Immunogenicity study of Haemophilus influenzae type B conjugate vaccine in Indian infants

OBJECTIVE: To assess the immunogenicity in Indian infants to Haemophilus influenzae b oligosaccharide conjugate vaccine (HbOC). DESIGN: Prospective multicenter study. SETTING: Pediatric Out Patient Department of general hospitals in Pune and Mumbai. SUBJECTS: 124 full term healthy infants brought for routine DPT/OPV immunization. METHODS: Infants were administered 3 doses of 0.5 ml of HbOC, on the same day as their DPT/OPV immunization, injected intramuscularly on the limb opposite to that where DPT vaccine was administered. Data on local reactions and general symptoms was collected for three days after every dose. The children had their blood collected for assay of anti PRP (polyribosil ribitol phosphate) antibody titers, along with the first injection and one month after the third injection. One hundred and three infants completed the study protocol with two blood collections. RESULTS: The initial geometric mean titers (GMT) of 0.124 mcg/ml rose by 37 times to 4.552 mcg/ml. Ninety eight children (95.1%) had a final titer of > or = 0.15 mcg/ml, the minimum level associated with protection, and 77 children (74.8%) had a final level of > or = 1.0 mcg/ml, a level associated with long term protection. CONCLUSION: HbOC is immunogenic in Indian infants when used as per the locally recommended DPT/OPV immunization schedule.     

Antibody responses of three Haemophilus influenzae type b conjugate vaccines after one, two and three doses in Filipino children

Differences in the magnitude of antibody response after one, two or three doses of Haemophilus influenzae type b conjugate vaccines have been reported which may influence decision-making regarding which vaccine should be used. This is of particular importance in developing countries where children may not receive a full immunization series and the vaccination schedule may be delayed. Serum antibody responses to three Hib capsular polysaccharide protein conjugate vaccines (PRP-OMP, HbOC and PRP-T) were evaluated in 102 Filipino infants. Vaccination was carried out at 6, 10 and 14 weeks of age based on the national Expanded Programme on Immunization (EPI) schedule together with diphtheria-tetanus-pertussis, hepatitis B and oral poliomyelitis vaccines. Sera were collected at 6 weeks and 1 month after each vaccination. Anti-Hib polysaccharide antibody concentrations were determined by Farrtype radioimmunoassay (RIA) and enzymeimmunoassay (EIA), Following the first dose, the geometric mean concentrations (GMC, micrograms ml-1) for PRP-OMP, HbOC and PRP-T were 0.69, 0.27 and 0.38, respectively. After two doses, there was a significant response (P < 0.05) to PRP-OMP and PRP-T (0.89 and 1.47) but not for HbOC (0.37). Differences in the GMC after the primary series were significant (pairwise P < 0.05): GMC was highest for PRP-T (4.0), followed by HbOC (1.6) and PRP-OMP (1.1). All three Hib vaccines were immunogenic when given in the local EPI schedule in Filipino infants although significant differences in the kinetics and magnitude of antibody responses were noted. The anti-Hib antibody concentrations determined by RIA and EIA were also compared in order to validate the latter for use in laboratories where it is feasible. There was a good correlation (r2 = 76%; P = 0.0001) in the Hib antibody titres obtained by both assays.     

Molecular size characterization of Haemophilus influenzae type b polysaccharide-protein conjugate vaccines

Current vaccines against Haemophilus influenzae type b (Hib) consist of capsular polysaccharide, polyribosylribitol phosphate (PRP), chemically conjugated to a carrier protein. The stability of the conjugate is essential for vaccine efficacy, as the target population for this vaccine includes infants, who do not mount an immune response to free polysaccharide vaccines. A method has been developed for determining structural stability and batch-to-batch consistency of Hib vaccines by the application of fast protein liquid chromatography (FPLC). This FPLC method is fast, reproducible, and can be used to evaluate single human doses of Hib vaccines. We have shown that the FPLC elution profiles provide a suitable indicator of vaccine stability under normal and degradative conditions. The method may also be applicable to other conjugate vaccines such as meningococcal and pneumococcal protein-polysaccharide conjugates.     

Interchangeability of Haemophilus influenzae type b vaccines in the primary series: evaluation of a two-dose mixed regimen

OBJECTIVE: To evaluate two- or three-dose "mixed" regimens of Haemophilus influenzae type b conjugate vaccines in the priming series. DESIGN: Two randomized clinical trials with 140 and 181 infants, respectively. SETTING: Private practices in New Orleans and Chicago. METHODS: In trial I, infants received one of four regimens. Two were recommended regimens for polyribosylribitol phosphate (PRP)-meningococcal protein conjugate (M) and PRP-tetanus toxoid conjugate (T). Two mixed regimens consisted of M at 2 months followed by two doses of T or PRP-diphtheria toxoid conjugate (D) at 4 and 6 months. Trial II consisted of three groups. Two were recommended regimens for M and T. The third was a two-dose mixed regimen consisting of M at 2 months and T at 4 months. Parents were interviewed and instructed to record side effects after each vaccination. Serum was assayed for H influenzae type b anticapsular antibody (anti-PRP). RESULTS: Minor differences in safety profiles likely reflected alpha error. In trial I, M (lot 0884T, one of several known to have had decreased immunogenicity), probably primed for substantial increase in serum antibody when D or T was given at 4 and 6 months. In trial II, infants who received the two-dose mixed regimen (M from immunogenic lot 0116W at 2 months and T at 4 months) had a significantly higher mean area under the curve than recipients of the three-dose TTT regimen when antibody concentration was plotted against age, although the geometric mean anti-PRP antibody concentration for the MT-recipients was significantly lower at 7 months. CONCLUSIONS: M used in trial I may have primed infants despite poor immunogenicity. The two-dose mixed regimen (MT-) in trial II produced a mean anti-PRP antibody concentration with higher sustained anti-PRP concentrations from 2 to 7 months, as judged by the area under the curve, but a lower mean anti-PRP antibody concentration at 7 months.     

Haemophilus influenzae type b-specific antibody in infants after maternal immunization

OBJECTIVE: To study the kinetics of Haemophilus influenzae type b (Hib)-specific antibody in infants born to mothers immunized with an Hib polysaccharide or one of two Hib conjugate vaccines. STUDY DESIGN: Serum antibody to the polyribosylribitol (PRP) moiety of Hib was measured by radioimmunoassay and enzyme-linked immunosorbent assay at birth and at 2 and 6 months of age in infants born to women immunized with Hib polysaccharide or conjugate vaccine (PRP-D and HbOC). A subset of infants > or = 6 months of age was immunized with Hib conjugate vaccine after licensure of this vaccine for infants. A comparison group of 18 infants born to unimmunized women received the same Hib conjugate vaccine on a similar schedule. RESULTS: Total PRP antibody concentrations were 1.50, 14.4 and 20.4 microg/ml in 2-month-old infants born to mothers immunized with polysaccharide, PRP-D and HbOC vaccines, respectively, and 2.54, 1.35 and 2.46 microg/ml in 6-month-old infants. Infants born to mothers immunized with polysaccharide vaccine had significantly less PRP antibody at 2 months of age but similar antibody concentrations at 6 months of age. Persistence or increases in total PRP antibody during 6 months were noted in 21 of 47 (44.6%) study infants. A subset of study and comparison infants was immunized with a mean of 2.6 doses of Hib vaccines between 6 months and 2 years of age, and all infants had total PRP antibody concentrations > or = 0.15 microg/ml. CONCLUSION: Conjugate Hib vaccines administered during the last trimester of pregnancy resulted in significantly higher PRP antibody titers in infants at birth and 2 months of age than did polysaccharide vaccine. A subset of infants born to immunized mothers was subsequently immunized with Hib conjugate vaccine and had antibody concentrations similar to those in infants born to nonimmunized women.     

The use of Haemophilus influenzae type b-tetanus toxoid conjugate vaccine mixed with diphtheria-tetanus-pertussis vaccine in Gambian infants

In preparation for an efficacy trial of PRP-T Haemophilus influenzae type b conjugate vaccine, 251 Gambian infants were randomized to receive three doses of PRP-T and diphtheria-tetanus-pertussis (DTP) vaccines at 2, 3 and 4 months of age, either by separate injections, or combined in the same syringe. One month after the third dose, there was no difference between anti-PRP levels in those infants who received the vaccines separately (GMT 5.83 micrograms ml-1), and those who received the vaccines combined (GMT 5.57 micrograms ml-1). The proportions achieving levels of 1.0 microgram ml-1 were 89% and 92% in the "separate" and "combined" vaccine groups, respectively. There were no significant differences between groups in levels of antibody to diphtheria or tetanus. Geometric mean titres of antibody directed against pertussis antigens in the "separate" and "combined" groups were as follows: pertussis toxin 14.2 and 13.1 ELISA units (EU) ml-1; filamentous haemagglutinin 12.2 and 9.7 EU ml-1; pertactin 17.2 and 9.0 EU ml-1 (P < 0.05), fimbrial 2/3 antigens 449 and 364 EU ml-1. The combination of PRP-T and DTP in the syringe prior to administration is safe and immunogenic. The lower levels of anti-pertussis antibody are of unknown clinical significance.     

Enhanced antibody response in Venezuelan infants immunized with Haemophilus influenzae type b-tetanus toxoid conjugate vaccine

The safety and immunogenicity of primary immunization at 2, 4 and 6 months of age with Haemophilus influenzae type b capsular polysaccharide conjugated to tetanus toxoid (PRP-T; Act-HIB) were evaluated in infants in Valencia, Venezuela. In order better to assess reactions to PRP-T, subjects received their initial PRP-T vaccine a mean of 6.5 days after their initial diphtheria-tetanus-pertussis (DTP) vaccine. The PRP-T vaccine was well tolerated. Serum was obtained at ages 2 and 7 months (before the first and 1 month after the third PRP-T dose). Antibody responses were compared with those from Nashville infants who had received PRP-T and DTP simultaneously in a previous trial. The preimmunization titers in the Venezuelan and Nashville infants did not differ. The geometric mean postimmunization titer in the Venezuelan infants was 37.9 micrograms/ml, as compared with 3.63 micrograms/ml in the Nashville infants (P < 0.00001). Possible explanations for the exceptional antibody response of these Venezuelan infants to PRP-T include carrier priming caused by prior DTP immunization, synergy associated with the specific DTP vaccine used, preimmunization immunologic experience that differed from their United States counterparts and genetic differences that altered response to the vaccines. Further studies are proposed to evaluate these possibilities.     

A routine high-performance size-exclusion chromatography to determine molecular size distribution of Haemophilus influenzae type b conjugate vaccines

High-performance size exclusion chromatography has been used to determine the molecular size distribution of Haemophilus influenzae type b (Hib) conjugate vaccines. Both high molecular weight preparations of native Hib capsular polysaccharide coupled to tetanus toxoid and low molecular weight vaccines with Hib oligosaccharides linked to the CRM197 nontoxic mutant diphtheria protein were analysed. Columns with different fractionation ranges were used for the two kinds of vaccines. This method showed to be rapid, accurate and reproducible for different lots of Hib vaccine of different composition produced by various manufacturers. It could replace more time-consuming chromatographic methods enabling control authorities to employ a single methodological approach for different Hib vaccines.     

Conjugate vaccines and the carriage of Haemophilus influenzae type b

Pharyngeal carriage of Haemophilus influenzae type b (Hib) is important in the transmission of Hib organisms, the pathogenesis of Hib disease, and the development of immunity to the bacterium. The remarkable success of current vaccination programs against Hib has been due in part to the effect of conjugate Hib vaccines in decreasing carriage of Hib. This review explores evidence for this effect, and discusses the possible mechanisms of the mucosal influence of Hib conjugate vaccines.     

Invasive infection with Haemophilus influenzae type b in spite of complete vaccination

Five patients, 4 boys and 1 girl aged 13-41 months, developed invasive Haemophilus influenzae type b (Hib) disease (2 epiglottitis, 3 meningitis) despite full (or at least 3 times) vaccination. At admission as well during convalescence, 3 out of 5 had IgG anti Hib antibody levels < or = 5 U/ml. Serum immunoglobulin levels, including IgG subclasses, as well as complement were normal in all cases. In 2 of the 3, booster vaccinations with Hib conjugate vaccine elicited adequate antibody titres. Since the incorporation of the conjugated Hib polysaccharide tetanus toxoid vaccine (HibTT) in the National Vaccination Programme in the Netherlands, the number of invasive infections caused by Hib has dropped significantly. Causes of Hib conjugate vaccine failures are mostly unknown. In about one-third of the cases serum immunoglobulin levels are deficient, most often IgG2 or IgM. Susceptibility to Hib infection is in part also genetically determined. In the follow-up of Hib vaccine failures, anti Hib antibody titres should be determined. Booster vaccinations may be necessary.     

Preclinical studies on a recombinant group B meningococcal porin as a carrier for a novel Haemophilus influenzae type b conjugate vaccine

In anticipation of future combination vaccines, a recombinant class 3 porin (rPorB) of group B meningococci was evaluated as an alternative carrier protein for a Haemophilus influenzae type b (Hib) polyribosylribotol phosphate (PRP) conjugate vaccine. The use of rPorB may avoid undesirable immunologic interactions among vaccine components, including epitopic suppression from conventional carriers (e.g. tetanus toxoid [TT]), as well as provide desirable immunomodulatory effects. Rats were found to be more reliable and consistent than mice or guinea pigs for studying antibody responses to the Hib conjugates. Different Hib conjugates, Hib-TT and Hib-rPorB, consisting of PRP conjugated by reductive amination to TT or rPorB, were compared in rats. Commercially available, licensed vaccines, HbOC (HibTITER) and PRP-T (OmniHib), were used as reference controls. Maximum geometric mean ELISA IgG titers were obtained in rats after only two doses, showing booster effects for all. However, Hib-rPorB immunization consistently resulted in responses that were 1-2 orders of magnitude greater than those for the other conjugates, including the licensed control vaccines. A maximum 4600-fold rise was observed for Hib-rPorB after two doses, and, unlike the other conjugates, a 100% response rate was always achieved without adjuvant. These results warrant further investigation of Hib-rPorB in combination with DTaP.     

Antibody responses to tetanus toxoid and Haemophilus influenzae type b conjugate vaccines following autologous peripheral blood stem cell transplantation (PBSCT)

OBJECTIVE: Although there are many anecdotal reports that psychological intervention is effective in enhancing adjustment to spinal cord injury (SCI), there are little data to support this assertion. To date, reports of few longitudinal-based controlled trials that assessed psychological outcomes for SCI persons have been published. This study was conducted to determine long-term efficacy of cognitive behavior therapy during rehabilitation. DESIGN: The study employed a nonrandomized controlled trial, and measures were taken on three occasions: before, immediately after, and 12 months after treatment. SETTING, OUTCOME MEASURES, AND INTERVENTION: Anxiety, depressive mood, and self-esteem were assessed in 28 SCI persons consecutively selected on admission to hospital, who participated in specialized group cognitive behavior therapy (CBT) during rehabilitation. CONTROLS: The intervention group's responses on the measures were compared with a control group of 41 SCI persons who only received traditional rehabilitation services during their hospitalization. RESULTS: There were no overall group differences on anxiety, depressive mood, and self-esteem, although there was a trend for the treatment group to have greater levels of improvement in depression scores across time in comparison to the control group. However, those in the treatment group who reported high levels of depressive mood before the CBT treatment were significantly less depressed 1 year after injury, compared to similar persons in the control group. CONCLUSIONS: While it appears not everyone who experiences SCI needs CBT, at least in the hospital phase of their rehabilitation, those who report high levels of depressive mood benefited greatly from CBT.     

Opposite effects of actively and passively acquired immunity to the carrier on responses of human infants to a Haemophilus influenzae type b conjugate vaccine

Recent advances in the molecular modelling of carbohydrates have brought this technique to a level comparable with that of protein and nucleic acid simulations. After a brief introduction to the techniques used in the computer simulation of carbohydrates and carbohydrate interactions, an overview of applications in the field of carbohydrate-related drug discovery is presented.     

CD1 presents antigens from a gram-negative bacterium, Haemophilus influenzae type B

Human CD1 is a family of nonpolymorphic major histocompatibility complex class I-like molecules capable of presenting mycobacterial lipids, including lipoarabinomannan (LAM), to double-negative (DN; CD4(-) CD8(-)) as well as CD8(+) T cells. Structural similarities between LAM and the capsular polysaccharides of gram-negative bacteria led us to consider the latter as candidate CD1 ligands. We derived two CD1-restricted DN T-cell populations which proliferated to Haemophilus influenzae type b (Hib) antigen. One T-cell population also proliferated to proteinase K-treated Hib antigen, suggesting that it recognized a nonpeptide. Our work thus expands the universe of T cell antigens to include nonpeptides distinct from mycobacterial lipids and suggests a potential role for CD1-restricted T cells in immunity to Hib.     

Epidemiology of invasive Hemophilus influenzae B infections in Bedouins and Jews; conjugate Hib vaccines

From 1989 to 1996, 139 cases of invasive Hemophilus influenzae B (Hib) infections were identified in children in the Negev, 110 of which occurred before introduction of the conjugate vaccine (1989-92). At that time there were 60.5 cases of Hib per 100,000 in the Negev among children under 5 years of age. During 1995-1996, when Hib conjugate vaccine was part of the regular immunization program, Hib decreased to 6.5 cases per 100,000 in that age group. The effectiveness of PRP-OMP vaccine was 96.5% among Jews and 89% among Bedouins, and the efficacy of the immunization program was 99.99%. This degree of success exceeded all expectations based on the literature. During the whole study period, Hib infections were more frequent among Bedouins than Jews. There was no significant difference in the occurrence of Hib among Jews in the Negev before and after the vaccine was introduced. Hib among Bedouins in the Negev was significantly more frequent than in the Israeli population as a whole before the vaccine was introduced. That gap narrowed after the vaccine was introduced because of the decrease in morbidity among the 2 groups.     

Clinical acceptability and immunogenicity of a pentavalent parenteral combination vaccine containing diphtheria, tetanus, acellular pertussis, inactivated poliomyelitis and Haemophilus influenzae type b conjugate antigens in two-, four- and six-month-old Chilean infants

The syndromes of Sotos and Weaver are paradigmatic of the daily nosologic difficulties faced by clinical geneticists attempting to diagnose and counsel, and to give accurate prognoses in cases of extensive phenotypic overlap between molecularly undefined entities. Vertebrate development is constrained into only very few final or common developmental paths; therefore, no developmental anomaly seen in humans is unique to ("pathognomonic" of) one syndrome. Thus, it is not surprising that prenatal overgrowth occurs in several syndromes, including the Sotos and Weaver syndromes. Are they sufficiently different in other respects to allow the postulation of locus (rather than allele) heterogeneity? Phenotypic data in both conditions are biased because of ascertainment of propositi, and the apparent differences between them may be entirely artificial as they were between the G and BBB syndromes. On the other hand, the Sotos syndrome may be a cancer syndrome, the Weaver syndrome not (though a neuroblastoma was reported in the latter); in the former there is also remarkably advanced dental maturation rarely commented on in the latter. In Weaver syndrome there are more conspicuous contractures and a facial appearance that experts find convincingly different from that of Sotos individuals. Nevertheless, the hypothesis of locus heterogeneity is testable; at the moment we are inclined to favor the hypothesis of allele heterogeneity. An international effort is required to map, isolate, and sequence the causal gene or genes.     

The decline of Haemophilus influenzae type b disease in Australia

Between July 1993 and June 1996, there were 412 cases of invasive Haemophilus influenzae type b (Hib) disease reported to the Hib Case Surveillance Scheme, 71% in children under the age of five years. Meningitis was the most frequent illness reported, followed by epiglottitis, septicaemia and pneumonia. There were 18 deaths. Thirty-four cases were classified as vaccine failures. The number of vaccine failures increased over time and the total number of cases of Hib disease fell, consistent with an increase in Hib vaccine coverage. Based on an estimated vaccine coverage of 50% in April 1995, the vaccine efficacy for all vaccines in the period was estimated to be 89%. Invasive Hib is a serious illness of childhood which is being significantly reduced by the use of Hib vaccines, and has the potential to be eliminated from this country. Vaccination providers should aim to immunise all children against Hib disease on time and according to the National Health and Medical Research Council Standard Vaccination Schedule.     

Subdural effusion in type B Haemophilus influenzae meningitis. A study of 38 cases

OBJECTIVE: Studying clinical, laboratory and radiologic findings, as well as outcome, observed in patients with meningitis caused by Hib, and its relationship with subdural effusion. MATERIAL AND METHODS: Retrospective study of 38 meningitis caused by Hib. Patients were aged between 3 months and 5 years. Imaging was performed in 26 cases (68%): CT in 21 children (55%) and cranial sonography in 11 cases (29%). EEG was made in 29 patients (76%) and auditory-evoked potentials in 13 (34%). The mean follow-up period after discharge was 24 months. RESULTS: Sixty-six per cent were male and 34% female. Eight cases had subdural effusion. These patients showed higher white cell counts in blood and CSF, higher levels of proteins in CSF, and lower levels of glucose in the same medium. They also had seizures before or during hospitalization, with higher frequency than those without subdural effusion (50% vs 26%) as well as more prolonged fever (127 vs 73 hours). No specific treatment was required in any case. CONCLUSIONS: Subdural effusion is one of the most frequent complications observed in meningitis. Patients frequently present more important clinical and laboratory alterations. This finding is not related with neurologic sequelae and they resolve spontaneously with time.     

Assessment of the immunogenicity and reactogenicity of a quadrivalent diphtheria, tetanus, acellular pertussis and hepatitis B (DTPa-HBV) vaccine administered in a single injection with Haemophilus influenzae type b conjugate vaccine, to infants at 2, 4 and 6 months of age

This double-blind, randomised study was performed to assess the immunogenicity and reactogenicity of three lots of a quadrivalent diphtheria-tetanus-acellular pertussis-hepatitis B vaccine (DTPa-HBV) co-administered with three lots of Haemophilus influenzae type b conjugate (Hib) vaccine in one injection, as a primary vaccination course in healthy infants at 2, 4 and 6 months of age. 269 infants (8-11 weeks of age) were randomly allocated to three groups to receive DTPa-HBV/Hib vaccines, concomitantly with oral polio vaccine. Blood samples for antibody determinations were taken before vaccination and 1 month after the third dose in 262 subjects. Local and general symptoms were recorded by parents on diary cards. All vaccinees had post-vaccination protective anti-D and anti-T (> or = 0.1 IU ml-1) antibodies, and 98% had protective anti-HBs antibody titres (> or = 10 mIU ml-1). There were no statistically significant differences between groups in post-vaccination anti-D, anti-T, anti-HBs antibody geometric mean titres (GMT), these being 3.49 IU ml-1, 5.92 IU ml-1 and 1109 mIU ml-1, respectively. All subjects responded to three pertussis components, i.e. pertussis toxin (PT), filamentous haemagglutinin (FHA) and pertactin (PRN). Although statistically significant differences in GMTs of anti-PT, anti-FHA and anti-PRN were found between groups, these were not believed to be of any clinical relevance as the minimum GMTs were 60, 193 and 230 EL.U ml-1 for anti-PT, anti-FHA and anti-PRN, respectively. There were no statistically significant differences in anti-PRP antibody GMT (4.05 micrograms ml-1) between groups, 100% and 85% of subjects having titres > or = 0.15 and 1.0 microgram ml-1, respectively. No symptoms were reported for one third of the subjects. Fever (> 38 degrees C) was reported after 16% of doses, with < 1% having > 39.5 degrees C. Almost all local and general symptoms were mild or moderate, and lasted less than 48 h. No subject dropped out due to a severe adverse reaction. The administration of an experimental mix of DTPa-HBV and Hib vaccines in a single injection is safe, well-tolerated and immunogenic for all vaccine components.