Geographical differences in invasive pneumococcal disease rates and serotype frequency in young children.

The development of glycoconjugate vaccines for Streptococcus pneumoniae that are effective in very young children has renewed interest in identification of which among the more than 90 pneumococcal serotypes are most likely to cause invasive pneumococcal disease (IPD). Serotype distribution is thought to vary geographically, even between regions as socioeconomically similar as western Europe and North America. To explain these variations, we note the considerable variation that exists between reported rates of IPD in young children in the USA and west European countries. We postulate that this variation is attributable to different blood-culture rates and practices, and that mild IPD is probably underdiagnosed and under-reported in western Europe. On the basis of a comparison of serotype distributions between the two regions, we also postulate that those serotypes found at similar frequencies in both regions are virulent and rarely cause mild disease. As a result, reported distributions of IPD serotypes, especially when expressed as percentages, might be strongly skewed by the distribution of clinical presentations in a particular study population.

Safety and immunogenicity of four doses of Neisseria meningitidis group C vaccine conjugated to CRM197 in United States infants.

BACKGROUND: Following widespread use of conjugate pneumococcal vaccine, Neisseria meningitidis likely will become the leading cause of bacterial sepsis and meningitis in US children. This report describes the safety and immunogenicity in US children of four consecutive doses of a meningococcal group C vaccine conjugated to CRM197 via reductive amination (MnCC). METHODS: One hundred six healthy 2-month-old infants received MnCC at 2, 4 and 6 months of age in a randomized, controlled double blind study; children in the other treatment arm were given a 7-valent conjugate pneumococcal vaccine. Parents reenrolled 64 of these children at 12 to 15 months to receive a fourth dose of MnCC. Routine childhood vaccines, including DTP, were coadministered. Temperatures and symptoms were recorded for 3 days after each immunization. Serum enzyme-linked immunosorbent assay IgG and bactericidal antibodies were measured prevaccination and before and 1 month after Doses 3 and 4. RESULTS: Moderate to severe local reactions, defined as erythema or induration > or =2.4 cm or pain that interfered with limb movement was reported after 0 to 3.2% of MnCC injections, depending on the reaction and dose. Fever occurred in 23 to 37% of children, but the contribution of MnCC to the febrile reactions is unknown. Geometric mean concentrations of IgG antibody to group C meningococcal polysaccharide were 3.72 microg/ml after Dose 3 and 8.03 microg/ml after the booster. Geometric mean functional serum bactericidal antibody titers after Doses 3 and 4 were 1:463 and 1:2341, respectively. One hundred percent of children had a serum bactericidal antibody titer of > or =1:64 after three doses and > or = 1:128 after the booster. CONCLUSIONS: The MnCC vaccine had an acceptable safety profile and generated high titers of bactericidal antibody in immunized US infants and toddlers. It appears to be an attractive candidate vaccine for the prevention of serogroup C meningococcal disease in young children.

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.

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.

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.

Safety and immunogenicity of heptavalent pneumococcal vaccine conjugated to CRM197 in United States infants.

OBJECTIVE: To determine the safety and immunogenicity of heptavalent pneumococcal saccharide vaccine (serotypes 4, 6B, 9V, 14, 18C, 19F, 23F) individually conjugated to CRM197 (PNCRM7), administered at 2, 4, 6, and 12 to 15 months of age. DESIGN: Two hundred twelve healthy 2-month-old infants were equally randomized to receive four consecutive doses of PNCRM7 or an investigational meningococcal group C conjugate vaccine, which served as a control. Concomitantly administered routine vaccines were oral polio vaccine and combined diphtheria toxoid, tetanus toxoid, and whole cell pertussis vaccine/Haemophilus influenzae type b vaccine consisting of capsular oligosaccharides conjugated to CRM197 (DTP/HbOC) at 2, 4, and 6 months, and either measles-mumps-rubella vaccine or HbOC at 12 to 15 months. Active safety surveillance was conducted for 3 days after each dose. Antibody concentrations to each of the 7 pneumococcal serotypes were measured by enzyme-linked immunosorbent assay prevaccination, after doses two and three, prebooster, and postbooster. RESULTS: Significantly fewer children experienced local reactions at the PNCRM7 injection site than at the DTP/HbOC site. There was no increase in the incidence or severity of local reactions at the PNCRM7 site with increasing doses of vaccine. Mild to moderate postvaccination fever was common in both the PNCRM7 and control vaccine groups, however DTP/HbOC was administered concurrently. All 7 vaccine serotypes were immunogenic. The kinetics of the immune responses were serotype-specific. After three doses of PNCRM7, between 92% to 100% of children had >/=0.15 microg/mL of antibody, and 51% to 90% achieved a level of >/=1 microg/mL against specific serotypes. A booster dose of PNCRM7 resulted in a brisk anamnestic response to all 7 vaccine serotypes, demonstrating effective stimulation of T-cell memory by the primary series of vaccinations. CONCLUSION: Primary immunization followed by a booster dose of PNCRM7 seemed to be acceptably safe and resulted in significant rises in antibody to all 7 serotypes. Implications. Studies to assess vaccine efficacy of PNCRM7 for prevention of systemic disease, nasopharyngeal colonization, and acute otitis media are in progress. If PNCRM7 proves to be protective, there is the potential to prevent up to 85% of invasive pneumococcal disease occurring in US children.

Safety and immunogenicity of a purified F protein respiratory syncytial virus (PFP-2) vaccine in seropositive children with bronchopulmonary dysplasia.

Respiratory syncytial virus (RSV) causes serious respiratory illness in preterm children with bronchopulmonary dysplasia. In a prospective randomized placebo-controlled trial, 21 children received one dose of PFP-2 (purified fusion [F] protein) vaccine or influenza vaccine (placebo). Children were followed for adverse reactions and RSV illness over two respiratory seasons. Sera were obtained for determination of IgG titers to RSV F protein and neutralizing antibody titers before and 1, 6, and 12 months after vaccination. Adverse reactions were few. Four-fold F protein rises occurred in 9 of 10 PFP-2 and 0 of 11 placebo recipients. Six PFP-2 recipients had low prevaccination neutralizing antibody titers (< 1:450); all had 4-fold rises. By 12 months, F protein and neutralizing antibody titers in all 21 children were similar. RSV illness occurred in 6 of 11 placebo versus 1 of 10 PFP-2 recipients (P = .06); 1 placebo child required hospitalization. PFP-2 vaccine appears safe and immunogenic and may protect children with bronchopulmonary dysplasia against serious RSV disease on reinfection.

Glycoconjugate vaccines: future combinations.

There is a large and growing base of knowledge about the protective immune response to encapsulated bacterial pathogens. This information is a clear advantage to the development of glycoconjugate vaccines. It is well understood for such pathogens as Haemophilus b, pneumococcus, meningococcus and group b streptococcus that the induction of a functional anti-saccharide antibody response is likely to be protective. The most important question for glycoconjugate vaccines is the magnitude of the response required for protection. Even after extensive field trials with Haemophilus b vaccines, there is not a precise antibody correlate of immunity. In fact, cited values still rely on older studies with polysaccharide vaccine [11]. For that reason, vaccine such as the multivalent pneumococcal formulations will require field trials to measure their efficacy and hopefully determine the appropriate correlates of immunity. However, the addition of new serotypes into a multivalent pneumococcal formulation after efficacy trials are completed will probably have to be based on antibody correlates since it will not be possible to do efficacy studies on individual serotypes especially since they will have low prevalence. A similar dilemma may be faced with a vaccine for the group C meningococcus where the low disease incidence will make efficacy studies difficult. As was the case with mixing DTP and Hib vaccines, in the future combinations of effective antigens will continue to rely on comparative immunogenicity studies to ensure efficacy. It is clear that the immune system is capable of responding to a diversity of antigens simultaneously. However, it is also clear that vaccine components can interfere with each other and this interference is not necessarily predictable [12]. The ability to measure the stability of each of the components of a combined product reliably will become even more critical as the complexity of the mixtures increases.

Safety and immunogenicity of the PFP vaccine against respiratory syncytial virus (RSV): the western blot assay aids in distinguishing immune responses of the PFP vaccine from RSV infection.

PFP-1 vaccine was evaluated in a randomized, controlled study in 47 RSV seropositive children. Trivalent inactivated influenza virus (TIV) vaccine was the control. Vaccine reactions were monitored, and bloods were obtained before vaccination, 4 weeks after vaccination, and at the end of the RSV season. Respiratory illnesses were evaluated during the outbreak. Neutralizing antibody (Nt Ab) assay to RSV, IgG ELISA to RSV proteins and a Western blot assay were performed. Acute reactions with the PFP vaccine were mild. An early RSV outbreak resulted in infection of 44.4% of the TIV recipients shortly after vaccination. In the PFP vaccine groups, the Nt Ab and ELISA assays did not distinguish between Ab rises due to natural infection versus vaccine; however, the Western blot assay characterized the post-vaccine rises. Two major Western blot profiles were produced: an infection profile (antibodies that recognized the F and G surface glycoproteins and internal proteins) and a vaccine profile (antibodies that recognized only the surface glycoproteins). The PFP vaccinees who were not infected with RSV developed ELISA and Nt Ab responses to the surface glycoproteins that were similar to the TIV vaccines with natural RSV infection. None of the children developed vaccine-enhanced disease. Thus, the PFP-1 vaccine was safe and immunogenic in RSV seropositive children even when vaccine was administered during a RSV outbreak, and the Western blot assay was useful in distinguishing Ab rises caused by RSV infection versus PFP vaccine.

Combination vaccines for diphtheria, tetanus, pertussis, and Haemophilus influenzae type b.

The ability to combine the standard DTP and Haemophilus b conjugate vaccine considerably simplifies the childhood immunization schedule and process. In addition to reducing the number of immunizations by half, the combination product reduces administrative aspects associated with vaccination including tracking. Simplification of the immunization process should have a positive impact on the vaccine delivery and utilization. Perhaps more importantly, an ability to create combination vaccines will be critical for inclusion of new antigens appropriate for infant vaccines. The combination of DTP and HbOC reduces the number of immunizations routinely given at 2, 4, and 6 months of age by half. Since it is unlikely that parents or pediatricians will accept more than two shots per visit, this reduction is critical. As new vaccines are licensed for such important childhood pathogens as Streptococcus pneumoniae and respiratory syncytial virus, designing stable combination products will become even more critical. Having stated that, we must also not lose site of the fact that combination products must meet the criteria for stability, safety, and efficacy comparable to the separately delivered products. These considerations are not trivial. In the development of Tetramune (DTP-HbOC), stability of the product and consistency of the immune response were critical design parameters for both the preclinical and clinical research. Likewise, the experience with other DTP-Haemophilus b combinations has shown that simple mixing of products prior to injection can reduce the immune response in ways that are not necessarily predictable. In contrast, the response to each of the components of Tetramune was in fact higher than when the vaccines were given separately. This increased response to all of the antigens was not anticipated based on the vaccine composition and points to the need for not only physical characterization of new combinations, but also clinical testing of final combined products before they are introduced for routine use.

The immunogenicity of Haemophilus influenzae type b conjugate (HbOC) vaccine in human immunodeficiency virus-infected and uninfected infants.

Enzyme-linked immunosorbent assay polyribosyl ribitol phosphate (PRP) antibody responses to Haemophilus influenzae type b conjugate vaccine (HbOC) given at 2, 4 and 6 months of age were retrospectively compared in 23 human immunodeficiency virus (HIV) and 24 non-HIV-infected infants. HIV-infected infants were divided into those who were P1 (asymptomatic) or P2 (symptomatic) by 1 year of age. The P2 group was further divided into P2A (mildly symptomatic) and > P2A (rapidly symptomatic) by 1 year of age. The post-third HbOC dose geometric mean antibody titer to PRP was significantly lower in 12 P2 infants (0.43 microgram/ml) than either the 11 P1 infants (5.03 micrograms/ml, P < 0.05) or the 24 non-HIV infected infants (3.43 micrograms/ml, P < 0.05). Within the P2 group, the geometric mean antibody titer to PRP was significantly higher in 5 P2A infants (1.63 micrograms/ml) compared with 7 infants who were > P2A (0.17 microgram/ml, P < 0.05). After the third HbOC dose, PRP antibody titers were > or = 1.0 micrograms/ml for 4 of 12 P2 compared with 9 of 11 P1 infants (P < 0.05). Within the P2 group, PRP antibody titers were > 1.0 micrograms/ml for 4 of 5 P2A compared to 0 of 7 infants who were > P2A (P < 0.05). HIV-infected infants with PRP antibody titers > or = 1.0 micrograms/ml after the third HbOC dose had significantly higher mean CD4 counts (2842 cells/mm3) at the time of the third HbOC dose than those with lower PRP titers (1655 cells/mm3) (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Safety and immunogenicity of a subunit respiratory syncytial virus vaccine in children 24 to 48 months old.

A subunit vaccine for respiratory syncytial virus (RSV) consisting of purified fusion glycoprotein (designated PFP-1) was tested in children 24 to 48 months old. Two doses of 20 micrograms (n = 13) and 50 micrograms (n = 10) were compared with a saline (n = 24) placebo control group. Local and systemic reactions, reported within 96 hours postvaccination, were mild, transient, and did not differ significantly from the control cohort. Long term follow-up through at least one, and in some cases two, RSV seasons showed no serious RSV illness in vaccinees at any time. There was, therefore, no evidence of disease enhancement postvaccination. In the 20-micrograms cohort, 92% responded to vaccination by a 4-fold increase in enzyme-linked immunosorbent titer to the F glycoprotein and 42% had a 4-fold or greater rise in neutralizing titer to the A2 virus. In the 50-micrograms cohort 100% responded by enzyme-linked immunosorbent to the F glycoprotein and 70% responded by A2-neutralizing titers. The neutralizing titers in the vaccinated cohorts were similar to those seen previously in adults. These data show the ability of the subunit vaccine to boost existing immunity and to prime for a response to natural virus exposure in children who were seronegative at the time of vaccination.

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.

Expression of the G glycoprotein gene of human respiratory syncytial virus in Salmonella typhimurium.

The attachment protein, G, of human respiratory syncytial virus (RSV) is an M(r) 84K to 90K species which has a high content of N-linked and O-linked carbohydrates. The unglycosylated form of this protein was expressed by inserting a full-length cDNA copy of the mRNA from the A2 strain of RSV into a prokaryotic expression vector under the control of the lambda PL promoter. Salmonella typhimurium cells transformed with the G-containing plasmid synthesized a protein of M(r) 40,000 that specifically reacted with polyclonal and two neutralizing monoclonal antibodies raised against the native RSV G glycoprotein. Recombinant G protein was purified by immunoaffinity chromatography using a neutralizing monoclonal antibody. Cotton rats immunized with the recombinant G protein produced serum antibodies to the G glycoprotein that neutralized RSV in vitro. The study demonstrates that the G protein of RSV can be expressed in bacteria and that at least one neutralizing epitope is not structurally dependent on carbohydrates.

Lack of detectable enhanced pulmonary histopathology in cotton rats immunized with purified F glycoprotein of respiratory syncytial virus (RSV) when challenged at 3-6 months after immunization.

The cotton rat model has been used to evaluate the potential for immunogens to induce respiratory syncytial virus (RSV)-enhanced pulmonary histopathology. A recent study evaluated purified F protein in this model when animals were challenged intranasally with RSV 3 or 6 months after immunization. The authors concluded that the purified F protein was associated with the same level of histopathological changes as observed with the positive control, a formalin-inactivated RSV immunogen. Three pathologists have independently evaluated the lung sections from the animals of this study and the results are reported in this article. In contrast to the previously published data, we have found that F protein was associated with a substantially milder and qualitatively different response to that observed with the formalin-inactivated RSV vaccine. We concluded that the minimal histological changes observed and lack of clinical disease make it very difficult to assess the issue of enhanced pulmonary RSV disease with the cotton rat model.