Priming effect, immunogenicity and safety of an Haemophilus influenzae type b-tetanus toxoid conjugate (PRP-T) and diphtheria-tetanus-acellular pertussis (DTaP) combination vaccine administered to infants in Belgium and Turkey

Factors That Influence the Immune Response to Vaccination

There is substantial variation between individuals in the immune response to vaccination. In this review, we provide an overview of the plethora of studies that have investigated factors that influence humoral and cellular vaccine responses in humans. These include intrinsic host factors (such as age, sex, genetics, and comorbidities), perinatal factors (such as gestational age, birth weight, feeding method, and maternal factors), and extrinsic factors (such as preexisting immunity, microbiota, infections, and antibiotics). Further, environmental factors (such as geographic location, season, family size, and toxins), behavioral factors (such as smoking, alcohol consumption, exercise, and sleep), and nutritional factors (such as body mass index, micronutrients, and enteropathy) also influence how individuals respond to vaccines. Moreover, vaccine factors (such as vaccine type, product, adjuvant, and dose) and administration factors (schedule, site, route, time of vaccination, and coadministered vaccines and other drugs) are also important. An understanding of all these factors and their impacts in the design of vaccine studies and decisions on vaccination schedules offers ways to improve vaccine immunogenicity and efficacy.

Immunogenicity and safety of a combined DTPa-IPV/Hib vaccine administered as a three-dose primary vaccination course in healthy Korean infants: phase III, randomized study

We assessed the immunogenicity and safety of a three-dose primary vaccination schedule with the combined diphtheria-tetanus-acellular pertussis-inactivated poliovirus/Haemophilus influenzae type b vaccine (DTPa-IPV/Hib) in Korean infants. In this phase III open-label, multicenter study (NCT01309646), healthy infants aged 42-69 days (randomized 1:1) received three doses of either pentavalent DTPa-IPV/Hib (DTPa-IPV/Hib group) or DTPa-IPV and Hib vaccines administered separately (DTPa-IPV+Hib group) at 2, 4, 6 months of age. The primary objective was to demonstrate non-inferiority of DTPa-IPV/Hib compared to DTPa-IPV+Hib vaccines in terms of immune responses to all vaccine antigens, 1 month post-dose 3. Solicited symptoms (local and general) were recorded during 4 days, and unsolicited adverse events (AEs) during 31 days, after each vaccination. Serious AEs (SAEs) were recorded throughout the study duration. The immunogenicity of the pentavalent DTPa-IPV/Hib vaccine was non-inferior compared to concomitant administration of DTPa-IPV+Hib vaccines. One month post-dose 3, nearly all infants had antibody levels above the seroprotective thresholds for anti-diphtheria toxoid, anti-tetanus toxoid, anti-polyribosyl-ribitol phosphate, and anti-poliovirus type 1, 2 and 3, and had antibody levels above the seropositive thresholds for anti-pertussis toxoid (PT), anti-filamentous hemagglutinin (FHA) and anti-pertactin (PRN) antibodies. A vaccine response for PT, FHA and PRN was observed in at least 96.7% of study participants. Anti-PRP geometric mean concentrations appeared lower for the DTPa-IPV/Hib group (8.456 µg/mL) than for the DTPa-IPV+Hib group (18.700 µg/mL). In both groups, the most common solicited symptoms were injection site redness and irritability. Fifty-seven SAEs were reported throughout the study; none were considered to be vaccination related.

Delayed adaptive immunity is related to higher MMR vaccine-induced antibody titers in children

There are notable inter-individual variations in vaccine-specific antibody responses in vaccinated children. The aim of our study was to investigate whether early-life environmental factors and adaptive immune maturation prior and close to measles–mumps–rubella (MMR) immunization relate to magnitudes of vaccine-specific antibody titers. In the FARMFLORA birth cohort, including both farming and non-farming families, children were immunized with the MMR vaccine at 18 months of age. MMR vaccine-induced antibody titers were measured in plasma samples obtained at 36 months of age. Infants' blood samples obtained at birth, 3–5 days and at 4 and 18 months of age were analyzed for T- and B-cell numbers, proportions of naive and memory T and B cells, and fractions of putative regulatory T cells. Multivariate factor analyses show that higher anti-MMR antibody titers were associated with a lower degree of adaptive immune maturation, that is, lower proportions of memory T cells and a lower capacity of mononuclear cells to produce cytokines, but with higher proportions of putative regulatory T cells. Further, children born by cesarean section (CS) had significantly higher anti-measles titers than vaginally-born children; and CS was found to be associated with delayed adaptive immunity. Also, girls presented with significantly higher anti-mumps and anti-rubella antibody levels than boys at 36 months of age. These results indicate that delayed adaptive immune maturation before and in close proximity to immunization seems to be advantageous for the ability of children to respond with higher anti-MMR antibody levels after vaccination.

Earlier infantile immune maturation is related to higher DTP vaccine responses in children

There are large inter-individual variations in vaccine-specific antibody responses in children. We sought to investigate whether early-life environmental factors and/or adaptive immune maturation were related to diphtheria–tetanus–pertussis (DTP) vaccine-specific antibody levels at 18 months of age. In the prospective FARMFLORA birth-cohort, including both farming and non-farming families, children were immunized with DTP vaccine at 3, 5 and 12 months of age. DTP vaccine-induced antibody levels were measured in plasma at 18 months of age. Infants' blood samples obtained at birth, 3–5 days, 4, 18 and 36 months and at 8 years of age were analyzed for total CD4⁺ T- and B-cell counts, proportions of naïve and memory T and B cells, and fractions of putative regulatory T cells by flow cytometry. Multivariate factor analysis was used to examine associations between immune variables and vaccine responses. The most apparent multivariate pattern was that higher anti-DTP antibody titers at 18 months of age were associated with lower infantile total counts of T and B cells in the blood. Furthermore, lower infantile total T- and B-cell blood counts were associated with higher proportions of circulating CD45RO⁺ memory T cells and to lower proportions of α4β7⁺ naïve T cells later in childhood. The multivariate findings were corroborated in univariate correlation analyses. Sex, delivery mode and dairy farm exposure were unrelated to the magnitude of DTP-specific antibody responses. Our results thus suggest that children with a more mature/activated infantile adaptive immunity respond with higher vaccine-induced anti-DTP antibody levels at 18 months of age.

Acellular pertussis vaccines and the role of pertactin and fimbriae

The introduction of acellular pertussis (Pa) vaccines in countries with a low uptake of whole-cell pertussis (Pw) vaccines has led to a dramatic reduction in pertussis disease. Diphtheria-tetanus-acellular pertussis (DTPa) vaccines have also ensured continued high level disease protection in these countries following the shift from Pw- to Pa-containing vaccines, and allowed pertussis booster programs to be implemented. Vaccines containing between one and five components have been licensed and implemented. Those with three or more components consisting of filamentous hemagglutinin (FHA), pertussis toxin (PT) and pertactin (PRN) are considered to be more effective than one/two-component Pa vaccines that contain only PT or both PT and FHA. Changes in circulating Bordetella pertussis strains may impact vaccine efficacy and, thus, incidence and transmission of pertussis and deserve to be followed carefully. To date, vaccine-induced shifts among fimbriae (FIM) are reported and this could impact the efficacy of FIM-containing vaccines. Currently, FIM3 appears to be dominant in most European countries, Canada and Australia. Data obtained from a DTPa5 vaccine containing FIM2 and FIM3 have indicated a shift towards an increase in FIM3-expressing B. pertussis clinical breakthrough cases when compared with control vaccine. By contrast, relatively minor PT and PRN sequence polymorphisms have been identified without demonstrable association with vaccination programs. Adsorption of PRN to aluminum salt appears critical for optimal protective capacity in murine pertussis lung challenge. In addition, clinical studies have shown anti-PRN antibody levels to be higher when PRN is adsorbed at a 8-microg dosage versus non-adsorbed PRN at a 3-microg dosage. The available data, therefore, demonstrate that appropriately formulated acellular vaccines containing PT and PRN are the preferred option for pertussis immunization.

Comparing Haemophilus influenzae type b conjugate vaccine schedules: a systematic review and meta-analysis of vaccine trials

BACKGROUND

The optimal schedule and the need for a booster dose are unclear for Haemophilus influenzae type b (Hib) conjugate vaccines. We systematically reviewed relative effects of Hib vaccine schedules.

METHODS

We searched 21 databases to May 2010 or June 2012 and selected randomized controlled trials or quasi-randomized controlled trials that compared different Hib schedules (3 primary doses with no booster dose [3p+0], 3p+1 and 2p+1) or different intervals in primary schedules and between primary and booster schedules. Outcomes were clinical efficacy, nasopharyngeal carriage and immunological response. Results were combined in random-effects meta-analysis.

RESULTS

Twenty trials from 15 countries were included; 16 used vaccines conjugated to tetanus toxoid (polyribosylribitol phosphate conjugated to tetanus toxoid). No trials assessed clinical or carriage outcomes. Twenty trials examined immunological outcomes and found few relevant differences. Comparing polyribosylribitol phosphate conjugated to tetanus toxoid 3p+0 with 2p+0, there was no difference in seropositivity at the 1.0 μg/mL threshold by 6 months after the last primary dose (combined risk difference -0.02; 95% confidence interval: -0.10, 0.06). Only small differences were seen between schedules starting at different ages, with different intervals between primary doses, or with different intervals between primary and booster doses. Individuals receiving a booster were more likely to be seropositive than those at the same age who did not.

CONCLUSIONS

There is no clear evidence from trials that any 2p+1, 3p+0 or 3p+1 schedule of Hib conjugate vaccine is likely to provide better protection against Hib disease than other schedules. Until more data become available, scheduling is likely to be determined by epidemiological and programmatic considerations in individual settings.

Variation between Populations in the Innate Immune Response to Vaccine Adjuvants

The success of the World Health Organization recommended “Expanded Program of Immunization” (EPI) and similar regional or national programs has been astounding. However, infectious threats currently not covered by these programs continue to infect millions of infants around the world. Furthermore, many infants do not receive existing vaccines either on time or for the required number of doses to provide optimal protection. Nor do all infants around the world develop the same protective immune response to the same vaccine. As a result approximately three million infants die every year from vaccine preventable infections. To tackle these issues, new vaccines need to be developed as well as existing ones made easier to administer. This requires identification of age-optimized vaccine schedules and formulations. In order to be most effective this approach will need to take population-based differences in response to vaccines and adjuvants into account. This review summarizes what is currently known about differences between populations around the world in the innate immune response to existing as well as new and promising vaccine adjuvants.

Immunogenicity of a Haemophilus influenzae type b-tetanus conjugate vaccine when administered separately or in combined vaccines for primary immunization in two consecutive national schedules in Turkey

BACKGROUND

In Turkey, the Haemophilus influenzae type b-tetanus toxoid conjugate vaccine (Hib) was replaced by the combined diphtheria-tetanus-acellular pertussis and inactivated polio vaccine (DTaP-IPV/Hib) in 2008. This shift to the new schedule created different cohorts of vaccinated children as a consequence of the different schedules used. We evaluated the immunogenicity of the Hib vaccine in infants vaccinated with these different schedules.

METHODS

Three groups of children were evaluated: group 1 comprised 145 infants vaccinated with diphtheria, tetanus, and whole cell pertussis (DTwP), oral polio vaccine (OPV), and Hib vaccines simultaneously at separate sites; group 2 comprised 204 infants vaccinated with the DTaP-IPV/Hib combined vaccine; group 3 comprised 100 infants vaccinated with a mixed schedule of DTwP, OPV, and Hib for the first one or two doses, followed by DTaP-IPV/Hib vaccine to complete the series.

RESULTS

Anti-polyribosylribitol phosphate (anti-PRP) titers ≥0.15μg/ml were similar in groups 1, 2, and 3. However, in group 1, who received all the vaccines at separate sites, ≥ l.0μg/ml long-lasting antibody titers and anti-PRP geometric mean titers were higher (p=0.001).

CONCLUSION

This study showed that even one dose administered in combination with other vaccines in a primary series decreased the level of anti-PRP.

International Bordetella pertussis assay standardization and harmonization meeting report. Centers for Disease Control and Prevention, Atlanta, Georgia, United States, 19-20 July 2007

An international meeting on Bordetella pertussis assay standardization and harmonization was held at the Centers for Disease Control and Prevention (CDC), Atlanta, GA, 19–20 July 2007. The goal of the meeting was to harmonize the immunoassays used for pertussis diagnostics and vaccine evaluation, as agreed upon by academic and government researchers, regulatory authorities, vaccine manufacturers, and the World Health Organization (WHO).

The primary objectives were (1) to provide epidemiologic, laboratory, and statistical background for support of global harmonization; (2) to overview the current status of global epidemiology, pathogenesis and immunology of pertussis; (3) to develop a consensus opinion on existing gaps in understanding standardization of pertussis assays used for serodiagnosis and vaccine evaluation; and (4) to search for a multicenter process for addressing these priority gaps. Presentations and discussions by content experts addressed these objectives. A prioritized list of action items to improve standardization and harmonization of pertussis assays was identified during a group discussion at the end of the meeting. The major items included: (1) to identify a group that will organize, prepare, maintain, and distribute proficiency panels and key reagents such as reference and control sera; (2) to encourage the development and identification of one or more reference laboratories that can serve as an anchor and resource for other laboratories; (3) to define a performance-based assay method that can serve as a reference point for evaluating laboratory differences; (4) to develop guidance on quality of other reagents, e.g., pertussis toxin and other antigens, and methods to demonstrate their suitability; (5) to establish an international working group to harmonize the criteria to evaluate the results obtained on reference and proficiency panel sera; (6) to create an inventory to determine the amount of appropriate and well-characterized sera that are available globally to be used as bridging reagents for vaccine licensure; and (7) to seek specific guidance from regulatory authorities regarding the expectations and requirements for the licensure of new multicomponent pertussis vaccines.

Interchangeability of a hepatitis A vaccine second dose: Avaxim 80 following a first dose of Vaqta 25 or Havrix 720 in children in Turkey

INTRODUCTION

This randomised, observer-blind clinical trial conducted in Turkey evaluated the immunogenicity, safety and interchangeability of three paediatric inactivated hepatitis A vaccines in 424 seronegative children between 1 and 15 years of age.

METHODS

Potential subjects were screened for anti-hepatitis A virus (HAV) antibodies prior to receiving a first dose of Avaxim 80, Havrix 720 or Vaqta 25, followed by a second dose of either the same vaccine or Avaxim 6 months later. Anti-HAV antibody concentrations were measured 2 weeks after the first injection, at 24 weeks (before the second dose) and at 28 weeks for the evaluation of the immune response.

RESULTS

Nearly 80% of the children between 1 and 5 years of age and half of those between the ages of 6 and 10 in the population from which the subjects were recruited were seronegative for HAV antibodies. Two weeks after the first dose, 98.2% of all subjects had anti-HAV antibody concentrations equal to or higher than 20 mIU/mL, believed to be seroprotective, and all subjects were seroprotected before and after the second dose. Anti-HAV geometric mean concentrations (GMCs) 2 weeks after the first dose and before the second were similar in children who received Avaxim and Vaqta (P = 0.2), but both were higher than Havrix (P < 0.01). There were no significant differences in the anti-HAV GMCs between the study groups that received two doses of the same vaccine compared with two doses of different vaccines. There were no significant differences in the frequency of any local or systemic adverse events among the study groups following either of the two doses.

CONCLUSION

All three vaccines are safe and highly immunogenic in healthy children aged 1 to 15 years. Avaxim 80 may also be given as the second dose when Havrix 720 or Vaqta 25 are given as the first dose. The pattern of seroprevalence seen here is similar to that reported in a number of recent evaluations in Turkey, and are supportive of the routine hepatitis A vaccination of young children.

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:

A liquid hexavalent combined vaccine against diphtheria, tetanus, pertussis, poliomyelitis, Haemophilus influenzae type B and hepatitis B: review of immunogenicity and safety

To reduce the number of injections needed to comply with paediatric vaccination requirements, a liquid, hexavalent vaccine (DTaP-IPV-PRP-T-HBs; Hexavac; Aventis Pasteur MSD) has been developed for primary and booster vaccination of infants and toddlers. In extensive clinical studies, Hexavac has been shown to be highly immunogenic. Seroconversion or seroprotective titres of antibodies against all antigens were achieved in the majority of infants following a primary series of three doses administered at 1-2-month intervals from 2 months of age. Hexavac also induced immunologic memory, as evidenced by the anamnestic response to booster vaccination at 12-18 months of age. These responses were comparable with those seen following concomitant administration of Pentavac (DTaP-IPV//PRP-T) and monovalent hepatitis B vaccine (H-B-Vax II), and were also within the ranges observed for other relevant licensed vaccines. Clinical studies comparing the immunogenicity of Hexavac administered at either 2, 3 and 4 months or 2, 4 and 6 months demonstrated that it can be used by either vaccination schedule. A further study also supported the use of primary doses of Hexavac at 3 and 5 months with a booster at 12 months of age. Hexavac demonstrated a good reactogenicity and tolerability profile. The most frequently reported adverse events after both primary and booster doses were local reactions of redness and swelling/induration and a systemic response of mild fever, irrespective of the vaccine used for priming. Hexavac provided immunity against six important childhood diseases with a single injection at each visit.

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.

Assessing efficacy of Haemophilus influenzae type b combination vaccines

Regulatory approval of diphtheria and tetanus toxoids and acellular pertussis (DTaP)-based combination vaccines containing Haemophilus influenzae type b (Hib) has been delayed in the US because of difficulty in assessing the effect of lower Hib immunogenicity on vaccine efficacy compared with the immunogenicity of the specific Hib component administered separately. Hib conjugate vaccines confer protection by eliciting serum anticapsular antibody and priming for immunologic memory. Therefore, compelling proof of efficacy would be demonstration that a combination vaccine primes for memory and elicits antibody responses that are not inferior to those elicited by other US-licensed Hib conjugate vaccines, not necessarily the specific Hib component used in the combination. Vaccinated infants also can be considered protected if their serum anticapsular antibody concentrations are > or =0.15 microg/mL immediately before the booster dose given in the second year of life, when antibody concentrations are lowest. These alternative serologic approaches offer a strong scientific and regulatory rationale for licensure of effective DTaP-based Hib combination vaccines.

Combination vaccines

The biotechnology revolution has stimulated vaccine development, blessing us with new, safe, and effective vaccines, but burdening our vaccination schedule. The incorporation of multiple individual vaccines into combination vaccines can simplify vaccine administration programs and permit the inclusion of new antigens in the vaccine schedule. Although the development, evaluation, and implementation of combination vaccines pose numerous challenges and raise controversies that remain unresolved, there is a reasonable prospect of United States licensure within the next few years of several new combination vaccines for infant use. Approval in the United States of combination vaccines in use elsewhere might be speeded by improved vaccination tracking systems and post marketing efficacy surveillance, which would provide confidence that material reductions in efficacy could be detected following licensure, and thereby ease concerns regarding moderate, but perhaps immaterial, declines in immunogenicity seen with some combinations.

Principles of pediatric combination vaccines and practical issues related to use in clinical practice

BACKGROUND

During the past two decades the number of injections that are required per office visit to fulfill the recommended childhood immunization schedule has increased dramatically.

METHODS

By reviewing the literature, the principles associated with pediatric combination vaccines are discussed, and practical issues related to their use in clinical practice are evaluated.

RESULTS

The ideal combination vaccine is safe, effective and easy to store and use, and its antigenic components fit within the recommended immunization schedule. The ideal combination is associated with fewer adverse reactions than the separately administered antigens, with improved efficacy and higher immune responses compared with its component vaccines. An acceptable combination vaccine must provide comparable efficacy and safety to its component vaccines. Although there are a limited number of combination vaccines already available [diphtheria-tetanus-pertussis, inactivated poliovirus vaccine (IPV) and measles-mumps-rubella], effort is being focused on combining these vaccines with other routine vaccines of infancy including Haemophilus influenzae type b (Hib) and hepatitis B vaccine (HepB). Currently under review by the Food and Drug Administration are diphtheria-tetanus-acellular pertussis (DTPa)-HepB-IPV and DTPa-Hib-IPV combination vaccines, and two DTPa-HepB-IPV-Hib vaccines have been licensed in Europe. As more combination vaccines become available, issues such as interchangeability and administration of extra doses are raised; however, it is important not to miss a vaccination opportunity.

CONCLUSIONS

The number of injections required to fulfill the recommended childhood immunization schedule at each visit creates problems for patients and practitioner, sometimes risking a missed opportunity for vaccination. The development of combination vaccines will circumvent this problem and increase compliance and vaccination coverage rates.

Early responses to nonconjugated polyribosylribitol phosphate challenge as evidence of immune memory after combined diphtheria-tetanus-pertussis-polio-Haemophilus influenzae type b primary vaccination

OBJECTIVES

A high risk of invasive Haemophilus influenzae type b (Hib) disease exists in the first few years of life. A reduction in anti-polyribosylribitol phosphate (PRP) antibody concentrations follows the administration of certain diphtheria-tetanus-acellular pertussis (DTPa)-based Hib conjugate combined vaccines. However, these combined vaccines prime the immune memory, which is an important factor in protection. As yet there is no direct evidence of the time scale involved in the development of the immune memory post-primary vaccination. In this report we investigated the presence of immune memory at 10 and 12 months of age, 4 and 6 months after primary vaccination of young infants with a pentavalent combination of DTPa, inactivated poliovirus vaccine (IPV) and Hib (DTPa-IPV/Hib) vaccine.

METHODS

In two trials (A and B) infants received DTPa-IPV combined with Hib-tetanus conjugate (PRP-T) vaccine at 2, 4 and 6 months of age. The presence of immune memory was assessed by measuring anti-PRP concentrations 7 to 10 days after a nonconjugated PRP challenge given at 10 months in Trial A and at 12 months in Trial B.

RESULTS

Administration of a nonconjugated PRP challenge 4 and 6 months after primary vaccination in Trials A and B, respectively, elicited an increase in anti-PRP geometric mean concentrations (4.5 and 5.8 microg/ml, respectively) within 7 to 10 days. These concentrations exceed those reported in the literature involving unprimed children who had received a single dose of nonconjugated PRP at the same age.

CONCLUSION

The results demonstrate the development of anti-PRP immune memory at an early age, 4 and 6 months after completion of a three dose primary vaccination course of combined DTPa-IPV/Hib vaccine. The ability of primed infants to mount a rapid response is an important observation given the high risk of Hib infection at this critical age.

Combination vaccines

The past decade has shown a marked increase in the number of vaccines currently licensed and recommended for use in infants and children. Although most agree that it is desirable to combine as many of these vaccines as possible into a single injection, safety and efficacy must not be sacrificed. Clearly, a resurgence in Hib meningitis or measles (for example) would not be an acceptable price for the convenience of a single injection; but it is not clear how large a reduction in immunogenicity can be incurred without paying such a price. This conundrum has slowed the licensure of useful combination vaccines, despite a consensus that parents and practitioners have reached a limit to the number of injections they will deliver to young children. We anticipate US licensure for infant use of (at least) one DTaP-IPV-Hib vaccine and one DTaP-IPV-HB vaccine within the next few years, given the apparent lack of material reduction in immunogenicity of these specific combination products. Licensure in the United States of some of the other combinations now used in Europe is also possible, given supporting national surveillance data or improvements in our understanding of the correlates of immunity. Enhanced vaccination tracking systems and postmarketing efficacy surveillance should provide confidence that material reductions in efficacy could be detected following licensure, and thereby ease the approval of combinations that result in moderate, but perhaps immaterial, declines in immunogenicity.

Immunologic correlates of protection induced by vaccination

Vaccine design and licensing depend on the choice of protective antigens and the demonstration of their efficacy. Ideally efficacy correlates with some measurement of immune response, although occasionally the correlation is weak and in the case of some vaccines uncertain. This paper attempts to review what is known about correlates of vaccine-induced protection. Although mucosal and cellular immune responses are clearly important to protection by some vaccines, most vaccines licensed today depend for their efficacy on serum antibodies. Particular levels of antibodies can be identified that confer protection most of the time. A condition for the efficacy of antibodies is functionality, i.e. their ability to kill or inactivate pathogens. The immune system is redundant, and the different types of responses to vaccines act synergistically.

Immunogenicity and safety of a new liquid hexavalent combined vaccine compared with separate administration of reference licensed vaccines in infants

OBJECTIVE

The immunogenicity and safety of a new liquid hexavalent vaccine (diphtheria-tetanus-acellular pertussis-inactivated polio vaccine-hepatitis B-polyribosyl ribitol phosphate conjugated to tetanus protein; Hexavac; Aventis Pasteur MSD, Lyon, France) are compared with those of reference vaccines [diphtheria-tetanus-acellular pertussis-inactivated polio vaccine reconstituting lyophilized purified Haemophilus influenzae polysaccharide conjugated to tetanus protein vaccine (Pentavac; Aventis Pasteur MSD) and hepatitis B vaccine (H-B-Vax II; Aventis Pasteur MSD)] injected separately at the same visit in a prospective multicenter, comparative, open label trial.

METHODS

Infants were randomized to receive Hexavac (n = 423) or Pentavac and H-B-Vax II (n = 425) as a primary immunization series at 2, 4 and 6 months of age. Seroprotection and seroconversion rates against all antigens at 1 month after the primary series were compared between the two vaccine groups with 95% confidence intervals (CI0.95) and were considered clinically equivalent (not inferior) when the upper limit of the 95% confidence interval on the difference (reference, hexavalent) was below predefined differences.

RESULTS

Hexavac met and surpassed the pre-defined criteria for clinical equivalence to Pentavac and H-B-Vax II given concomitantly. It elicited similar seroprotection and seroconversion rates against all antigens. Seroprotection and seroconversion rates obtained 1 month after the third dose of Hexavac were >90% for all antigens. The postimmunization antibody geometric mean titers (GMT) for hepatitis B and purified Haemophilus influenzae polysaccharide were about 2-fold higher in infants who received the reference vaccines than in infants who had received Hexavac. GMTs for poliovirus antibodies tended to be enhanced in infants vaccinated with Hexavac. GMTs for all other antigens were very similar among both groups. Hexavac was generally well-tolerated. At least one local reaction was reported in 20.3% of Hexavac injections compared with 15.8% at the Pentavac injections site and 3.8% at the H-B-Vax II injections site. These reactions were generally mild and transient. At least one systemic adverse event was reported in 45.7% of Hexavac injections compared with 42.2% of Pentavac and H-B-Vax II injections (mild fever, irritability and drowsiness were most frequently reported). The frequency of adverse events was not significantly different between groups. No vaccine-related serious adverse event occurred during the study.

CONCLUSION

This liquid hexavalent vaccine was generally well-tolerated and provided immune responses adequate to be protective against six infectious diseases with a single injection, given at 2, 4 and 6 months of age.

Associated or combined vaccination of Brazilian infants with a conjugate Haemophilus influenzae type b (Hib) vaccine, a diphtheria-tetanus-whole-cell pertussis vaccine and IPV or OPV elicits protective levels of antibodies against Hib

This study investigated the immunogenicity and safety of including a Haemophilus influenzae type b vaccine (polyribosylribitol phosphate conjugated to tetanus toxoid, PRP-T) in three different vaccination schemes: (1) PRP-T reconstituted with a combined diphtheria-tetanus-pertussis-inactivated poliovirus vaccine (DTP-IPV//PRP-T); (2) PRP-T reconstituted with DTP and administered concomitantly with an oral poliovirus vaccine (DTP//PRP-T+OPV); and (3) PRP-T administered concomitantly with DTP at a different injection site and OPV (DTP+PRP-T+OPV). Vaccines were given at 2, 4, and 6 months of age. A total of 252 infants were enrolled, and randomly assigned to one of the three vaccination groups (84 infants in each group); 241 infants were followed until the end of the study. Antibody production against PRP, diphtheria, tetanus and pertussis antigens was satisfactory for each vaccination scheme used. A good response to Hib vaccine was elicited in each group, and 3 months after the third vaccine dose, at least 97% of children in each group had levels of PRP antibody considered to be seroprotective (>0.15 microg/ml), and over 90% of children in each group had levels over 1. 0 microg/ml. The solicited local and systemic adverse events following vaccination were mild in all groups and resolved within 4 days without medical intervention. With the exception of fever, which was more common after the second dose in children who received DTP-IPV//PRP-T, local and systemic reactions did not differ between the vaccination groups. Due to the practical advantages of combined vaccines, their use in routine immunization programs in developing countries is highly desirable. Our results show that Hib conjugate vaccine can be included in routine immunization programs that include either OPV or IPV with satisfactory immunogenicity and safety profiles. This flexible approach should facilitate the inclusion of the Hib conjugate vaccine in routine immunization programs on a world-wide scale.

Primary vaccination of infants with diphtheria-tetanus-acellular pertussis-hepatitis B virus- inactivated polio virus and Haemophilus influenzae type b vaccines given as either separate or mixed injections

OBJECTIVE

The aim of this open, multicenter, randomized trial was to evaluate the immunogenicity and reactogenicity of a candidate combined diphtheria-tetanus-acellular pertussis-hepatitis B virus-inactivated polio virus (DTaP-HBV-IPV) vaccine when given as either a mixed or as separate concomitant injections with Haemophilus influenzae type b (Hib) vaccine.

STUDY DESIGN

A total of 359 subjects were randomized to receive either DTaP-HBV-IPV/Hib (mixed administration - 180 subjects) or DTaP-HBV-IPV + Hib (separate administration in opposite limbs - 179 subjects) at 2, 3, and 4 months of age.

RESULTS

After vaccination, seroprotective antibody concentrations against diphtheria, tetanus, hepatitis B, and polio viruses and a high (> or = 97%) pertussis vaccine response were seen in almost all study participants. All subjects except one in the mixed administration group had postvaccination Hib anti-PRP antibody concentrations > or = 0.15 microg/mL. Of subjects in the mixed and separate group, 77.2% (geometric mean antibody concentration, 2. 62 microg/mL) and 88.6% (geometric mean antibody concentration, 4.45 microg/mL) had Hib anti-PRP concentrations > or = 1 microg/mL, respectively. The addition of the Hib component to the 5-component vaccine did not increase the incidence of local or general reactions.

CONCLUSION

Both administrations of the candidate vaccine were found to be safe, immunogenic, and well tolerated. Although anti-PRP geometric mean antibody concentrations and the percent of subjects achieving the 1 microg/mL seroprotective level were lower after the mixed administration, they were in the range seen with monovalent Hib vaccines or with other DTaP-based/Hib combinations licensed in some European countries. Therefore both administrations have the potential to simplify childhood immunization.

Absence of a significant interaction between a Haemophilus influenzae conjugate vaccine combined with a diphtheria toxoid, tetanus toxoid and acellular pertussis vaccine in the same syringe and inactivated polio vaccine

BACKGROUND

We compared the antibody response to Haemophilus influenzae type b capsular polysaccharide (PRP) after three doses of a diphtheria toxoid, tetanus toxoid and acellular pertussis vaccine (DTaP) combined with a PRP-tetanus conjugate (PRP-T) in infants randomized to receive oral polio vaccine (OPV) or inactivated polio vaccine (IPV). The polio vaccine was given separately at the same visit.

METHODS

Three hundred fifty-six infants from pediatric practices in suburban Chicago and New Orleans were randomized into two groups. Group A received OPV at 2 and 4 months of age; Group B received IPV at 2 and 4 months of age. Both groups received DTaP/PRP-T at 2, 4 and 6 months of age and hepatitis B vaccine at 2 and 4 months of age. A serum sample was obtained before immunization (age 2 months) and 1 month after 3 doses of DTaP/PRP-T (age 7 months). Sera were assayed for antibody responses to all relevant vaccine antigens.

RESULTS

No significant vaccine antigen interference was found when polio immunization was provided by IPV or OPV for anti-PRP, diphtheria, tetanus or pertussis antibodies. OPV recipients had a significantly higher mean antibody response to serotype 1 (P = 0.03) and 2 (P = 0.0001) poliovirus.

CONCLUSION

Whether polio immunization was accomplished with IPV or OPV did not significantly influence the antibody responses in sera obtained at 7 months of age for anti-PRP, anti-diphtheria and anti-tetanus toxoid antibodies and antibodies to pertussis antigens, when DTaP/PRP-T was given in the primary series.

Combined vaccination of Haemophilus influenzae type b conjugate and diphtheria-tetanus-pertussis containing acellular pertussis

After the introduction of effective Haemophilus influenzae type b (Hib) conjugate vaccines, clinical practice has driven the development of combination vaccines comprising Hib conjugates with the infant diphtheria-tetanus-pertussis (DTP) vaccines. However, when such combinations contain an acellular pertussis component (Pa), the antibody response to Hib is lower than that with separate injections and doubts have been raised about their efficacy. We believe that such concerns are unwarranted, since the serological correlates of efficacy previously applied for Hib polysaccharide vaccines seem inappropriate for Hib conjugates. Furthermore, our own studies have shown that the lower antibody responses are not associated with impaired function of the antibodies induced, nor, and possibly more importantly, with the induction of immune memory against Hib. Therefore, with the proviso that careful clinical surveillance of Hib disease is maintained, we encourage the introduction of DTPa-Hib combinations to facilitate the inclusion of Hib into the already crowded childhood immunisation schedule.

Immunogenicity study of a combined diphtheria, tetanus, acellular pertussis, inactivated poliomyelitis vaccine used to reconstitute a freeze-dried Haemophilus influenzae type b vaccine (DTaP-IPV//PRP-T) administered simultaneously with a hepatitis B vaccine at two, three and four months of life

This study was designed to assess the immunogenicity of a vaccine combining diphtheria and tetanus toxoids, acellular pertussis vaccine, and inactivated poliovirus vaccine reconstituting Haemophilus influenzae type b polysaccharide conjugated to tetanus protein (DTaP-IPV//PRP-T; Pasteur Mérieux Connaught, Lyon, France) administered simultaneously in association with hepatitis B vaccine (RECOMBIVAX (¿trade mark omitted¿) Merck, Sharp & Dohme, West Point, PA, USA) for the primary immunization of infants. The vaccines were administered at two, three and four months of age. One hundred and sixty-two healthy infants, aged 8-10 weeks, were enrolled in the study. Blood samples were taken before the first dose and 4 weeks after the third dose. The infants were observed for 15 minutes after vaccination for any immediate reaction. Adverse events requiring a medical consultation were recorded by the parents in a diary over the 7 days following vaccination. Four weeks after the third immunization, the percentages of infants fulfilling seroconversion criteria were 98.9% for pertussis toxin, 95.9% for filamentous haemagglutinin, 100.0% for tetanus, 100.0% for diphtheria, 99.3% for poliovirus type 1, 100.0% for both poliovirus types 2 and 3, 98.0% for Haemophilus influenzae type b, and 100% for hepatitis B surface antigen. No vaccine-related serious adverse event was reported. The simultaneous administration of DTaP-IPV//PRP-T and hepatitis B vaccines at two, three and four months of age yielded clinically satisfactory immune responses to all antigens compared with historical controls and gave a good safety profile.