Defining Polysaccharide-Specific Antibody Targets against Vibrio cholerae O139 in Humans following O139 Cholera and following Vaccination with a Commercial Bivalent Oral Cholera Vaccine, and Evaluation of Conjugate Vaccines Targeting O139

Cholera caused by Vibrio cholerae O139 could reemerge, and proactive development of an effective O139 vaccine would be prudent. To define immunoreactive and potentially immunogenic carbohydrate targets of Vibrio cholerae O139, we assessed immunoreactivities of various O-specific polysaccharide (OSP)-related saccharides with plasma from humans hospitalized with cholera caused by O139, comparing responses to those induced in recipients of a commercial oral whole-cell killed bivalent (O1 and O139) cholera vaccine (WC-O1/O139). We also assessed conjugate vaccines containing selected subsets of these saccharides for their ability to induce protective immunity using a mouse model of cholera. We found that patients with wild-type O139 cholera develop IgM, IgA, and IgG immune responses against O139 OSP and many of its fragments, but we were able to detect only a moderate IgM response to purified O139 OSP-core, and none to its fragments, in immunologically naive recipients of WC-O1/O139. We found that immunoreactivity of O139-specific polysaccharides with antibodies elicited by wild-type infection markedly increase when saccharides contain colitose and phosphate residues, that a synthetic terminal tetrasaccharide fragment of OSP is more immunoreactive and protectively immunogenic than complete OSP, that native OSP-core is a better protective immunogen than the synthetic OSP lacking core, and that functional vibriocidal activity of antibodies predicts in vivo protection in our model but depends on capsule thickness. Our results suggest that O139 OSP-specific responses are not prominent following vaccination with a currently available oral cholera vaccine in immunologically naive humans and that vaccines targeting V. cholerae O139 should be based on native OSP-core or terminal tetrasaccharide. IMPORTANCE Cholera is a severe dehydrating illness of humans caused by Vibrio cholerae serogroup O1 or O139. Protection against cholera is serogroup specific, and serogroup specificity is defined by O-specific polysaccharide (OSP). Little is known about immunity to O139 OSP. In this study, we used synthetic fragments of the O139 OSP to define immune responses to OSP in humans recovering from cholera caused by V. cholerae O139, compared these responses to those induced by the available O139 vaccine, and evaluated O139 fragments in next-generation conjugate vaccines. We found that the terminal tetrasaccharide of O139 is a primary immune target but that the currently available bivalent cholera vaccine poorly induces an anti-O139 OSP response in immunologically naive individuals.

Pneumococcal conjugate vaccine update

ACIP no longer recommends routine use of PCV13 in immunocompetent adults ≥ 65 years. Three simple statements summarize guidance on intervals to follow when administering both PCV13 and PPSV23.

Immunization update: This year's changes

The 9-valent formulation of HPV vaccine is now on the schedule, but don't delay starting or continuing the vaccine series just because HPV9 is not on hand. Give the 2 pneumococcal vaccines a year apart.

Estimating strain-specific and overall efficacy of polyvalent vaccines against recurrent pathogens from a cross-sectional study

Evaluating vaccine efficacy for protection against colonization with bacterial pathogens is an area of growing interest. Colonization of the nasopharynx is an asymptomatic carrier state responsible for person-to-person transmission. It differs from most clinical outcomes in that it is common, recurrent, and observed only in its prevalent state. To estimate rates of acquisition and clearance of colonization requires repeated active sampling of the same individuals over time, an expensive and invasive undertaking. Motivated by feasibility constraints in efficacy trials with colonization endpoints, investigators have been estimating vaccine efficacy from cross-sectional studies without principled methods. We present two examples of vaccine studies estimating vaccine efficacy from cross-sectional data on nasopharyngeal colonization by Streptococcus pneumoniae (pneumococcus). This study presents a framework for defining and estimating strain-specific and overall vaccine efficacy for susceptibility to acquisition of colonization (VE(acq)) when there is a large number of strains with mutual interactions and recurrent dynamics of colonization. We develop estimators based on one observation of the current status per study subject, evaluate their robustness, and re-analyze the two vaccine trials. Methodologically, the proposed estimators are closely related to case-control studies with prevalent cases, with appropriate consideration of the at-risk time in choosing the controls.

Licensure of a Haemophilus influenzae type b (Hib) vaccine (Hiberix) and updated recommendations for use of Hib vaccine

On August 19, 2009, the Food and Drug Administration (FDA) licensed Hiberix (GlaxoSmithKline Biologicals, Rixensart, Belgium), a Haemophilus influenzae type b (Hib) conjugate vaccine composed of H. influenzae type b capsular polysaccharide (polyribosyl-ribitol-phosphate [PRP]) conjugated to inactivated tetanus toxoid (PRP-T). Hiberix is licensed for use as the booster (final) dose of the Hib vaccine series for children aged 15 months through 4 years (before the 5th birthday) who have received previously the primary series of Hib vaccination (consisting of 2 or 3 doses, depending on the formulation). The Advisory Committee on Immunization Practices (ACIP) recommends Hib booster vaccination for children at ages 12 through 15 months; however, because of the recent shortage of Hib vaccines, many children have deferred the booster dose and therefore require catch-up vaccination. This report summarizes the indications for Hiberix use and provides guidance on Hib booster dose administration based on increasing vaccine supplies. Vaccination recommendations in this report update the previous advisory on Hib booster administration (June 26, 2009), which advised that children with deferred booster doses receive it at the next regularly scheduled visit. Vaccination providers are now recommended to begin recall of children in need of the booster dose when feasible and monovalent Hib vaccine supply in the office is adequate.

Pediatricians' adherence to pneumococcal conjugate vaccine shortage recommendations in 2 national shortages

OBJECTIVES

The goals were (1) to compare pediatricians' heptavalent pneumococcal conjugate vaccine shortage experience and adherence to shortage recommendations during 2 heptavalent pneumococcal conjugate vaccine shortages, (2) to assess factors associated with nonadherence to second shortage recommendations, and (3) to assess opinions about national immunization policy during vaccine shortages.

METHODS

We mailed surveys to all pediatrician immunization providers in the greater Cincinnati, Ohio, metropolitan area. We assessed heptavalent pneumococcal conjugate vaccine supply and immunization practices during the shortages and provider attitudes regarding immunization shortage policy.

RESULTS

The response rate was 61% (171 of 282 providers). Most pediatricians experienced heptavalent pneumococcal conjugate vaccine shortages (first shortage: 86%; second shortage: 84%). The rate of adherence to recommendations to defer the fourth heptavalent pneumococcal conjugate vaccine dose for healthy children was significantly higher during the second shortage, compared with the first shortage (first shortage: 62%; second shortage: 89%). Adherence to recommendations to administer the fourth dose to high-risk children remained unchanged (first shortage: 43%; second shortage: 45%). Controlling for other factors, pediatricians who reported a severe second shortage had greater odds of not fully vaccinating high-risk children, compared with those who reported no shortage. Contrary to recommendations, many pediatricians did not maintain tracking systems during the heptavalent pneumococcal conjugate vaccine shortages (first shortage: 37%; second shortage: 46%). Most pediatricians (91%) thought that national vaccine shortage recommendations were needed to protect them from liability.

CONCLUSIONS

The rate of adherence to recommendations to defer heptavalent pneumococcal conjugate vaccine doses for healthy children increased significantly from the first shortage to the second shortage. The nonadherent practice of deferring the fourth dose for high-risk children was associated with more severe shortages and, potentially, an inability to vaccinate.

Impact of pneumococcal conjugate vaccine on the prevention of invasive pneumococcal diseases

OBJECTIVES

To evaluate the impact of heptavalent pneumococcal conjugate vaccine in invasive pneumococcal diseases in the United States, and to analyze the potential impact of this vaccine in Brazil.

SOURCES OF DATA

MEDLINE, LILACS, Cochrane Database Reviews, as well as the websites of the Centers for Disease Control and Prevention (CDC), Brazilian Ministry of Health and Centro de Vigilância Epidemiológica do Estado de São Paulo from January 2000 to January 2006. Articles retrieved with the keywords Streptococcus pneumoniae, pneumococcal diseases, conjugate vaccine, antimicrobial resistance and meningitis were reviewed.

SUMMARY OF THE FINDINGS

The introduction of heptavalent pneumococcal conjugate vaccine caused a dramatic reduction in the incidence of invasive pneumococcal diseases in American children, reduced antibiotic use and the number of medical visits due to otitis media and pneumonia by children. The incidence of invasive pneumococcal diseases caused by resistant strains declined in immunized children, adults and elderly individuals. In Brazil, the mortality rate of pneumococcal meningitis is very high and the resistance to antibiotics has increased over the last 5 years.

CONCLUSIONS

Heptavalent pneumococcal conjugate vaccine can benefit not only children, but the entire community and should be included in the Brazilian routine immunization schedule.

Pneumococcal conjugate vaccination in children with recurrent acute otitis media: a therapeutic alternative?

BACKGROUND

Based on two clinical trials in healthy infants the American Academy of Pediatrics (AAP) advices immunization with a 7-valent pneumococcal conjugate vaccine in children with recurrent acute otitis media (AOM).

OBJECTIVE

To study the efficacy of a 7-valent pneumococcal conjugate vaccine on acute otitis media recurrences, its immunogenicity and impact on nasopharyngeal Streptococcus pneumoniae carriage in children with a history of frequent acute otitis media.

METHODS

In this double-blind, randomized study, 74 Belgian children, aged 1-7 years, with at least 2 clinically diagnosed episodes of acute otitis media in the previous year were enrolled. Children were immunized with either a 7-valent pneumococcal conjugate vaccine followed by a 23-valent pneumococcal polysaccharide booster or a control hepatitis A vaccine. Total follow-up was 26 months.

RESULTS

Despite adequate serum IgG responses to all conjugate vaccine pneumococcal serotypes, no reduction of acute otitis media episodes was observed in the pneumococcal vaccine group as compared to the control group (rate ratio: 1.16; 95% CI: 0.69-1.96). Overall nasopharyngeal pneumococcal carriage remained stable. However, a transient shift from conjugate vaccine related S. pneumoniae serogroups to non-vaccine related serogroups was noted following conjugate vaccination.

CONCLUSION

Clinically no protective effect of pneumococcal conjugate vaccination on acute otitis media recurrences was found in children with a history of frequent AOM.

NMR assays for carbohydrate-based vaccines

Antibodies against the cell surface carbohydrates of many microbial pathogens protect against infection. This was initially exploited by the development of purified polysaccharide vaccines, but glycoconjugate vaccines, in which the cell surface carbohydrate of a microbial pathogen is covalently attached to an appropriate carrier protein, are proving the most effective means to generate this protective immunity. Carbohydrate-based vaccines against Haemophilus influenzae Type b, Neisseria meningitidis, Streptococcus pneumoniae and Salmonella enterica serotype Typhi (S. Typhi) are already licensed, and many similar products are in various stages of development. For many of these vaccines, biological assays are not available or are inappropriate and NMR spectroscopy is proving a valuable tool for the characterisation and quality control of existing and novel products. This review highlights some of the areas in which NMR spectroscopy is currently used, and where further developments may be expected.

Vaccines based on the cell surface carbohydrates of pathogenic bacteria

Glycoconjugate vaccines, in which a cell surface carbohydrate from a micro-organism is covalently attached to an appropriate carrier protein are proving to be the most effective means to generate protective immune responses to prevent a wide range of diseases. The technology appears to be generic and applicable to a wide range of pathogens, as long as antibodies against surface carbohydrates help protect against infection. Three such vaccines, against Haemophilus influenzae type b, Neisseria meningitidis Group C and seven serotypes of Streptococcus pneumoniae, have already been licensed and many others are in development. This article discusses the rationale for the development and use of glycoconjugate vaccines, the mechanisms by which they elicit T cell-dependent immune responses and the implications of this for vaccine development, the role of physicochemical methods in the characterisation and quality control of these vaccines, and the novel products which are under development.

Pneumococcal conjugate vaccines—a European perspective

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and acute otitis media in children and adults worldwide. In the age group of < 2 years the incidence of invasive pneumococcal disease ranges from approximately 14 cases per 100,000 in Germany and the Netherlands and more than 90 per 100,000 children in Spain. The vulnerability of children to S. pneumoniae can also be demonstrated by the high rate of sequelae (> 20% in Germany) and the high mortality (7.5%) in pneumococcal meningitis. Furthermore, antibiotic resistance of S. pneumoniae is increasing in Europe, particularly in France, Spain, and Eastern European countries, whereas Germany and Northern Europe are only marginally affected. A 7-valent pneumococcal conjugate vaccine (7vPCV) that was shown to be highly efficacious in preventing invasive pneumococcal disease in infants in the USA was licensed in Europe in 2001. It is expected that broad usage of the vaccine would reduce the incidence of invasive pneumococcal disease and the levels of pneumococcal resistance significantly. Important questions have been raised regarding the effectiveness of this vaccine in high-risk populations, serotype replacement, the efficacy of this vaccine in otitis media, and the co-administration of the new vaccine with other standard childhood vaccines used in various European countries. France and Spain currently have the most-wide ranging guidelines recommending pneumococcal vaccination for children. Overall, the development of pneumococcal conjugate vaccines is a significant step in the control of pneumococcal disease in children in Europe. Further progress in pneumococcal vaccine development can be expected from conjugate vaccines including more than seven serotypes (9-valent, 11-valent).

Pediatricians' Self-reported Clinical Practices and Adherence to National Immunization Guidelines After the Introduction of Pneumococcal Conjugate Vaccine

BACKGROUND

Little is known about whether pneumococcal conjugate vaccine (PCV) has altered pediatricians' practices regarding well-child and acute care.

OBJECTIVES

To (1) describe whether PCV caused pediatricians to move other routine infant vaccines and/or add routine visits; (2) characterize adherence to national immunization recommendations; and (3) determine whether PCV altered pediatricians' planned clinical approach to well-appearing febrile infants.

DESIGN AND METHODS

One year after PCV was added to the pediatric immunization schedule, we mailed a 23-item survey to 691 randomly selected pediatricians in Massachusetts. The adjusted response rate was 77%.

RESULTS

After PCV introduction, 39% of pediatricians moved other routine infant vaccines to different visits and 15% added routine visits to the infant schedule. The self-reported immunization schedules of 36% were nonadherent to national immunization guidelines for at least 1 vaccine. Nonadherence rates were significantly higher among pediatricians who had been in practice longer, moved another vaccine because of PCV introduction, and/or offered to give shots later when multiple injections were due. For a hypothetical febrile 8-month-old girl who had received 3 doses of PCV, pediatricians reported they were significantly less likely to (1) perform both blood and urine testing and (2) prescribe antibiotics than in the pre-PCV era.

CONCLUSIONS

The introduction of PCV may have had unintended effects on pediatric primary care, including decreased adherence to national recommendations for the timing of immunizations and decreased urine testing for well-appearing febrile infants. Special efforts may be warranted to ensure that pediatricians remain current with changing recommendations.

Scientific challenges for the quality control and production of group C meningococcal conjugate vaccines

Recommendations (formerly known as requirements) for meningococcal polysaccharide vaccines were adopted by the World Health Organisation (WHO) Expert Committee on Biological Standardisation in 1976 and amended in 1978 and 1981. In clinical studies, these vaccines have been shown to have efficacy of at least 90% and have proved to be highly effective in vaccination programmes. Nevertheless, their inability to elicit protective responses in young infants or to induce good immunological memory has prevented their implementation in national infant immunisation schedules. Following the successful introduction of the Haemophilus influenzae type b conjugate (Hib) vaccines, considerable progress has been made in the development of similar conjugate vaccines based on meningococcal group C capsular polysaccharide. Controlled clinical trials have demonstrated that they induce protective levels of antibodies to group C polysaccharide in all age groups and, as T-cell dependent antigens, induce immunological memory and affinity maturation of anti-capsular antibodies. Such vaccines have been shown to offer protective immunity following the introduction of group C conjugates in the UK. The World Health Organisation has produced recommendations for the production and control of these new vaccines.

WHO Expert Committee on Biological Standardization

This report presents the recommendations of a WHO Expert Committee commissioned to coordinate activities leading to the adoption of international requirements for the production and control of vaccines and other biologicals and the establishment of international biological reference materials. The report starts with a discussion of general issues brought to the Committee's attention and provides information on the status and development of reference materials for various antibodies, antigens, blood products and related substances, cytokines, growth factors, and endocrinological substances. The second part of the report, of particular relevance to manufacturers and national regulatory authorities, contains recommendations for the production and quality control of meningococcal group C conjugate vaccines, guidelines for regulatory expectations for clinical evaluation of vaccines, guidelines for the production and quality control of inactivated oral cholera vaccines and guidelines on viral inactivation and removal procedures intended to assure the viral safety of human blood plasma products.

Heptavalent pneumococcal vaccine conjugated to outer membrane protein of Neisseria meningitidis serogroup b and nasopharyngeal carriage of Streptococcus pneumoniae in infants

BACKGROUND

Streptococcus pneumoniae (Sp) is an important bacterial pathogen in children. Nasopharyngeal (NP) colonization of S. pneumoniae is necessary for person-to-person transmission and often precedes invasive disease.

METHODS

NP carriage of Sp was studied in 49 infants following administration of a heptavalent pneumococcal conjugate vaccine (PCV) conjugated to the outer membrane protein of serogroup b Neisseria meningitidis (vaccine serotypes: 4, 6B, 9V, 14, 18C, 19F, 23F). The vaccine was administered at 2, 4, 6, and 12 months of age and carriage rates were compared to a concurrent group of 32 infants not given PCV and evaluated over the first 15 months of life.

RESULTS

Overall, Sp was isolated in 86/367 (23%) of NP cultures and 49% of infants. Serotype 23F was significantly less prevalent in the PCV group (1.9%) than the control group (16.1%) (P<0.05). Analysis of the proportion of children with prevalent carriage or acquisition of carriage did not differ between groups when evaluated by age or serotype. We noted, however, decreased acquisition and carriage in the vaccine group 1 month following the 12 month dose of PCV for vaccine serotypes (76 and 52% reduction, respectively), but this did not reach statistical significance (P=0.3). Adjustment for age, daycare and antibiotic use by multivariate modeling revealed no difference in carriage of vaccine containing serotypes or non-vaccine serotypes between groups.

CONCLUSION

We did not show a significant effect of this heptavalent PCV on NP carriage. Further study of this issue, including a larger population size, is needed.

Vaccines for the prevention of meningococcal disease in children

Neisseria meningitidis is one of the most feared infections in pediatrics as the result of its rapid progression, high fatality rate, and frequent occurrence of sequelae. The 5 major meningococcal serogroups associated with disease are A, B, C, Y, and W-135. Currently available polysaccharide vaccines are effective in preventing disease caused by serogroups A, C, Y, and W-135 in older children and adults but do not elicit good long-term protection in young children. Vaccines that protect against serogroup B disease are still in development. As with the Haemophilus influenzae type b and pneumococcal polysaccharide vaccines, conjugation of the polysaccharide vaccine to a protein carrier dramatically changes vaccine characteristics, with resulting efficacy in infants. New meningococcal conjugate vaccines against serogroups A, C, Y, and W-135 are being developed. A serogroup C conjugate vaccine has been introduced successfully into the routine childhood schedule in the United Kingdom. New meningococcal conjugate vaccines are likely to have a dramatic effect on the burden of meningococcal disease within the next decade.

Pneumococcal conjugate vaccine for young children

Streptococcus pneumoniae causes approximately 3,300 cases of meningitis, 100,000 to 135,000 cases of pneumonia requiring hospitalization and 6 million cases of otitis media annually in the United States. Pneumococcal conjugate vaccine, approved in 2000 for use in the United States, was designed to cover the seven serotypes that account for about 80 percent of invasive infections in children younger than six years. This vaccine demonstrated 100 percent efficacy against invasive pneumococcal disease in the primary analysis of a large randomized, double-blind, controlled trial. In the follow-up analysis, performed eight months after the trial ended, efficacy against invasive disease was found to be 94 percent for the included serotypes. When initiated during infancy, the four-dose vaccination schedule is set at two, four, six and 12 to 15 months of age. The American Academy of Family Physicians recommends routine vaccination of infants, catch-up vaccination of children younger than 24 months and catch-up vaccination of children 24 to 59 months of age with high-risk medical conditions such as sickle cell disease and congenital heart disease.

WHO Expert Committee on Biological Standardization: highlights of the 50th meeting, October 1999

Biological medicines, which include vaccines, blood products and biological therapeutics, have historically played a dominant role in improving world health and are expected to make an increasingly important contribution to public health in the 21st century. Recent scientific and biotechnological developments have opened the way to novel products, new production methods and to highly sensitive assay procedures. However, the nature of biologicals, and especially new vaccines, blood products and therapeutics, raises particular questions regarding their standardization and quality control. These relate both to efficacy and to safety not only for the individual recipient but also for the population at large. Such advances highlight the complex issues surrounding standardization and control of biologicals, issues that need to be addressed on an international level.

An NMR spectroscopic identity test for the control of the capsular polysaccharide from Haemophilus influenzae type b

We describe the use of Nuclear Magnetic Resonance (NMR) spectroscopy to control the identity of purified bulk capsular polysaccharide [called poly(ribosylribitolphosphate) or PRP] from Haemophilus influenzae type b (Hib), and derivatised forms, used in the production of Hib polysaccharide-protein conjugate vaccines. We describe the approaches we have developed to validate this test.

Use of animal testing for evaluating glycoconjugate vaccine immunogenicity

Most animal species respond with high antibody levels to polysaccharide antigens after they have been covalently linked to a protein carrier, converting a T-cell independent to a T-cell dependent antigen. This chemical modification has enabled the development of glycoconjugate vaccines for Haemophilus influenzae type b, Neisseria meningitidis, and multivalent Streptococcus pneumoniae. This new generation of vaccines can be well characterized physically and chemically to ensure consistent vaccine manufacture. Such analytical tests provide an alternative to animal models for Quality Control Laboratories; biological models can be difficult and costly to develop and use on a routine basis. If animal tests are used, they need to be refined, defined, and validated for their intended purpose.

New methods for the characterisation of biopharmaceuticals: conjugate vaccines against Haemophilus influenzae type b

Modern physicochemical methods allow biological pharmaceuticals, particularly those arising from recombinant DNA technology, to be characterised with a degree of precision not previously possible. These techniques, which tell us what a material is (rather than what it does) provide an approach complementary to traditional bioassays for the control of biological pharmaceuticals. As we come to understand the mechanisms by which structural variation modulates the various biological activities of a product, structure-based assays will be able to replace biological identity and potency assays, although replacement of safety tests to find trace impurities (such as endotoxin) may be more difficult.

Serological assays as alternatives to the Ph Eur challenge test for batch release of tetanus vaccines for human use

According to the European Pharmacopoeia (Ph Eur) monograph on Tetanus Vaccine (adsorbed) (1997: 0452), assessment of potency is based on a challenge test in guinea pigs or mice. The end-point is taken as paralysis or death. The test requires a large number of animals and causes severe distress. The aim of the present study was to refine the test, and reduce the number of animals needed, for batch release purposes. Serological assays having the potential of being internationally accepted, have been compared with Ph Eur assays. The study included five tetanus vaccines of various combinations and produced by different manufacturers. The results indicated an excellent correlation between enzyme-linked immunosorbent assay (ELISA) and the challenge test (about 93% predictive value), as well as between the toxin binding inhibition (ToBI) test and the challenge test (about 95% predictive value) and between ELISA and the ToBI test (r = 0.92). Antitoxin concentrations determined by ELISA and ToBI were generally in the same range. An overall good correlation was also seen for serum pools of the guinea pigs injected with equal vaccine doses, between toxin neutralisation test in mice (TNT) and ELISA (r = 0.93) as well as between TNT and ToBI (r = 0.97). The ultimate goal of this project was to determine whether serological assays can be used for testing combined vaccines, particularly for tetanus and diphtheria components, using sera from the same animals.

[Level of bacterial endotoxins in Haemophilus influenzae type b vaccines conjugated with toxoids (td, Di)]

Quantitative evaluation of bacterial endotoxin was performed in the following vaccines: Act-Hib, Hiberix, Hib-Titer. The aim of this study was to assess the accuracy and precision of chromogenic LAL test with S-2423 substrate for this particular biopreparations and after that to determine the amounts of endotoxin as a factor of vaccine safety. Because of the lack of information concerning the presence of endotoxin in Act-Hib vaccine, we also tried to establish the limits for the presence of endotoxin in this type of vaccine. The estimated level of endotoxin was as follows: 110 EU/ml in Act-Hib, 1.64 EU/ml in Hiberix and 2.4 EU/ml in Hib-Titer. The results of this study showed that the amounts of endotoxin was dependent on the molecular size of polysaccharide PRP and on the presence of protein component. The limit of endotoxin presence in Act-Hib vaccine recommended by us is max. 150 EU/ml.

Standardization may suffice for licensure of conjugate vaccines

Standardization schemes devised by Control Agencies have followed clinical trials of experimental vaccines. The wealth of information about the pathogenesis of and immunity to bacteria, whose surface polysaccharides are protective antigens, now permits standardization to predict the efficacy of polysaccharide-based vaccines. There has been tacit acceptance of this notion with the licensure of groups Y and W135 meningococcal vaccines and of many of the pneumococcal types whose frequency in patients was too low for statistical significance to be assigned for their clinical efficacy. In fact, this was also the case for licensure of polio virus type 2 vaccine. We can reliably measure the level of anti-polysaccharide antibodies for meningococci, pneumococci, GBS and the Vi of S. typhi. Haemophilus type b conjugates have been reliably standardized by physico-chemical assays. New conjugates, therefore, may be licensed by data provided by standardization without awaiting the results of costly and time-consuming efficacy trials. Adoption of this scientifically-based approach to licensure will hasten the implementation of new and more effective vaccines.

Assignment of weight-based antibody units to a human antipneumococcal standard reference serum, lot 89-S

A human reference serum pool, lot 89-S, has been developed for use in quantitating concentrations of antibody to Streptococcus pneumoniae. Weight-based units have been assigned to antibodies to 11 pneumococcal polysaccharide (PnPs) serotypes (1, 3, 4, 5, 6B, 7F, 9V, 14, 18C, 19F, and 23F) by using enzyme-linked immunosorbent assay methodology and a human standard reference serum, USNRP IS 1644. The experimentally derived assignments for anti-PnPs antibodies of the immunoglobulin G (IgG), IgM, and IgA isotypes in lot 89-S correlate well to the separately determined immunoglobulin assignment. These assignments for this antipneumococcal standard serum were used to quantitate IgG, IgM, and IgA isotype levels and the total immunoglobulin level in pediatric samples from a pneumococcal conjugate vaccine trial. The data indicate that these assignments may be used to assess levels of antibody to PnPs serotypes in human serum.

Safety and immunogenicity of a combined diphtheria, tetanus, pertussis and Haemophilus influenzae type b vaccine in young infants

OBJECTIVE

To study the safety and immunogenicity of a combined diphtheria-tetanus-pertussis (DTP)-Haemophilus influenzae type b (HbOC) vaccine (TETRAMUNE) in infants as young as 2 months of age as compared to separate administration of DTP and HbOC.

METHODS

Two-month-old infants were randomized to receive three doses 2 months apart of either DTP-HbOC as a single 0.5-mL injection or to receive 0.5 mL of DTP and HbOC concurrently in separate legs. Local and systemic adverse reactions were monitored within 72 hours of each immunization, and immunogenicity of each of the four vaccine components was measured.

RESULTS

The incidence of both local and systemic adverse events following the tetravalent vaccine was similar to the incidence following separate vaccine administration. After three doses of vaccine, the response to each of the vaccine components was higher in the combined vaccine when compared to separate administration. In the case of the Haemophilus influenzae type b component, this enhancement was also seen after two doses. The response to the combined vaccine was consistent among the three lots tested as was the enhancement over separate administration.

CONCLUSIONS

The DTP-HbOC vaccine was safe and immunogenic in young infants and was generally more immunogenic than separate vaccination with DTP and HbOC. The use of such a combined vaccine reduces the number of injections given to young infants by half and is an important step toward improving vaccine delivery.