For several decades Haemophilus influenzae type b (Haemophilus b) was
the most common cause of invasive bacterial disease, including meningitis, in
young children in the United States. Although nonencapsulated H. influenzae
are common and six capsular polysaccharide types are known, strains with the
type b capsule caused most of the invasive Haemophilus diseases.3
Haemophilus b diseases occurred primarily in children under 5 years of age
prior to immunization with Haemophilus influenzae type b vaccines. In
the US, the cumulative risk of developing invasive Haemophilus b disease during
the first 5 years of life was estimated to be about 1 in 200. Approximately
60% of cases were meningitis. Cellulitis, epiglottitis, pericarditis, pneumonia,
sepsis, or septic arthritis made up the remaining 40%. An estimated 12,000 cases
of Haemophilus b meningitis occurred annually prior to the routine use of conjugate
vaccines in toddlers.3,4 The mortality rate can be 5%, and neurologic
sequelae have been observed in up to 38% of survivors.5
The incidence of invasive Haemophilus b disease peaks between 6 months and
1 year of age, and approximately 55% of disease occurs between 6 and 18 months
of age.3 Interpersonal transmission of Haemophilus b occurs and risk
of invasive disease is increased in children younger than 4 years of age who
are exposed in the household to a primary case of disease. Clusters of cases
in children in day care have been reported and recent studies suggest that the
rate of secondary cases may also be increased among children exposed to a primary
case in the daycare setting.3,6
The incidence of invasive Haemophilus b disease is increased in certain children,
such as those who are native Americans, black, or from lower socioeconomic status,
and those with medical conditions such as asplenia, sickle cell disease, malignancies
associated with immunosuppression, and antibody deficiency syndromes.3,4,6
The protective activity of antibody to Haemophilus b polysaccharide was demonstrated
by passive antibody studies in animals and in children with agammaglobulinemia
or with Haemophilus b disease7 and confirmed with the efficacy study
of Haemophilus b polysaccharide (HbPs) vaccine.8 Data from passive
antibody studies indicate that a preexisting titer of antibody to HbPs of 0.15
µg/mL correlates with protection.9 Data from a Finnish field
trial in children 18 to 71 months of age indicate that a titer of > 1.0 µg/mL
3 weeks after vaccination is associated with long-term protection.10,11
Linkage of Haemophilus b saccharides to a protein such as CRM197
converts the saccharide (HbO) to a T-dependent (HbOC) antigen, and results in
an enhanced antibody response to the saccharide in young infants that primes
for an anamnestic response and is predominantly of the IgG class.12
Laboratory evidence indicates that the native state of the CRM197
protein and the use of oligosaccharides in the formulation of HibTITER (diphtheria crm197 protein conjugate) enhances
Prior to licensure, the immunogenicity of HibTITER (diphtheria crm197 protein conjugate) was evaluated in US infants
and children.15 Infants 1 to 6 months of age at first immunization
received three doses at approximately 2-month intervals.16 Children
7 to 11 and 12 to 14 months of age received 2 doses at the same interval.15
Children 15 to 23 months of age received a single dose.17 HibTITER (diphtheria crm197 protein conjugate)
was highly immunogenic in all age groups studied, with 97% to 100% of 1,232
infants attaining titers of ≥ 1 µg/mL and 92% to 100% for bactericidal
Long-term persistence of the antibody response was observed. More than 80%
of 235 infants who received three doses of vaccine had an anti-HbPs antibody
level ≥ 1 µg/mL at 2 years of age.18
The vaccine generated an immune response characteristic of a protein antigen.
IgG anti-HbPs antibodies of IgG1 subclass predominated and the immune system
was primed for a booster response to HibTITER (diphtheria crm197 protein conjugate) . There is some evidence suggesting
natural increases in antibody levels over time after vaccination, most probably
the result of contact with Haemophilus type b organisms or cross-reactive antigens.18
These studies were carried out at a time when significant levels of Haemophilus
b disease were still present in the community.
Antibody generated by HibTITER (diphtheria crm197 protein conjugate) has been found to have high avidity, a measure
of the functional affinity of antibody to bind to antigen. High-avidity antibody
is more potent than low-avidity antibody in serum bactericidal assays.19
The contribution to clinical protection is unknown.
Immunogenicity of HibTITER (diphtheria crm197 protein conjugate) was evaluated in 26 children 22 months to 5 years
of age who had not responded to earlier vaccination with Haemophilus b polysaccharide
vaccine. One dose of HibTITER (diphtheria crm197 protein conjugate) was immunogenic in all 26 children and generated
titers of ≥ 1 µg/mL in 25 of the 26 infants.20 HibTITER (diphtheria crm197 protein conjugate)
has been found to be immunogenic in children with sickle cell disease, a condition
that may cause increased susceptibility to Haemophilus b disease.21
HibTITER (diphtheria crm197 protein conjugate) has also been shown to be immunogenic in native American infants, such
as the group of 50 studied in Alaska who received three doses at 2, 4, and 6
months of age.20 Antibody levels achieved were comparable to those
seen in healthy US infants who received their first dose at 1 to 2 months of
age and subsequent doses at 4 to 6 months of age.15,16,20
Postlicensure surveillance of immunogenicity was conducted during the distribution
of the first 30 million doses of HibTITER (diphtheria crm197 protein conjugate) and during the time period over which
Haemophilus b disease in children has been decreasing significantly in areas
of extensive vaccine usage.20,22–29 After three doses, titers ranged
from 2.37 to 8.45 µg/mL with 67% to 94% attaining ≥ 1 µg/mL.20,24,25
Persistence of antibody was examined in several cohorts of subjects that received
either a selected commercial lot or that were part of the initial efficacy trial
in northern California. Geometric mean titers for these cohorts were between
0.51 and 1.96 just prior to boosting at 15 to 18 months. These lots not only
induced persistent antibody but also provided effective priming for a booster
dose with commercial lots, with postboosting titers greater than 1.0 µg/mL
in 80% to 97% of subjects.20
HibTITER (diphtheria crm197 protein conjugate) (HbOC) was shown to be effective in a large-scale controlled clinical
trial in a multiethnic population in northern California carried out between
February 1988 and June 1990.30,31 There were no (0) vaccine failures
in infants who received three doses of HibTITER (diphtheria crm197 protein conjugate) and 12 cases of Haemophilus
b disease (6 cases of meningitis) in the control group. The estimate of efficacy
is 100% (P= .0002) with 95% confidence intervals of 68% to 100%. Through the
end of 1991, with an additional 49,000 person-years of follow-up, there were
still no cases of Haemophilus b disease in fully vaccinated infants less than
2 years of age.22,23 One case of disease has been reported in a 3
1/2-year-old child who did not receive a booster dose as recommended.
A comparative clinical trial was performed in Finland where approximately 53,000
infants received HibTITER (diphtheria crm197 protein conjugate) at 4 and 6 months of age and a booster dose at 14
months in a trial conducted from January 1988 through December 1990. Only two
children developed Haemophilus b disease after receiving the two-dose primary
immunization schedule. One child became ill at 15 months of age and the other
at 18 months of age; neither child received the scheduled booster at 14 months
of age. No vaccine failure has been reported in children who received the two-dose
primary series and the booster dose at 14 months of age. Based on more than
32,000 person-years of follow-up time, the estimate of efficacy is about 95%
when compared to historical control groups followed between 1985 and 1988.20
Historical controls were used since all infants received one of two Haemophilus
b conjugate vaccines during the period of the trial.
Evidence of efficacy postlicensure includes significant reductions in Haemophilus
b disease that are closely associated with increases in the net doses of Haemophilus
b Conjugate Vaccine distributed in the US.20,22–29 In the northern
California Kaiser Permanente there has been a 94% decrease in Haemophilus disease
incidence in 1991 for children younger than 18 months of age, compared to 1984-1988,
when HibTITER (diphtheria crm197 protein conjugate) was not available for this age group.22,23 Furthermore,
active surveillance by the Centers for Disease Control and Prevention (CDC)
has shown a 71% decrease in Haemophilus b disease in children less than 15 months
old, between 1989 and 1991, which corresponds temporally and geographically
with increases in net doses of
Haemophilus b conjugate vaccine distributed in the US.26 As with
all vaccines, this conjugate vaccine cannot be expected to be 100% effective.
There have been rare reports to the Vaccine Adverse Event Reporting System (VAERS)
of Haemophilus b disease following full primary immunization.
3. Wenger JD, Ward JL, Broome CV. Prevention of Haemophilus influenzae
type b disease: vaccines and passive prophylaxis. In: Remington JS, Swartz MS,
eds. Current Clinical Topics in Infectious Diseases. New York, NY: McGraw-Hill
Inc; 1989;10: 306-339.
4. Recommendation of the Immunization Practices Advisory Committee (ACIP) –
polysaccharide vaccine for prevention of Haemophilus influenzae type
b disease. MMWR. 1985;34:201-205.
5. Sell SH. Long term sequelae of bacterial meningitis in children. Pediatr
Infect Dis J. 1983;2:90-93.
6. Broome CV. Epidemiology of Haemophilus influenzae type b infections
in the United States. Pediatr Infect Dis J. 1987;6:779-782.
7. Alexander HE. The productive or curative element in type b Haemophilus
influenzae rabbit serum. Yale J Biol Med. 1944;16:425-434.
8. Peltola H, Kayhty H, Sivonen A. 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. Pediatrics. 1977;60:730-737.
9. Robbins JB, Parke JC Jr, Schneerson R. Quantitative measurement of “natural”
and immunization-induced Haemophilus influenzae type b capsular polysaccharide
antibodies. Pediatr Res. 1973;7:103-110.
10. Kayhty H, Peltola H, Karanko V, et al. The protective level of serum antibodies
to the capsular polysaccharide of Haemophilus influenzae type b. J
Infect Dis. 1983;147:1100.
11. Kayhty H, Karanko V, Peltola H, et al. Serum antibodies after vaccination
with Haemophilus influenzae type b capsular polysaccharide and responses
to reimmunization: no evidence immunologic tolerance or memory. Pediatrics.
12. Weinberg GA, Granoff DM. Polysaccharide-protein conjugate vaccines for
the prevention of Haemophilus influenzae type b disease. J Pediatr.
13. Makela O, Péterfy F, Outshoorn IG, et al. Immunogenic properties of a (1-6)
dextran, its protein conjugates, and conjugates of its breakdown products in
mice. Scand J Immunol. 1984;19:541-550.
14. Anderson P, Pichichero ME, Insel RA. Immunogens consisting of oligosaccharides
from Haemophilus influenzae type b coupled to diphtheria toxoid or the
toxin protein CRM197. J Clin Invest. 1985;76:52-59.
15. Madore DV, Phipps DC, Eby R, et al. Immune response of young children vaccinated
with Haemophilus influenzae type b conjugate vaccines. In: Cruse JM,
Lewis RE, eds. Contributions to Microbiology and Immunology: Conjugate Vaccines.
New York, NY: Karger Medical and Scientific Publishers; 1989;10:125-150.
16. Madore DV, Phipps DC, Eby R, et al. Safety and immunologic response to
Haemophilus influenzae type b oligosaccharide-CRM197 conjugate
vaccine in 1- to 6-month-old infants. Pediatrics. 1990;85:331-337.
17. Madore DV, Johnson CL, Phipps DC, et al. Safety and immunogenicity of Haemophilus
influenzae type b oligosaccharide-CRM197 conjugate vaccine in
infants aged 15-23 months. Pediatrics. 1990;86:527-534.
18. Rothstein EP, Madore DV, Long S. Antibody persistence four years after
primary immunization of infants and toddlers with Haemophilus influenzae
type b CRM197 conjugate vaccine. J Pediatr. 1991; 119:655-657.
19. Schlesinger Y, Granoff DM. Avidity and bactericidal activity of antibodies
elicited by different Haemophilus influenzae type b conjugate vaccines.
20. Unpublished data available from Lederle Laboratories.
21. Gigliotti F, Feldman S, Wang WC, et al. Immunization of young infants with
sickle cell disease with a Haemophilus influenzae type b saccharide-diphtheria
CRM197 protein conjugate vaccine. J Pediatr. 1989;114:1006-1010.
22. Black SB, Shinefield HR, The Kaiser Permanente Pediatric Vaccine Study
Group. Immunization with oligosaccharide conjugate Haemophilus influenzae
type b (HbOC) vaccine on a large health maintenance organization population:
extended follow-up and impact on Haemophilus influenzae disease epidemiology.
Pediatric Infect Dis J. 1992;11:610-613.
23. Black SB, Shinefield HR, Fireman B, et al. Safety, immunogenicity, and
efficacy in infancy of oligosaccharide conjugate Haemophilus influenzae type
b vaccine in a United States Population: possible implications for optimal use.
J Infect Dis. 1992;165 (suppl 1):S139-S143.
24. Granoff DM, Anderson EL, Osterholm MT, et al. Differences in the immunogenicity
of three Haemophilus influenzae type b conjugate vaccines in infants.
J Pediatr. 1992;121:187-194.
25. Decker MD, Edwards KM, Bradley R, et al. Comparative trial in infants of
four conjugate Haemophilus influenzae type b vaccines. J Pediatr.
26. Adams WG, Deaver KA, Cochi SL, et al. Decline of childhood Haemophilus
influenzae type b (Hib) disease in the Hib vaccine era. JAMA. 1993;269:221-226.
27. Murphy TV, White KE, Pastor P, et al. Declining incidence of Haemophilus
influenzae type b disease since introduction of vaccination. JAMA.
28. Broadhurst LE, Erickson RL, Kelley PW. Decreases in invasive Haemophilus
influenzae diseases in US Army children, 1984 through 1991. JAMA.
29. Shapiro ED. Infections caused by Haemophilus influenzae type b:
the beginning of the end? JAMA. 1993;269:264-266.
30. Black SB, Shinefield HR, Lampert D, et al. Safety and immunogenicity of
oligosaccharide conjugate Haemophilus influenzae type b (HbOC) vaccine
in infancy. Pediatr Infect Dis J. 1991;10:92-96.
31. Black SB, Shinefield HR, Fireman B, et al. Efficacy in infancy of oligosaccharide
conjugate Haemophilus influenzae type b (HbOC) vaccine in a United States
Population of 61,080 children. Pediatr Infect Dis J. 1991;10:97-104.