopkins University School of Hygiene and Public Health, Baltimore, MD 21205.
Insights
A new Haemophilus influenzae type b conjugate vaccine (HbOC) showed low immunogenicity in 2-month-olds. However, a third dose at 6 months achieved protective antibody levels, with passive-active immunization maintaining protection without interfering with vaccine response.
Area of Science:
- Immunology
- Vaccinology
- Pediatrics
Background:
- Haemophilus influenzae type b (Hib) infections pose a significant risk, especially in high-risk populations.
- Early infant immunization is crucial for preventing Hib disease.
- Assessing novel vaccine strategies, including combined passive-active immunization, is vital for improving protection.
Purpose of the Study:
- To evaluate the immunogenicity of a new Haemophilus influenzae type b mutant-diphtheria toxic conjugate vaccine (HbOC).
- To compare the efficacy of HbOC alone versus simultaneous active (HbOC) and passive immunization with bacterial polysaccharide immunoglobulin.
- To determine if combined immunization interferes with the active immune response to subsequent vaccine doses.
Main Methods:
- A study involving a high-risk Navajo population compared HbOC immunogenicity with and without passive immunization.
- Infants received HbOC at 2, 4, and 6 months, with one group receiving bacterial polysaccharide immunoglobulin at 2 months.
- Antibody concentrations against Hib capsular polysaccharide were measured at different time points.
Main Results:
- A single HbOC dose at 2 months resulted in low antibody response (27%).
- After three doses (at 6 months), all infants achieved protective antibody levels (≥0.15 microgram/ml).
- Combined passive-active immunization at 2 months uniformly achieved protective levels by 4 months and did not impede the response to subsequent HbOC doses.
Conclusions:
- Combined passive-active immunization with bacterial polysaccharide immunoglobulin and HbOC at 2 months maintains protective antibody levels.
- This combined approach does not interfere with the active immune response to further HbOC vaccine doses at 4 and 6 months.
- HbOC vaccine requires multiple doses to achieve protective immunity in infants, but combined immunization can provide earlier protection.
Abstract:
In a high risk Navajo population we compared the immunogenicity of a new Haemophilus influenzae type b mutant-diphtheria toxic conjugate vaccine (HbOC) with simultaneous active (HbOC) and passive immunization with bacterial polysaccharide immunoglobulin prepared from adults immunized with H. influenzae b, pneumococcal and meningococcal vaccines. Only 7 of 26 (27%) 2-month-olds had an increase in H. influenzae b capsular polysaccharide antibody after a single dose of HbOC, a proportion similar to that of saline controls (9 of 25, 36%). After a second HbOC dose at 4 months 88% had antibody concentrations of 0.15 microgram or more, and after a third dose at 6 months all had antibody levels greater than or equal to 0.15 microgram/ml. The group receiving both HbOC and bacterial polysaccharide immunoglobulin at 2 months uniformly had H. influenzae b CP antibody concentrations of greater than or equal to 0.15 microgram/ml at 4 months (P less than 0.001 relative to "HbOC alone" group) and subsequently responded similarly to second and third doses of HbOC vaccine as did also the "HbOC alone" group. We conclude that combined passive/active immunization with bacterial polysaccharide immunoglobulin and HbOC at 2 months maintains antibody at concentrations thought to be protective (greater than or equal to 0.15 microgram/ml) without interfering with the active antibody response to second and third doses of HbOC at 4 and 6 months of age.