George R. Siber

Efficacy, safety and immunogenicity of heptavalent pneumococcal conjugate vaccine in children.

Objective. To determine the efficacy, safety and immunogenicity of the heptavalent CRM197 pneumococcal conjugate vaccine against invasive disease caused by vaccine serotypes and to determine the effectiveness of this vaccine against clinical episodes of otitis media. Methods. The Wyeth Lederle Heptavalent CRM197 (PCV) was given to infants at 2, 4, 6 and 12 to 15 months of age in a double blind trial; 37 868 children were randomly assigned 1:1 to receive either the pneumococcal conjugate vaccine or meningococcus type C CRM197 conjugate. The primary study outcome was invasive disease caused by vaccine serotype. Other outcomes included overall impact on invasive disease regardless of serotype, effectiveness against clinical otitis media visits and episodes, impact against frequent and severe otitis media and ventilatory tube placement. In addition the serotype‐specific efficacy against otitis media was estimated in an analysis of spontaneously draining ears. Results. In the interim analysis in August, 1998, 17 of the 17 cases of invasive disease caused by vaccine serotype in fully vaccinated children and 5 of 5 of partially vaccinated cases occurred in the control group for a vaccine efficacy of 100%. Blinded case ascertainment was continued until April, 1999. As of that time 40 fully vaccinated cases of invasive disease caused by vaccine serotype had been identified, all but 1 in controls for an efficacy of 97.4% (95% confidence interval, 82.7 to 99.9%), and 52 cases, all but 3 in controls in the intent‐to‐treat analysis for an efficacy of 93.9% (95% confidence interval, 79.6 to 98.5%). There was no evidence of any increase of disease caused by nonvaccine serotypes. Efficacy for otitis media against visits, episodes, frequent otitis and ventilatory tube placement was 8.9, 7.0, 9.3 and 20.1% with P < 0.04 for all. In the analysis of spontaneously draining ears, serotype‐specific effectiveness was 66.7%. Conclusion. This heptavalent pneumococcal conjugate appears to be highly effective in preventing invasive disease in young children and to have a significant impact on otitis media.

Which Pneumococcal Serogroups Cause the Most Invasive Disease: Implications for Conjugate Vaccine Formulation and Use, Part I

We analyzed >70 recent data sets to compare the serogroups causing invasive pneumococcal disease (IPD) with those represented in conjugate vaccine formulations. Five to 8 and 10-11 serogroups comprise at least 75% of pneumococcal isolates from young children and older children/adults, respectively, in each geographic region. Serogroups in the 7-valent formulation (4, 6, 9, 14, 18, 19, and 23) cause 70%-88% of IPD in young children in the United States and Canada, Oceania, Africa, and Europe, and <65% in Latin America and Asia. Serogroups in the 9-valent formulation (7-valent+1, 5) cause 80%-90% of IPD in each region except Asia (66%). Serogroup 1 accounts for >6% of IPD in each region, including Europe, except the United States and Canada and Oceania. In contrast, several serogroups not found in 7-, 9-, and 11-valent conjugate formulations are significant causes of disease in older children/adults. Nevertheless, each conjugate formulation could prevent a substantial IPD burden in each region and age group.

Adjuvants for human vaccines—current status, problems and future prospects☆

Adjuvants help antigen to elicit an early, high and long-lasting immune response with less antigen, thus saving on vaccine production costs. In recent years, adjuvants received much attention because of the development of purified, subunit and synthetic vaccines which are poor immunogens and require adjuvants to evoke the immune response. With the use of adjuvants immune response can be selectively modulated to major histocompatibility complex (MHC) class I or MHC class II and Th1 or Th2 type, which is very important for protection against diseases caused by intracellular pathogens such as viruses, parasites and bacteria (Mycobacterium). A number of problems are encountered in the development and use of adjuvants for human vaccines. The biggest issue with the use of adjuvants for human vaccines, particularly routine childhood vaccines, is the toxicity and adverse side-effects of most of the adjuvant formulations. At present the choice of adjuvants for human vaccination reflects a compromise between a requirement for adjuvanticity and an acceptable low level of side-effects. Other problems with the development of adjuvants include restricted adjuvanticity of certain formulations to a few antigens, use of aluminum adjuvants as reference adjuvant preparations under suboptimal conditions, non-availability of reliable animal models, use of non-standard assays and biological differences between animal models and humans leading to the failure of promising formulations to show adjuvanticity in clinical trials. The most common adjuvants for human use today are still aluminum hydroxide and aluminum phosphate, although calcium phosphate and oil emulsions also have some use in human vaccinations. During the last 15 years much progress has been made on development, isolation and chemical synthesis of alternative adjuvants such as derivatives of muramyl dipeptide, monophosphoryl lipid A, liposomes, QS21, MF-59 and immunostimulating complexes (ISCOMS). Other areas in adjuvant research which have received much attention are the controlled release of vaccine antigens using biodegradable polymer microspheres and reciprocal enhanced immunogenicity of protein-polysaccharide conjugates. Biodegradable polymer microspheres are being evaluated for targeting antigens on mucosal surfaces and for controlled release of vaccines with an aim to reduce the number of doses required for primary immunization. Reciprocal enhanced immunogenicity of protein-polysaccharide conjugates will be useful for the development of combination vaccines.

Efficacy and safety of seven-valent conjugate pneumococcal vaccine in American Indian children: group randomised trial

BACKGROUND Streptococcus pneumoniae is the main cause of invasive bacterial disease in children aged younger than 2 years. Navajo and White Mountain Apache children have some of the highest rates of invasive pneumococcal disease documented in the world. We aimed to assess the safety and efficacy of a seven-valent polysaccharide protein conjugate pneumococcal vaccine (PnCRM7) against such disease. METHODS In a group-randomised study, we gave this vaccine to children younger than 2 years from the Navajo and White Mountain Apache Indian reservations; meningococcal type C conjugate vaccine (MnCC) served as the control vaccine. Vaccine schedules were determined by age at enrollment. We recorded episodes of invasive pneumococcal disease and serotyped isolates. Analyses were by intention to treat and per protocol. FINDINGS 8292 children enrolled in the trial. In the per protocol analysis of the primary efficacy group (children enrolled by 7 months of age) there were eight cases of vaccine serotype disease in the controls and two in the PnCRM7 group; in the intention-to-treat analysis we noted 11 cases of vaccine serotype disease in the MnCC control group and two in the PnCRM7 group. After group randomisation had been controlled for, the per protocol primary efficacy of PnCRM7 was 76.8% (95% CI -9.4% to 95.1%) and the intention-to-treat total primary efficacy was 82.6% (21.4% to 96.1%). INTERPRETATION PnCRM7 vaccine prevents vaccine serotype invasive pneumococcal disease even in a high risk population. Other regions with similar disease burden should consider including this vaccine in the routine childhood vaccine schedule.

The Contribution of Specific Pneumococcal Serogroups to Different Disease Manifestations: Implications for Conjugate Vaccine Formulation and Use, Part II

To assess whether certain serogroups of Streptococcus pneumoniae are preferentially associated with specific disease manifestations, we analyzed all recent pneumococcal disease studies and assessed the relative frequency of isolation of each serogroup by clinical site (as a proxy for different disease states). In all age groups, serogroups 1 and 14 were more often isolated from blood, and serogroups 6, 10, and 23 were more often isolated from cerebrospinal fluid (CSF); in young children, serogroups 3, 19, and 23 were more often isolated from middle ear fluid (MEF). Serogroups represented in conjugate vaccines were isolated slightly less frequently from CSF than from blood or MEF. Nonetheless, serogroups in the 9-valent conjugate vaccine formulation still comprised approximately 75% of pneumococcal isolates from the CSF of young children in Europe and in the United States and Canada. These analyses indicate that pneumococcal conjugate vaccines could potentially prevent a substantial proportion of episodes of bacteremic disease, pneumonia, meningitis, and otitis media, especially in young children.

Adjuvant Properties of Aluminum and Calcium Compounds

It is likely that aluminum compounds will continue to be used with human vaccines for many years as a result of their excellent track record of safety and adjuvanticity with a variety of antigens. For infections that can be prevented by induction of serum antibodies, aluminum adjuvants formulated under optimal conditions are the adjuvants of choice. It is important to select carefully the type of aluminum adjuvant and optimize the conditions of adsorption for every antigen since the degree of adsorption of antigens onto aluminum adjuvants markedly affects immunogenicity. The mechanism of adjuvanticity of aluminum compounds includes formation of a depot at the site of injection from which antigen is released slowly; stimulation of immune-competent cells of the body through activation of complement, induction of eosinophilia, and activation of macrophages; and efficient uptake of aluminum-adsorbed antigen particles by antigen-presenting cells because of their particulate nature and optimal size (< 10 microns). Limitations of aluminum adjuvants include local reactions, production of IgE antibodies, ineffectiveness for some antigens, and inability to elicit cell-mediated immune responses especially cytotoxic T-cell responses. Calcium phosphate, which has adjuvant properties similar to aluminum adjuvants, has the potential advantages of being a natural component of the body and of not increasing IgE production. There is a need for alternative adjuvants, particularly for diseases in which cell-mediated immune responses are important for prevention or cure.

Serological criteria for evaluation and licensure of new pneumococcal conjugate vaccine formulations for use in infants

The World Health Organization (WHO) is undertaking a series of consultations on serological criteria for the evaluation and licensure of new formulations/combinations or different vaccination schedules of pneumococcal conjugate vaccines. The lack of a definitive serological correlate of protection and the multiplicity of antigens involved, especially since the clinical efficacy of most of the individual serotypes represented in the only licensed vaccine has not been established, are hindering the formulation of criteria for licensure of new formulations or combinations of the vaccine. This report analyses the various options with their relative merits and drawbacks and provides preliminary recommendations as guidance to regulatory agencies in evaluating these vaccines for the purposes of licensure. More detailed recommendations for production and control of pneumococcal conjugate vaccines, including criteria for evaluation for licensure, are currently being drafted.

Biodegradable microspheres as controlled-release tetanus toxoid delivery systems.

Purified tetanus toxoid, a high-molecular-weight protein, was entrapped within poly(L-lactic acid) (PLA) and poly(D,L-lactic/glycolic acid) (PLGA) microspheres prepared by either a solvent extraction or a solvent evaporation method carried out in a multiple emulsion system (water-in-oil-in-water). The physical integrity and antigenicity of the protein treated under different processing conditions were investigated. A reduction of antigenicity that was related to the percentage of aggregated protein was noticed under some experimental conditions. This partial loss of antigenicity was associated with the lyophilization process and affected by the nature of the organic solvent. All types of microspheres prepared with different molecular weight PLA and PLGA displayed a high protein-loading efficiency (> 80%) but their size was strongly influenced by polymer molecular weight (3000 versus 100,000). Protein release pattern was influenced by both polymer molecular weight and composition (PLA versus PLGA). A constant release pattern after an induction period of 10 days was observed for microspheres composed of high-molecular-weight polymers (PLA and PLGA). The release rate was lower from PLA microspheres than from PLGA microspheres. In contrast, a continuously increasing release rate preceded by a burst was observed for low-molecular-weight (3000) PLGA microspheres. Microencapsulated tetanus toxoid was significantly more immunogenic in mice than fluid toxoid as determined by IgG anti-tetanus antibody levels and neutralizing antibodies. However, the magnitude and duration of the antibody response did not differ significantly from a similar dose of aluminium phosphate-adsorbed toxoid. We conclude that microencapsulated tetanus toxoid shows significant adjuvant activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Safety and immunogenicity of heptavalent pneumococcal CRM197 conjugate vaccine in infants and toddlers.

OBJECTIVES The objectives of this study were (1) to determine the safety and immunogenicity of heptavalent pneumococcal CRM197 conjugate (PNCRM7) vaccine in infants and (2) to determine the effect of concurrent hepatitis B immunization during the primary series and the effect of concurrent diphtheria and tetanus toxoid and acellular pertussis [DTaP (ACEL-IMUNE)] and conjugate CRM197 Haemophilus influenzae type b [HbOC (HibTITER) immunization at time of the booster dose on the safety and immunogenicity of PNCRM7and these other concurrently administered vaccines. METHODS This was a randomized double-blinded study in 302 healthy infants in the Northern California Kaiser Permanente (NCKP) Health Plan. Infants received either PNCRM7 vaccine or meningococcal group C conjugate vaccine as a control at 2, 4 and 6 months of age and a booster at 12 to 15 months of age. Study design permitted the evaluation of immunology and safety of concurrent administration of routine vaccines. Antibody titers were determined on blood samples drawn before and 1 month after the primary series and the booster dose. RESULTS After the third dose of PNCRM7 geometric mean concentrations (GMCs) ranged from 1.01 for serotype 9V to 3.72 microg/ml for serotype 14. More than 90% of all subjects had a post-third dose titer of > or =0.15 microg/ml for all serotypes, and the percentage of infants with a post-third dose titer of > or =1.0 microg/ml ranged from 51% for type 9V to 89% for type 14. After the PNCRM7 booster dose, the GMCs of all seven serotypes increased significantly over both post-Dose 3 and pre-Dose 4 antibody levels. In the primary series there were no significant differences in GMCs of pneumococcal antibodies between the subjects given PN-CRM7 alone or concurrently with hepatitis B vaccine. At the toddler dose concurrent administration of PNCRM7 and DTaP and HbOC resulted in a near conventional threshold for statistical significance of a post-Dose 4 GMC for serotype 23F [alone 6.75 mirog/ml vs. concurrent 4.11 microg/ml (P = 0.057)] as well as significantly lower antibody GMCs for H. influenza polyribosylribitol phosphate, diphtheria toxoid, pertussis toxin and filamentous hemagglutinin. For all antigens there were no differences between study groups in defined antibody titers that are considered protective. CONCLUSION We conclude that PNCRM7 vaccine was safe and immunogenic. When this vaccine was administered concurrently at the booster dose with DTaP and HbOC vaccines, lower antibody titers were noted for some of the antigens when compared with the antibody response when PNCRM7 was given separately. Because the GMCs of the booster responses were all generally high and all subjects achieved similar percentages above predefined antibody titers, these differences are probably not clinically significant.

Determinants of release rate of tetanus vaccine from polyester microspheres

Controlled-release formulations based on poly(lactic) (PLA) and poly(lactic/glycolic) acid (PLGA) microspheres containing tetanus vaccine were designed. The polymers forming the microspheres were L-PLA of different molecular weights and DL-PLGA, 50:50. These microspheres were prepared by two solvent elimination procedures, both using a double emulsion, and were characterized for size, morphology, and toxoid release kinetics. The influence of formulation variables such as polymer type, vaccine composition, and vaccine/polymer ratio was also investigated. Both techniques yielded microspheres with similar size, morphology, and release properties. Microsphere size was dependent on the type of polymer and the presence of the surfactant L-α-phosphatidylcholine, which led to a reduction in microsphere size. On the other hand, the release kinetics of encapsulated protein were affected by the polymer properties (ratio lactic/glycolic acid and molecular weight) as well as by the vaccine composition, vaccine loading, and microsphere size. Moreover, for some formulations, a decrease in microsphere size occurred simultaneously, with an increase in porosity leading to an augmentation of release rate. The changes in the PLA molecular weight during in vitro release studies indicated that release profiles of tetanus toxoid from these microspheres were only marginally influenced by polymer degradation. A significant fraction of protein (between 15 and 35%) was initially released by diffusion through water-filled channels. In contrast, the decrease in the PLGA molecular weight over the first 10 days of incubation suggested that erosion of the polymer matrix substantially affects protein release from these microspheres. Among all formulations developed, two differing in microsphere size, polymer hydrophobicity, and release profile were selected for in vivo administration to mice. Administration of both formulations resulted in tetanus neutralizing antibody levels that were higher than those obtained after administration of the fluid toxoid.