Comparison of five different vaccination schedules with Haemophilus influenzae type b-tetanus toxoid conjugate vaccine

Protein carriers of conjugate vaccines: characteristics, development, and clinical trials

The immunogenicity of polysaccharides as human vaccines was enhanced by coupling to protein carriers. Conjugation transformed the T cell-independent polysaccharide vaccines of the past to T cell-dependent antigenic vaccines that were much more immunogenic and launched a renaissance in vaccinology. This review discusses the conjugate vaccines for prevention of infections caused by Hemophilus influenzae type b, Streptococcus pneumoniae, and Neisseria meningitidis. Specifically, the characteristics of the proteins used in the construction of the vaccines including CRM, tetanus toxoid, diphtheria toxoid, Neisseria meningitidis outer membrane complex, and Hemophilus influenzae protein D are discussed. The studies that established differences among and key features of conjugate vaccines including immunologic memory induction, reduction of nasopharyngeal colonization and herd immunity, and antibody avidity and avidity maturation are presented. Studies of dose, schedule, response to boosters, of single protein carriers with single and multiple polysaccharides, of multiple protein carriers with multiple polysaccharides and conjugate vaccines administered concurrently with other vaccines are discussed along with undesirable consequences of conjugate vaccines. The clear benefits of conjugate vaccines in improving the protective responses of the immature immune systems of young infants and the senescent immune systems of the elderly have been made clear and opened the way to development of additional vaccines using this technology for future vaccine products.

Immunogenicity of Haemophilus influenzae type b conjugate vaccines in Korean infants: a meta-analysis

A meta-analysis was performed on the immunogenicity of Haemophilus influenzae type b (Hib) conjugate vaccines after 2 (2 and 4 months) and 3 doses (2, 4, and 6 months) in Korean infants. A database search of MEDLINE, KoreaMed, and Korean Medical Database was done. The primary outcome measure was the proportion of infants with anti-polyribosylribitol phosphate (PRP) concentrations > or =1.0 microg/mL. Eight studies including eleven trials were retrieved. One trial reported on the diphtheria toxoid conjugate vaccine (PRP-D) and 2 trials each on the mutant diphtheria toxin (PRP-CRM) and Neisseria meningitidis outer-membrane protein (PRP-OMP) conjugate vaccine. Heterogeneity in study designs between trials on PRP-CRM was noted and one trial reported on a monovalent and another on a combination PRP-OMP vaccine. Thus, a meta-analysis was conducted only on the tetanus toxoid conjugate vaccine (PRP-T). After a primary series of 2 doses and 3 doses, 80.6% (95% confidence interval [CI]; 76.0-85.1%) and 95.7% (95% CI; 94.0-98.0%) of infants achieved an antibody level > or =1.0 microg/mL, respectively. The immunogenic response to the PRP-T vaccine was acceptable after a primary series of 3 doses and also 2 doses. A reduced number of doses as a primary series could be carefully considered in Korean infants.

Ventrogluteal area—a suitable site for intramuscular vaccination of infants and toddlers

Buttock vaccination has lower reactogenicity and similar immunogenicity to the two other recommended paediatric vaccination sites (deltoid and anterolateral thigh). Safety concerns about buttock injection derived from injections with neurotoxic agents, like penicillin but not vaccines, have become entrenched. However, the ventrogluteal area is considered safe for intramuscular injection. This study outlines the development of the ventrogluteal area as a suitable site for intramuscular vaccination of infants and toddlers. Measurement was made in 642 children, aged 2-18 months and age-specific templates were prepared. These were used in an untrasonographic study of 57 children aged 2-18 months to determine the tissue composition of the ventrogluteal area compared with the recommended anterolateral thigh vaccination site. The ventrogluteal area was found to be clearly defined by the template and suitable for intramuscular injection. Subsequent vaccination studies with the area showed that it was:

Humoral immune responses to a protective peptide-conjugate against measles after different prime-boost regimens

The current live-attenuated measles vaccine leaves many children unprotected until they reach the recommended age of vaccination. We have previously shown that the short peptide corresponding to the hemagglutinin noose epitope (HNE) of the measles virus (MV) hemagglutinin protein induced virus-neutralizing antibodies even in the presence of protective levels of anti-whole virus-specific antibodies. Here we investigate the immunogenicity of HNE peptide-conjugates of diphtheria or tetanus toxoid in mice after active and passive priming with antibodies against the peptide, toxoids and conjugates. Both conjugates induced high titers of peptide antibodies which crossreacted with the virus and protected against a lethal intracranial challenge with a rodent-adapted measles virus, even after active priming with homologous or heterologous toxoid or conjugate. Peptide-specific epitopic suppression was stronger after passive priming with carrier or conjugate antibodies, but diphtheria toxoid as a carrier was less susceptible to suppression than tetanus toxoid and suppression was overcome by an additional boost. Furthermore, prior immunization with peptide-conjugate did not interfere with the development of a complete response to a subsequent injection of MV, suggesting that the benefits of a follow-up vaccination with the current live-attenuated vaccine would not be lost. These results underline the potential of these peptide-based conjugates as vaccine candidates for use in early infancy to close the window of susceptibility before the live-attenuated vaccine can be administered.

Greater antibody responses to an eleven valent mixed carrier diphtheria- or tetanus-conjugated pneumococcal vaccine in Filipino than in Finnish or Israeli infants

BACKGROUND

Antibody responses to pneumococcal conjugate vaccines may vary when administered in different populations or epidemiologic settings. Understanding the causes and significance of this variation could help to determine the number of doses and timing required for protection against pneumococcal diseases in each country.

METHODS

This report compares antibody responses to aluminum-adjuvanted and nonadjuvanted mixed carrier 11-valent diphtheria- or tetanus-conjugated pneumococcal vaccine (11-PncTD) formulations when given at 6, 10 and 14 weeks and 9 months of age to Filipino infants (n = 51) and at 2, 4, 6 and 12 months of age to Finnish (n = 127) and Israeli (n = 124) infants. The study populations differ in their natural exposure to pneumococcus and risk factors for pneumococcal carriage and disease.

RESULTS

Filipino and Israeli infants had slightly but significantly higher prevaccination geometric mean concentration (GMC) of antibodies than did the Finnish infants. After three doses of aluminum-adjuvanted 11-PncTD vaccine, the Filipino infants had 1.8 to 6.7 and 1.5 to 5.0 times higher GMC than the Finnish and Israeli infants, respectively, against pneumococcal serotypes conjugated to tetanus protein. The GMC of serotypes conjugated to diphtheria toxoid was 1.3 to 3.0 and 0.7 to 2.0 times the GMC in Finnish and Israeli infants, respectively. The nonadjuvanted vaccine formulation induced generally lower GMCs.

CONCLUSIONS

The antibody responses to the tetanus-conjugated polysaccharides were considerably higher in the Filipino than in the Finnish or Israeli infants. This may be a result of several factors including the priming effect of tetanus toxoid given to pregnant women, early pneumococcal nasopharyngeal acquisition and genetic differences among populations.

Antibody response to Haemophilus influenzae type b tetanus conjugate vaccine with two doses given at 3 and 5 months of age

BACKGROUND

In developed countries, the use of Hib conjugate vaccines has led to the near disappearance of invasive Hib disease, but costs have limited its use in developing countries. In order to identify more economical vaccination schedules, we carried out a trial to evaluate the immunogenicity of an alternative two-dose PRP-T regimen, based on a previous report in which carrier priming could be obtained with prior diphtheria-tetanus-pertussis (DTP) vaccination.

METHODS

Healthy infants were enrolled to receive the PRP-T given at 3 and 5 months of age, with DTP vaccination given at 2, 4 and 6 months of age. Serum specimens were obtained at 3, 6 and 15 months of age. IgG anti-Hib titer determination was performed using enzyme-linked immunosorbent assay to evaluate serologic response and its duration.

RESULTS

One-hundred and seventeen infants were enrolled. The geometric mean titer (GMT) of antibody to PRP was low in the pre-immunization samples (0.13 mg/mL), achieving high values after two doses of PRP-T (27.42 mg/mL), with all titers over 1 mg/mL; the GMT at 15 months was 5.45 mg/mL; 94.6% of infants had serologic responses after the two doses of vaccination, with average intervals of 27 and 22 days between DTP and PRP-T first-to-first and second-to-second administrations, respectively. However, these intervals were 11 and 3 days for infants who did not have serologic responses (P50.0013 and 0.0030, respectively).

CONCLUSIONS

These results indicate that two doses of PRP-T can induce high antibody titers using the proposed schedule; moreover, the GMT assessed at 15 months of age was also protective. The enhanced immune response observed in the study could be explained by the previous administration of the DTP vaccine, since the longer the interval between DTP and PRP-T, the better the response to Hib vaccine. The PRP-T vaccine given at 3 and 5 months of age may be an economical alternative to the current proposed schedule, which could make the introduction of Hib vaccination in developing countries more feasible, considering the relatively high cost of this vaccine.

Age- and dose-interval-dependent antibody responses to inactivated poliovirus vaccine

Antibody responses were studied in five groups of children immunized with different three-dose schedules of inactivated poliovirus vaccine (IPV). The age of the child at the first dose (1-4 months) and the interval between the first and second doses (2-4 months) influenced the initial responses in a serotype-dependent manner. All the groups attained sufficient antibody level after three doses but the third dose given at 18 months resulted in higher persisting antibody levels than that given at 12 months. The highest persisting antibody titers against PV1 and PV2 (but not against PV3) at the age of 3 years were measured in the control group immunized with the current schedule (P < 0.001) in which the first dose is given at 6 months. The level of maternal antibodies present at the time of the first dose correlated negatively with the antibody titers as late as at 3 years of age. It is concluded that three doses of IPV given in widely variable schedules may result in satisfactory immune responses in children but, for optimal results, very early onset of the program and short dosage intervals should be avoided.

Inactivated poliovirus vaccine and the final stages of poliovirus eradication

The use of the inactivated poliovirus vaccine (IPV) will increase before and probably also after the global eradication of the wild type poliovirus. Before eradication, the switch from the use of oral poliovirus vaccine (OPV) to IPV has been due to the better safety record of IPV. Introduction of IPV in the regular immunisation schedules is made easier by the development of several combination vaccines, including IPV. Maternal antibodies and young age, often considered problematic for early initiation of IPV schedules, did not compromise optimal maintenance of seropositivity during infancy or long-term persisting antibody levels in our studies. OPV-derived, potentially pathogenic and transmissible poliovirus strains, excreted by some individuals for years, may present a problem for a blunt stopping of all polio immunisations after eradication. Our recent results suggest that locally excreted IgA might have a role in the elimination of poliovirus infection in the intestinal tissues.

Prospects for pneumococcal vaccination in African children

Streptococcus pneumoniae (pneumococcus) remains a major cause of morbidity and mortality in both developed and undeveloped countries. Accurate disease burden estimates for developing countries and Africa in particular, where diagnostic facilities are less adequate and a disease surveillance system virtually non-existent, is difficult. However, from conservative estimates, the pneumococcus is probably responsible for at least 1 million of the 4 million deaths that occur from acute lower respiratory infections in children aged less than 5 years. The global burden of disease has been accentuated by the rising menace of multi-drug resistant strains, which defy geographic and racial borders. Thus, now more than ever before, there is an urgent need to identify and implement preventive measures to avert this problem. The currently licensed pneumococcal polysaccharide vaccine, comprises 23 capsular polysaccharides of the pneumococcus, many of which are poorly immunogenic in the very vulnerable age group of under-fives. A possible solution to the problem of poor immunogenicity is to use a protein/polysaccharide conjugate vaccine similar to that recently introduced successfully for Haemophilus influenzae type b (Hib) and using this approach, several workers have reported promising results from safety and immunogenicity studies. However, unlike Hib, the development of conjugate vaccine against pneumococcal disease is complicated by the existence of more serotypes than can be feasibly incorporated in a single conjugate vaccine formulation. Whilst this challenge has been taken on by some vaccine manufacturers, novel approaches such as the identification or construction of protective protein antigen, common to all clinically important strains are being explored. Novel application of the pneumococcal polysaccharide vaccines in pregnancy for protection of disease in early infancy is an approach that has not been evaluated. For maximum impact, the ultimate vaccine formulation should be affordable and available to resource poor countries where the burden of disease is highest. Establishing disease surveillance systems in such countries now will greatly facilitate the introduction of the vaccines.

A comparative study of PENTA vaccine booster doses given at 12, 15, or 18 months of age

For infants immunized with Haemophilus influenzae type b conjugate vaccines, booster immunization is usually recommended in the second year of life, typically between 12 and 18 months. This study assessed the effect of age at booster immunization on pre-immunization antibody trough levels and on subsequent responses, for a PRP-T conjugate vaccine. Subjects were healthy children who had received PENTA vaccine (DPT-IPV/PRP-T combination) as infants. They were enrolled and given measles-mumps-rubella vaccine (MMR) at 12 months of age, then randomly assigned to receive PENTA vaccine concurrently with MMR or at 15 or 18 months of age. Parents were asked to note any adverse effects after PENTA vaccination. Blood samples were obtained prior to PENTA vaccination and 4 weeks later, and tested for antibodies to each antigen. In total 253 children received PENTA vaccine: 86 at 12 months, 85 at 15 months and 82 at 18 months. Injection site redness and swelling were least extensive in the youngest group (p < 0.001) but their rates of occurrence did not differ with age. Anti-PRP levels were similar in each age group prior to immunization; post-booster geometric mean concentrations (GMCs) ranged from 13.0 microg/ml in the youngest to 33.9 microg/ml in the oldest subjects (p < 0.0001). For each of the other antigens examined, booster responses were strongest at 18 months. We conclude that anti-PRP levels are stable between 12 and 18 months in children previously given PRP-T vaccine. PENTA boosters given at 12 months appear to cause milder injection site morbidity whereas those given at 18 months result in stronger responses to virtually every constituent antigen, although each age group responded satisfactorily.

Safety and immunogenicity of a combined diphtheria-tetanus-acellular pertussis-inactivated polio vaccine-Haemophilus influenzae type b vaccine administered at 2-4-6-13 or 3-5-12 months of age

METHODS

In an open randomized study we compared the safety and immunogenicity of two schedules for priming and booster vaccinations of infants. A pentavalent combination vaccine, including a lyophilized Haemophilus influenzae type b-tetanus toxoid conjugate vaccine reconstituted with a liquid diphtheria, tetanus, acellular pertussis (pertussis toxoid and filamentous hemagglutinin) and inactivated polio vaccine (DTaP-IPV/Act-HIB; Pasteur Mérieux Connaught, Lyon, France) was administered to 236 Swedish infants either at 2, 4 and 6 months or at 3 and 5 months, and a booster dose was administered 7 months after the last primary dose. Adverse events were monitored by diaries for 3 days after each vaccination and by questions at the ensuing visits. Antibodies against the different vaccine components were analyzed after the primary series of vaccinations, before and after the booster injections.

RESULTS

There were no serious adverse reactions, and the rates of febrile events and local reactions were low in both groups. The three dose primary schedule induced higher geometricmean concentrations for all antigens than did the two dose schedule, but there were no differences between the groups in proportions with protective antibody titers against diphtheria, tetanus, Hib and polio or in proportions with certain defined levels of pertussis antibodies. Prebooster results showed a similar pattern, with the exception that the group primed with three injections showed higher proportions of infants with detectable antibodies against polio-virus types 1 and 3. After booster vaccinations there were no differences between the two schedules in geometric mean or in proportions with antibodies above defined antibody concentrations, indicating effective priming from both primary series of vaccinations. Conclusion. The combined vaccine DTaP-IPV/ Act-HIB vaccine was equally safe and immunogenic when administered according to both time schedules studied.

Early immunization with conjugate vaccines

Conjugate vaccines have been used during the neonatal period or in early infancy in order to test their safety and immunologic behaviour. Adverse events even in neonates and premature babies have been mild and spontaneously resolving. Anticapsular antibody concentrations after first doses of Hib conjugates in early infancy are generally low, but analysis of responses clearly demonstrates active antibody production. Concentrations after the whole primary series are at or close to the level achieved in routine vaccination programmes. Noteworthy, immunologic memory seems to be induced already by first doses during newborn period. These data suggest that protection against invasive Hib infections may be achieved early in life.

Randomised trial of the effect of co-administration with acellular pertussis DTP vaccine on immunogenicity of Haemophilus influenzae type b conjugate vaccine

BACKGROUND

Inclusion of new vaccines in vaccination programmes for children would be easier if they could be combined with existing vaccines. Vaccines containing acellular pertussis in the diphtheria/tetanus/pertussis (DTP-a) combination are expected to replace the conventional whole-cell vaccines (DTP-w). We tested the immunogenicity and safety of a combination of DTP-a with the Haemophilus influenzae type b (Hib) conjugate of Hib capsular polysaccharide and tetanus toxid (PRP-T), and inactivated poliovirus vaccine (i.p.v.).

METHODS

120 infants were enrolled and randomised to four groups to receive DTP-a at ages 2, 4, and 6 months. At 4 and 6 months they also received Hib conjugate and i.p.v., either as separate injections or mixed with DTP-a. All injections were given intramuscularly in the anterolateral area of the thigh. Any reactions after each vaccination were noted by the parents. EIA was used to measure titres of diphtheria, tetanus, and pertussis antibodies, RIA for Hib anticapsular antibodies, and microneutralisation assay for poliovirus antibodies from serum samples collected at the ages of 2, 4, 6, and 7 months.

FINDINGS

There were 30 infants in each group. Only mild adverse events were reported. There was a tendency towards slightly lower concentrations of filamentous haemagglutinin, tetanus, and poliovirus 1 antibodies when the vaccines were mixed. However, there was a more pronounced difference (p = 4 x 10(-6)) in Hib antibodies between groups receiving Hib capsular polysaccharide mixed with DTP-a (geometric mean concentrations 0.37 microgram/mL and 0.56 microgram/mL) compared with groups receiving the vaccines separately (3.10 micrograms/mL and 3.94 micrograms/mL).

INTERPRETATION

Administration of premixed DTP-a, Hib conjugate, and i.p.v. affect the immune response significantly. The mechanism of this interference is not clear. The immunogenicity of all antigens must be tested before new combinations can be accepted for vaccination programmes for infants.