Safety and immunogenicity of Haemophilus influenzae type B-Neisseria meningitidis group B outer membrane protein complex conjugate vaccine mixed in the syringe with diphtheria-tetanus-pertussis vaccine in young Gambian infants.

To ensure compliance and to reduce costs it is important, especially in less developed countries, that programs of child immunization should require as few clinic attendances and as few injections as possible. Therefore we have investigated whether a Haemophilus influenzae type b conjugate vaccine could be given safely and effectively with diphtheria-tetanus-pertussis vaccine (DTP). One hundred twenty-six Gambian infants were given both polyribosylribitol phosphate (PRP)-outer membrane protein complex (PedvaxHIB) and DTP on the same day at 8, 12 and 16 weeks of age; 60 were given the vaccines mixed in the syringe and 66 were given the vaccines separately. To minimize the injection volume the dose of PRP-OMPC used in both groups was 7.5 micrograms, which is half the usual dose. There were no significant differences in anti-PRP antibody titers between the groups after 1, 2 or 3 doses. The geometric mean titers of antibody for the two groups combined were 0.29 micrograms/ml 1 month after the first dose, 1.03 micrograms/ml after the second dose and 1.11 micrograms/ml after the third dose. Concentrations of antibodies to diphtheria, tetanus and pertussis 1 month after the third dose were not significantly different between the two groups. Systemic side effects were reported with equal frequency in the two groups and were similar to those reported elsewhere for DTP. Tenderness at the injection site was more common where the combined injection (0.75 ml) had been given than where DTP alone (0.5 ml) had been given. The main drawback to the use of these 2 vaccines together is the complexity of the mixing procedure used in this clinical trial.

Pneumococcal capsular polysaccharide-meningococcal outer membrane protein complex conjugate vaccines: immunogenicity and efficacy in experimental pneumococcal otitis media.

Vaccines composed of pneumococcal capsular polysaccharides (PS) conjugated to outer membrane protein complex (OMPC) from Neisseria meningitides group B bacteria were tested in the chinchilla otitis media model. Monovalent (types 6B and 23F), bivalent (6B+23F), and tetravalent (6B+14+19F+23F) PS-OMPC conjugate vaccines elicited significant total serum antibody responses against all four PS. Type 6B vaccine elicited IgG, IgM, and IgA antibodies after a single dose and an anamnestic IgG response after a second vaccine dose on day 28. Type 6B and 19F vaccines prevented or greatly attenuated pneumococcal otitis media after direct middle ear challenge with the immunizing serotype, type 14 vaccine was not protective by this challenge route, and type 23F pneumococci were not sufficiently virulent in chinchillas to test vaccine effectiveness. The promising results with two serotypes suggest the PS-OMPC conjugates may be useful in human infants.

Anti-PRP antibody levels after a primary series of PRP-OMPC and persistence of antibody titres following primary and booster doses.

The Haemophilus influenzae capsular polysaccharide-outer membrane protein conjugate, PRP-OMPC (PedvaxHIB) elicits very good antibody responses in infants > or = 2 months of age after the first dose. Increasing age at time of first vaccination correlates with higher antibody responses. Anti-PRP responses are consistently high with the first injection among all population groups studied. Booster doses stimulate anamnestic antibody responses after one year of age. Among US children (excluding Navajo and Apache children) given a primary injection at 14-18 months of age, the geometric mean titre (GMT) after 2 to 3 years was > 1 micrograms/ml. US children (excluding Navajo and Apache children) given a primary series at 2 and 4 months of age and a booster at 18 months of age also had an anti-PRP GMT > 1 micrograms/ml 2.5 years later. Navajo and Apache children given a primary series at 2 and 4 months of age and a booster at 12-15 months had antibody levels of 1.50 micrograms/ml one year later. Antibody persistence data suggest there will be long-term protection against Haemophilus influenzae b disease following immunization with PRP-OMPC.

Persistence of antibody at 18 months following vaccination of young Gambian infants with PRP-OMPC Haemophilus influenzae type b conjugate vaccine.

The rate of decline in anti-PRP antibody levels was measured in two groups of Gambian children who had been given PRP-OMPC at 1 and 3 months or 2 and 4 months of age. In the younger group (n = 70), the geometric mean titre fell from 1.32 micrograms/ml at 4 months to 0.44 micrograms/ml at 18 months. In the older group (n = 54), the geometric mean titre fell from 1.18 micrograms/ml at 5 months to 0.46 micrograms/ml at 18 months. The proportion of vaccinated children with antibody levels over 1.0 microgram/ml fell from 54% 1 month after the second dose of vaccine to 27% at the age of 18 months, while the proportion with levels over 0.15 micrograms/ml fell from 82% to 60%, with no significant differences observed between the vaccination groups. For those children who did not show evidence of environmental boosting, the half-life of anti-PRP antibody was about 100 days. This did not differ between the groups. These findings suggest that to provide lasting immunity PRP-OMPC should be given with a late booster dose at 12-15 months, as is the current practice in the USA. The need for a late booster dose may limit the value of this vaccine in developing countries where vaccination of children is difficult after the 1st year of life.

Immunogenicity of conjugate vaccines consisting of pneumococcal capsular polysaccharide types 6B, 14, 19F, and 23F and a meningococcal outer membrane protein complex.

In an effort to prepare pneumococcal (Pn) capsular polysaccharide (Ps) vaccines that would be immunogenic in infants, covalent conjugates were prepared for Pn types 6B, 14, 19F, and 23F. Each Ps type was covalently bound to an outer membrane protein complex from Neisseria meningitidis serogroup B and evaluated for immunogenicity in mice and infant monkeys. The conjugates induced specific anti-Ps antibody responses in mice and in infant rhesus and African green monkeys; a conjugate of 6B and outer membrane protein complex was immunogenic at Ps doses as low as 20 ng. Although low levels of the Pn group-common cell wall polysaccharide were present in all type-specific Ps preparations, anti-cell wall polysaccharide responses induced by covalent conjugates were < 1% of the total anti-Ps response after two doses of vaccine. In contrast, the anti-cell wall polysaccharide response of a noncovalent conjugate represented 41% of the anti-Ps response after two doses. Relative T-cell dependence, a requirement for the human target population of infants less than 18 months old, was demonstrated for all four Pn Ps conjugates in an athymic mouse model. Therefore, these Pn Ps-outer membrane protein complex conjugate vaccines are excellent candidates for evaluation in human infants.

Biological activity of Hib conjugates.

Haemophilus influenzae type b (Hib) conjugate vaccines dramatically improve the immunogenicity against the capsular polysaccharide (PRP) of Hib. A new Hib conjugate, PedvaxHIB, is shown to be immunogenic in infant rhesus monkeys. The monkey model appears to correlate well with the immunogenicity of PedvaxHIB in human clinical studies. Not all commercial Hib conjugates are immunogenic in the monkey model. The data from the priming study indicate that HibTITER is not immunogenic in an immune system naive to diphtheria toxoid, such as the infant rhesus monkey. The role of diphtheria toxoid in the immunogenicity of HibTITER in human infants should be studied.

Immunogenicity of Haemophilus influenzae type b conjugate vaccines in infant rhesus monkeys.

Two Haemophilus influenzae type b (Hib) polysaccharide-protein conjugate vaccines were evaluated for immunogenicity in eliciting anti-polyribosyl ribitol phosphate (PRP) antibodies in infant rhesus monkeys. Animals received intramuscular injections of either Hib polysaccharide (PRP)-meningococcal outer membrane protein complex or Hib oligosaccharide-CRM197 (HbOC) conjugate vaccines on d 0, 28, and 56. Because HbOC contains the CRM197 mutant diphtheria toxin from Corynebacterium diphtheriae as its protein carrier, the effect of simultaneous injection of diphtheria toxoid on the immunogenicity of HbOC also was evaluated by dividing monkeys vaccinated with HbOC into three groups: HbOC/saline, HbOC/diphtheria and tetanus toxoids, and HbOC/tetanus toxoid (coadministration of HbOC and other vaccine or placebo injected into the flank muscle of different legs). Infant monkeys vaccinated with the PRP-outer membrane protein complex conjugate responded with anti-PRP antibody after the first dose and showed booster responses after the second and third injections. In contrast, infant monkeys vaccinated with HbOC did not respond after three doses of HbOC/saline or HbOC/tetanus toxoid. However, two of three monkeys given concurrent injections of HbOC and diphtheria and tetanus toxoids did respond. The nonresponder monkey to three doses of HbOC and diphtheria and tetanus toxoids did respond to a subsequent injection with PRP-outer membrane protein complex. Thus, concomitant administration of diphtheria toxoid, a common vaccine for human infants, is necessary to elicit an anti-PRP antibody response to HbOC.(ABSTRACT TRUNCATED AT 250 WORDS)

An enzyme-linked immunosorbent assay for quantitation of Haemophilus Influenzae type b polysaccharide-specific IgG1 and IgG2 in human and infant rhesus monkey sera.

An enzyme-linked immunosorbent assay (ELISA) has been developed and validated to quantitate IgG1 and IgG2 antibody to polyribosyl-ribitol phosphate (PRP), the capsular polysaccharide of Haemophilus influenzae type b (Hib). The sera of children and infant Rhesus monkeys immunized with an Hib conjugate vaccine composed of Hib PRP covalently linked to an outer membrane protein complex (OMPC) from Neisseria meningitidis serogroup B (PedvaxHIB, PRP-OMPC, Merck, Sharp and Dohme Research Laboratories). The solid-phase antigen employed in the ELISA is a conjugate of PRP to human serum albumin. The enzyme-labeled antibody is alkaline phosphatase-conjugated mouse monoclonal (mAb) anti-human IgG1 or IgG2. A human serum standard was calibrated using parallel titrations with a known antibody standard. The geometric mean titer (GMT) of the anti-PRP IgG1 response to one dose of PedvaxHIB was 3.87 micrograms/ml (n = 82), 11.80 micrograms/ml (n = 62) and 14.57 micrograms/ml (n = 74) in infants and children 12 to 17 months, 18 to 23 months and greater than or equal to 24 months old, respectively. Infants 2 to 11 months old responded with an IgG1 anti-PRP response of 7.10 micrograms/ml while infant monkeys responded with a GMT of 150.65 (n = 9) after two doses of vaccine. The anti-PRP IgG2 GMT responses in all groups were less than 0.25 micrograms/ml, except for humans greater than or equal to 18-months old who exhibited a GMT of greater than or equal to 0.40 micrograms/ml (n = 75). PedvaxHIB, immunization of human infants and children and infant Rhesus monkeys elicits primarily an IgG1 response to PRP. The monkey model appears to be a reliable indicator of the human immune response.

Serologic responses to an Haemophilus influenzae type b polysaccharide-Neisseria meningitidis outer membrane protein conjugate vaccine in very young Gambian infants.

Recent studies in the United States and Europe have shown that Haemophilus influenzae type b polysaccharide-protein conjugate vaccines can induce protective antibody levels in young infants, but it was not clear that this would be the case in African infants, to whom H influenzae vaccines must be given at a very early age to prevent disease caused by H influenzae. Therefore, antibody responses to an H influenzae type b polysaccharide-Neisseria meningitidis outer membrane protein conjugate vaccine were measured in very young Gambian infants. In the first group (n = 85), to whom the vaccine was given at the ages of 1 and 3 months, the geometric mean antibody level rose from a prevaccination level of 0.23 microgram/mL to a postvaccination level of 1.27 micrograms/mL, and in the second group (n = 56), vaccinated at the ages of 2 and 4 months, the prevaccination level of 0.16 microgram/mL rose to a postvaccination level of 1.59 micrograms/mL. These two final postvaccination levels did not differ significantly, and interpolation suggests that similar antibody levels were present in both groups of infants at the age of 3 months. This is the age by which protection would need to be achieved to protect against H influenzae meningitis in The Gambia and in other countries where the infection has similar epidemiologic characteristics. No significant side effects of vaccination were noted.

Immunogenicity of a new Haemophilus influenzae type b conjugate vaccine (meningococcal protein conjugate) (PedvaxHIB).

Haemophilus influenzae type b is responsible for an estimated 15,000 to 20,000 cases of meningitis per year in the United States, mainly in children 2 months to 5 years old. The mortality rate from meningitis due to H influenzae type b infections ranges from 5% to 10%. Despite antibiotic treatment, up to 35% of survivors have permanent neurologic sequelae. In addition to meningitis, H. influenzae type b is responsible for other invasive infections, including epiglottitis, septicemia, cellulitis, septic arthritis, osteomyelitis, pneumonia, pericarditis, and otitis media; approximately 30,000 cases H influenzae diseases occur annually in the United States. The diseases peak in incidence between 6 and 12 months of age, with almost one half of the cases occurring before 1 year of age. About 75% of disease caused by H influenzae type b occurs in children younger than 24 months old. The incidence of disease is higher in children of certain groups, including blacks, Hispanics, Eskimos and Native Americans, young children attending day-care facilities, patients with asplenia or antibody-deficiency syndromes, and children of lower socioeconomic status. There is considerable evidence that antibody to the capsular polysaccharide (polyribosylribitol-phosphate [PRP] of H influenzae type b is protective.(ABSTRACT TRUNCATED AT 250 WORDS)

Haemophilus influenzae type b conjugate vaccine (meningococcal protein conjugate) (PedvaxHIB): clinical evaluation.

Although systemic infections caused by Haemophilus influenzae type b occur worldwide, detailed epidemiologic data are available in but a few countries. The public health impact of morbidity, mortality, and serious sequelae from disease caused by H influenzae type b has stimulated the search for control strategies. In the United States now, active immunoprophylaxis is largely favored over treatment of prophylaxis with antibiotics. This preference stems from three major observations: that high mortality and morbidity persist despite the availability of potent antimicrobial agents, that antibiotic-resistant strains of H influenzae type b have emerged, and that implementation of antimicrobial prophylaxis on a large scale has been unsatisfactory. Moreover, universal vaccination has been projected as offering a higher economic benefit than other control strategies. A matter of more proximate importance, however, is the search for H influenzae type b vaccines that will confer protection to all age groups, including infants younger than 18 months of age and subpopulations specifically at risk for invasive disease caused by H influenzae type b. Haemophilus b conjugate vaccine (meningococcal protein conjugate), PedvaxHIB (PRP-OMPC), is a conjugate H influenzae type b vaccine developed at Merck Sharp & Dohme Research Laboratories that now is undergoing extensive clinical evaluation to assess its prospects for disease control when first administered in early infancy. This is an interim report of results obtained in studies conducted in diverse locations throughout the United States.

Haemophilus influenzae type b polysaccharide-protein conjugate vaccine.

An Haemophilus influenzae type b capsular polysaccharide-protein conjugate has been prepared. The polysaccharide was coupled to the serotype II protein of group B meningococcus through the spacer 6-aminocaproic acid using cyanogen bromide and water soluble carbodiimide. The conjugate can be shown to be reproducible and is stable and highly immunogenic in mice and African green monkeys. Clinical evaluation of this conjugate in children 3 months to 4 years of age showed that it elicited an antibody titer to the polysaccharide moiety greater than 1000 ng/ml in children 8 months of age or older.

Streptococcus pneumoniae polysaccharide vaccine: age and dose responses, safety, persistence of antibody, revaccination, and simultaneous administration of pneumococcal and influenza vaccines.

Contemporary 14-valent pneumococcal polysaccharide vaccine was first licensed in 1977 in the United States, where about four million doses of vaccine have been distributed to date. The vaccine induces excellent antibody responses in elderly persons as well as in young adults. The antigen content of the vaccine is 50 microgram of each serotype of polysaccharide per dose, and lower titers of antibody are induced when the dose is reduced to 25 or 12.5 microgram of antigen. Adverse reactions are usually mild and consist principally of local erythema and induration at the injection site, with mild fever in a small proportion of subjects. Antibody persists well for at least four years, and it is expected that immunity will last for at least 5 years after vaccination. Local and systemic reactions to the vaccine may be greater when a second dose of vaccine is administered within three years after the initial dose, and this reactivity appears to be due to a Arthus-like response that results from local formation of antigen-antibody complexes. Pneumococcal and influenza vaccines can be injected simultaneously into separate sites without impairment of antibody responses to either vaccine; this feature should facilitate administration of these two vaccines.

Polyvalent pneumococcal polysaccharide vaccines.

A 14-valent pneumococcal vaccine has recently been licensed for general use after extensive testing in human subjects. Antibody production was satisfactory in 92% of individuals and a highly significant (76-92%) reduction was found in the rates for pneumococcal pneumonias caused by the capsular types present in the vaccine. Children over 2 years of age respond well to the vaccine, but younger children may not respond satisfactorily to some capsular types. In adults, the duration of the protective effect is at present unknown, but no substantial booster response was seen after a second dose at 1 year. Such a booster dose, in fact, induced a marked increase in the degree of local reaction at the injection site.