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Prior to the introduction of Haemophilus b Conjugate Vaccines, Haemophilus influenzae type b (Hib) was the most frequent cause of bacterial meningitis and a leading cause of serious, systemic bacterial disease in young children worldwide.1,2,3,4
Hib disease occurred primarily in children under 5 years of age in the United States prior to the initiation of a vaccine program and was estimated to account for nearly 20,000 cases of invasive infections annually, approximately 12,000 of which were meningitis. The mortality rate from Hib meningitis is about 5%. In addition, up to 35% of survivors develop neurologic sequelae including seizures, deafness, and mental retardation.5,6 Other invasive diseases caused by this bacterium include cellulitis, epiglottitis, sepsis, pneumonia, septic arthritis, osteomyelitis and pericarditis.
Prior to the introduction of the vaccine, it was estimated that 17% of all cases of Hib disease occurred in infants less than 6 months of age.7 The peak incidence of Hib meningitis occurs between 6 to 11 months of age. Forty-seven percent of all cases occur by one year of age with the remaining 53% of cases occurring over the next four years.2,20
Among children under 5 years of age, the risk of invasive Hib disease is increased in certain populations including the following:
- Daycare attendees8,9
- Lower socio-economic groups10
- Blacks11 (especially those who lack the Km(1) immunoglobulin allotype)12
- Caucasians who lack the G2m(n or 23) immunoglobulin allotype13
- Native Americans14,15,16
- Household contacts of cases17
- Individuals with asplenia, sickle cell disease, or antibody deficiency syndromes18,19
An important virulence factor of the Hib bacterium is its polysaccharide capsule (PRP). Antibody to PRP (anti-PRP) has been shown to correlate with protection against Hib disease.3,21 While the anti-PRP level associated with protection using conjugated vaccines has not yet been determined, the level of anti-PRP associated with protection in studies using bacterial polysaccharide immune globulin or nonconjugated PRP vaccines ranged from > 0.15 to > 1.0 mcg/mL.22-28
Nonconjugated PRP vaccines are capable of stimulating B-lymphocytes to produce antibody without the help of T-lymphocytes (T-independent). The responses to many other antigens are augmented by helper T-lymphocytes (T-dependent). PedvaxHIB is a PRP-conjugate vaccine in which the PRP is covalently bound to the OMPC carrier29 producing an antigen which is postulated to convert the T-independent antigen (PRP alone) into a T-dependent antigen resulting in both an enhanced antibody response and immunologic memory.
Clinical Evaluation of PedvaxHIB
PedvaxHIB, in a lyophilized formulation (lyophilized PedvaxHIB), was initially evaluated in 3,486 Native American (Navajo) infants, who completed the primary two-dose regimen in a randomized, double-blind, placebo-controlled study (The Protective Efficacy Study). At the time of the study, this population had a much higher incidence of Hib disease than the United States population as a whole and also had a lower antibody response to Haemophilus b Conjugate Vaccines, including PedvaxHIB.14,15,16,30,33
Each infant in this study received two doses of either placebo or lyophilized PedvaxHIB with the first dose administered at a mean of 8 weeks of age and the second administered approximately two months later; DTP and OPV were administered concomitantly. Antibody levels were measured in a subset of each group (TABLE 1).
Antibody Responses in Navajo Infants
|Vaccine|| No. of
|Time||% Subjects with|| Anti-PRP GMT
|> 0.15 mcg/mL||> 1.0 mcg/mL|
| * Post-Vaccination values obtained approximately 1-3 months
after each dose.
** The Protective Efficacy Study
† Immunogenicity Trial34
‡ Booster given at 12 months of age; Post-Vaccination values obtained 1 month after administration of booster dose.
Most subjects were initially followed until 15 to 18 months of age. During this time, 22 cases of invasive Hib disease occurred in the placebo group (8 cases after the first dose and 14 cases after the second dose) and only 1 case in the vaccine group (none after the first dose and 1 after the second dose). Following the primary two-dose regimen, the protective efficacy of lyophilized PedvaxHIB was calculated to be 93% with a 95% confidence interval of 57%-98% (p=0.001, two- tailed). In the two months between the first and second doses, the difference in number of cases of disease between placebo and vaccine recipients (8 vs. 0 cases, respectively) was statistically significant (p=0.008, two-tailed); however, a primary two-dose regimen is required for infants 2-14 months of age.
At termination of the study, placebo recipients were offered vaccine. All original participants were then followed two years and nine months from termination of the study. During this extended follow-up, invasive Hib disease occurred in an additional seven of the original placebo recipients prior to receiving vaccine and in one of the original vaccine recipients (who had received only one dose of vaccine). No cases of invasive Hib disease were observed in placebo recipients after they received at least one dose of vaccine. Efficacy for this follow-up period, estimated from person- days at risk, was 96.6% (95 C.I., 72.2-99.9%) in children under 18 months of age and 100% (95 C.I., 23.5-100%) in children over 18 months of age.33
Since protective efficacy with lyophilized PedvaxHIB was demonstrated in such a high risk population, it would be expected to be predictive of efficacy in other populations.
The safety and immunogenicity of lyophilized PedvaxHIB were evaluated in infants and children in other clinical studies that were conducted in various locations throughout the United States. PedvaxHIB was highly immunogenic in all age groups studied.31,32
Lyophilized PedvaxHIB induced antibody levels greater than 1.0 mcg/mL in children who were poor responders to nonconjugated PRP vaccines. In a study involving such a subpopulation,33,34 34 children ranging in age from 27 to 61 months who developed invasive Hib disease despite previous vaccination with nonconjugated PRP vaccines were randomly assigned to 2 groups. One group (n=14) was vaccinated with lyophilized PedvaxHIB and the other group (n=20) with a nonconjugated PRP vaccine at a mean interval of approximately 12 months after recovery from disease. All 14 children vaccinated with lyophilized PedvaxHIB but only 6 of 20 children re- vaccinated with a nonconjugated PRP vaccine achieved an antibody level of > 1.0 mcg/mL. The 14 children who had not responded to revaccination with the nonconjugated PRP vaccine were then vaccinated with a single dose of lyophilized PedvaxHIB; following this vaccination, all achieved antibody levels of > 1.0 mcg/mL.
In addition, lyophilized PedvaxHIB has been studied in children at high risk of Hib disease because of genetically-related deficiencies [Blacks who were Km(1) allotype negative and Caucasians who were G2m(23) allotype negative] and are considered hyporesponsive to nonconjugated PRP vaccines on this basis.35 The hyporesponsive children had anti-PRP responses comparable to those of allotype positive children of similar age range when vaccinated with lyophilized PedvaxHIB. All children achieved anti-PRP levels of > 1.0 mcg/mL.
The safety and immunogenicity of Liquid PedvaxHIB were compared with those of lyophilized PedvaxHIB in a randomized clinical study involving 903 infants 2 to 6 months of age from the general U.S. population. DTP and OPV were administered concomitantly to most subjects. The antibody responses induced by each formulation of PedvaxHIB were similar. TABLE 2 shows antibody responses from this clinical study in subjects who received their first dose at 2 to 3 months of age.
Antibody Responses to Liquid and Lyophilized PedvaxHIB in Infants From the General U.S. Population
|Time|| No. of
|% Subjects with anti-PRP|| Anti-PRP GMT
|> 0.15 mcg/mL||> 1.0 mcg/mL|
|(7.5 mcg PRP)||12-15||Prebooster||284||80||30||0.49|
|(15 mcg PRP)||12-15||Prebooster||87||71||28||0.39|
| * Approximately two months Post-Vaccination
** Approximately one month Post-Vaccination
A booster dose of PedvaxHIB is required in infants who complete the primary two-dose regimen before 12 months of age. This booster dose will help maintain antibody levels during the first two years of life when children are at highest risk for invasive Hib disease. (See TABLE 2 and DOSAGE AND ADMINISTRATION.)
In four United States studies, antibody responses to lyophilized PedvaxHIB were evaluated in several subpopulations of infants initially vaccinated between 2 to 3 months of age. (See TABLE 3.)
Antibody Responses* After Two Doses of Lyophilized PedvaxHIB Among Infants Initially Vaccinated at 2-3 Months of Age By Racial/Ethnic Group
|No. of Subjects||LYOPHILIZED||Anti-PRP GMT (mcg/mL)|
|% Subjects With Anti-PRP|
|> 0.15 mcg/mL||> 1.0 mcg/mL|
| * One month after the second dose
† Apache and Navajo
In two United States studies, antibody responses to Liquid PedvaxHIB were evaluated in several subpopulations of infants initially vaccinated between 2 to 3 months of age. (See TABLE 4.)
Antibody Responses* After Two Doses of Liquid PedvaxHIB Among Infants Initially Vaccinated at 2-3 Months of Age By Racial/Ethnic Group
|Racial/Ethnic Groups|| No. of
|LIQUID|| Anti-PRP GMT
|% Subjects With Anti-PRP|
|> 0.15 mcg/mL||> 1.0 mcg/mL|
| * One month after the second dose
** Apache and Navajo
Antibodies to the OMPC of N. meningitidis have been demonstrated in vaccinee sera, but the clinical relevance of these antibodies has not been established.33
Interchangeability of Licensed Haemophilus b Conjugate Vaccines and PedvaxHIB
Published studies have examined the interchangeability of other licensed Haemophilus b Conjugate Vaccines and PedvaxHIB.42,43,44,45,52 According to the American Academy of Pediatrics, excellent immune responses have been achieved when different vaccines have been interchanged in the primary series. If PedvaxHIB is given in a series with one of the other products licensed for infants, the recommended number of doses to complete the series is determined by the other product and not by PedvaxHIB. PedvaxHIB may be interchanged with other licensed Haemophilus b Conjugate Vaccines for the booster dose.52
Use with Other Vaccines
Results from clinical studies indicate that Liquid PedvaxHIB can be administered concomitantly with DTP, OPV, eIPV (enhanced inactivated poliovirus vaccine), VARIVAX* [Varicella Virus Vaccine Live (Oka/Merck)], M-M-R* II (Measles, Mumps, and Rubella Virus Vaccine Live) or RECOMBIVAX HB* [Hepatitis B Vaccine (Recombinant)].33 No impairment of immune response to individual tested vaccine antigens was demonstrated.
The type, frequency and severity of adverse experiences observed in these studies with PedvaxHIB were similar to those seen when the other vaccines were given alone.
In addition, a PRP-OMPC-containing product, COMVAX* [Haemophilus b Conjugate (Meningococcal Protein Conjugate) and Hepatitis B (Recombinant) Vaccine], was given concomitantly with a booster dose of DTaP [diphtheria, tetanus, acellular pertussis] at approximately 15 months of age, using separate sites and syringes for injectable vaccines. No impairment of immune response to these individually tested vaccine antigens was demonstrated. COMVAX has also been administered concomitantly with the primary series of DTaP to a limited number of infants. PRP antibody responses are satisfactory for COMVAX, but immune responses are currently unavailable for DTaP (see Manufacturer's Product Circular for COMVAX). No serious vaccine-related adverse events were reported.33
1. Cochi, S. L., et al: Immunization of U.S. children with Haemophilus influenzae type b polysaccharide vaccine: A cost- effectiveness model of strategy assessment. JAMA 253: 521-529, 1985.
2. Schlech, W. F., III, et al: Bacterial meningitis in the United States, 1978 through 1981. The National Bacterial Meningitis Surveillance Study. JAMA 253: 1749-1754, 1985.
3. Peltola, H., et al: Prevention of Haemophilus influenzae type b bacteremic infections with the capsular polysaccharide vaccine. N Engl J Med 310: 1561-1566, 1984.
4. Cadoz, M., et al: Etude epidemiologique des cas de meningitis purulentes hospitalises a Dakar pendant la decemie 1970-1979. Bull WHO 59: 575-584, 1981.
5. Sell, S. H., et al: Long-term Sequelae of Haemophilus influenzae meningitis. Pediatr 49: 206-217, 1972.
6. Taylor, H. G., et al: Intellectual, neuropsychological, and achievement outcomes in children six to eight years after recovery from Haemophilus influenzae meningitis. Pediatr 74: 198-205, 1984.
7. Hay, J. W., et al: Cost-benefit analysis of two strategies for prevention of Haemophilus influenzae type b infection. Pediatr 80(3): 319-329, 1987.
8. Redmond, S. R., et al: Haemophilus influenzae type b disease: an epidemiologic study with special reference to daycare centers. JAMA 252: 2581-2584, 1984.
9. Istre, G. R., et al: Risk factors for primary invasive Haemophilus influenzae disease: increased risk from daycare attendance and school age household members. J Pediatr 106: 190-195, 1985.
10. Fraser, D.W., et al: Risk factors in bacterial meningitis: Charleston County, South Carolina. J Infect Dis 127: 271-277, 1973.
11. Tarr, P. I., et al: Demographic factors in the epidemiology of Haemophilus influenzae meningitis in young children. J Pediatr 92: 884-888, 1978.
12. Granoff, D. M., et al: Response to immunization with Haemophilus influenzae type b polysaccharide-pertussis vaccine and risk of Haemophilus meningitis in children with Km(1) immunoglobulin allotype. J Clin Invest 74: 1708-1714, 1984.
13. Ambrosino, D. M., et al: Correlation between G2m(n) immunoglobulin allotype and human antibody response and susceptibility to polysaccharide encapsulated bacteria. J Clin Invest 75: 1935-1942, 1985.
14. Coulehan, J. L, et al: Epidemiology of Haemophilus influenzae type b disease among Navajo Indians. Pub Health Rep 99: 404-409, 1984.
15. Losonsky, G. A., et al: Haemophilus influenzae disease in the White Mountain Apaches: molecular epidemiology of a high risk population. Pediatr Infect Dis J 3: 539-547, 1985.
16. Ward, J. I., et al: Haemophilus influenzae disease in Alaskan Eskimos: characteristics of a population with an unusual incidence of disease. Lancet 1: 1281-1285, 1981.
17. Ward, J. I., et al: Haemophilus influenzae meningitis: a national study of secondary spread in household contacts. N Engl J Med 301: 122-126, 1979.
18. Ward, J., et al: Haemophilus influenzae bacteremia in children with sickle cell disease. J Pediatr 88: 261-263, 1976.
19. Bartlett, A. V., et al: Unusual presentations of Haemophilus influenzae infections in immunocompromised patients. J Pediatr 102: 55-58, 1983.
20. Recommendations of the Immunization Practices Advisory Committee. Polysaccharide vaccine for prevention of Haemophilus influenzae type b disease. MMWR 34(15): 201-205, 1985.
21. Santosham, M., et al: Prevention of Haemophilus influenzae type b infections in high-risk infants treated with bacterial polysaccharide immune globulin. N Engl J Med 317: 923-929, 1987.
22. Siber, G. R., et al: Preparation of human hyperimmune globulin to Haemophilus influenzae b, Streptococcus pneumoniae, and Neisseria meningitidis. Infect Immun 45: 248-254, 1984.
23. Smith, D. H., et al: Responses of children immunized with the capsular polysaccharide of Haemophilus influenzae type b. Pediatr 52: 637-645, 1973.
24. Robbins, J. B., et al: Quantitative measurement of 'natural' and immunization-induced Haemophilus influenzae type b capsular polysaccharide antibodies. Pediatr Res 7: 103-110, 1973.
25. Kaythy, H., et al: The protective level of serum antibodies to the capsular polysaccharide of Haemophilus influenzae type b. J Infect Dis 147: 1100, 1983.
26. Peltola, H., et al: Haemophilus influenzae type b capsular polysaccharide vaccine in children: a double-blind field study of 100,000 vaccinees 3 months to 5 years of age in Finland. Pediatr 60: 730-737, 1977.
27. Ward, J. I., et al: Haemophilus influenzae type b vaccines: Lessons For the Future. Pediatr 81: 886-893, 1988.
28. Daum, R. S., et al: Haemophilus influenzae type b vaccines: Lessons From the Past. Pediatr 81: 893-897, 1988.
29. Marburg, S., et al: Bimolecular chemistry of macromolecules: Synthesis of bacterial polysaccharide conjugates with Neisseria meningitidis membrane protein. J Am Chem Soc 108: 5282-5287, 1986.
30. Letson, G. W., et al: Comparison of active and combined passive/active immunization of Navajo children against Haemophilus influenzae type b. Pediatr Infect Dis J 7(111): 747-752, 1988.
31. Einhorn, M. S., et al: Immunogenicity in infants of Haemophilus influenzae type b polysaccharide in a conjugate vaccine with Neisseria meningitidis outer-membrane protein. Lancet 2: 299-302, 1986.
32. Ahonkhai, V.I., et al: Haemophilus influenzae type b Conjugate Vaccine (Meningococcal Protein Conjugate) (PedvaxHIB TM): Clinical Evaluation. Pediatr 85(4): 676-681, 1990.
33. Data on file at Merck Research Laboratories.
34. Granoff, D. M., et al: Immunogenicity of Haemophilus influenzae type b polysaccharide-outer membrane protein conjugate vaccine in patients who acquired Haemophilus disease despite previous vaccination with type b polysaccharide vaccine. J. Pediatr. 114(6): 925-933, June 1989.
35. Lenoir, A. A., et al: Response to Haemophilus influenzae type b (H. influenzae type b) polysaccharide N. meningitidis outer membrane protein (PS-OMP) conjugate vaccine in relation to Km(1) and G2m(23) allotypes. Twenty-sixth Interscience Conference on Antimicrobial Agents and Chemotherapy (Abstract #216) 133, 1986.
42. Recommendations of the Immunization Practices Advisory Committee. Recommendations for use of Haemophilus b Conjugate Vaccines and a combined diphtheria, tetanus, pertussis, and Haemophilus b vaccine. MMWR 42(RR-13): 1-15, 1993.
43. Daum, R. S., et al: Interchangeability of Haemophilus influenzae type b vaccines for the primary series (mix and match): a preliminary analysis [Abstract 976]. Pediatr Res 33: 166A, 1993.
44. Greenberg, D. P., et al: Enhanced antibody responses in infants given different sequences of heterogenous Haemophilus influenzae type b Conjugate Vaccines. J Pediatr 126: 206-211, 1995.
45. Anderson, E. L., et al: Interchangeability of Conjugated Haemophilus influenzae type b Vaccines in Infants. JAMA 273: 849-853, 1995.
52. American Academy of Pediatrics. Recommended Childhood Immunization Schedule - United States, January- December 1998. Pediatr 101(1): 154-157, 1998.
Last reviewed on RxList: 12/19/2007
This monograph has been modified to include the generic and brand name in many instances.
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