Prospects for pneumococcal vaccination in African children

The immunogenicity and impact on nasopharyngeal carriage of fewer doses of conjugate pneumococcal vaccine immunization schedule

The immunogenicity and impact on carriage of fewer doses of pneumococcal conjugate vaccine (PCV7) followed by booster with pneumococcal polysaccharide vaccine (PPV) were investigated. 684 infants were assigned randomly to one of the three groups that received one (A), two (B) or three (C) doses of PCV7 between 2 and 4 months of age, plus PPV at 10 months. Following primary vaccination protective antibody titers of >0.35 μg/ml against the PCV7 serotypes combined increased significantly with the number of PCV7 doses, 44% vs. 77% vs. 94% (p<0.001), and correlated positively with the opsonophagocytic indices, but negatively with nasopharyngeal carriage of pneumococcus. The differences in antibody responses and pneumococcal carriage between the groups diminished following booster with PPV, implying that administration of one or two doses of PCV7, with a booster dose of PPV might lower the cost of protection against IPD in young children in resource poor countries.

Invasive disease and paediatric carriage of Streptococcus pneumoniae in Ghana

This study was carried out primarily to evaluate the public health burden related to Streptococcus pneumoniae in Ghana and to provide related preliminary molecular epidemiological data on the organism. Invasive and nasopharyngeal specimens were screened for S. pneumoniae, and isolates were subjected to serotyping, multilocus sequence typing (MLST) and antibiotic susceptibility testing. Overall, the prevalence of S. pneumoniae in cerebrospinal fluid (CSF) was 1.7%, in blood was 0.2%, and in nasopharyngeal specimens was 15.3%. The prevalence of multiple drug resistance among the isolates was 48.6%, while the percentage resistance to various drugs was in the range of 11.1-84.0%. Serotyping of the S. pneumoniae isolates showed 7 different serotypes (3, 6B, 9, 10, 14, 16 and 23F). The extent of coverage of serotypes by the 7-valent pneumococcal conjugate vaccine was 57.1%, for the 10-valent vaccine was 57.1%, and for the 13-valent vaccine was 71.4%. MLST of 7 housekeeping genes of the organism showed a high level of genetic diversity among the isolates. S. pneumoniae appears to be an important organism in invasive infections in Ghana, being the most prevalent organism in CSF in this study. The high multiple drug resistance of the organism observed heightens the public health burden, which may be controlled by pneumococcal conjugate vaccines to a large extent.

Herd immunity and pneumococcal conjugate vaccine: A quantitative model

Invasive pneumococcal disease in older children and adults declined markedly after introduction in 2000 of the pneumococcal conjugate vaccine for young children. An empirical quantitative model was developed to estimate the herd (indirect) effects on the incidence of invasive disease among persons >or=5 years of age induced by vaccination of young children with 1, 2, or >or=3 doses of the pneumococcal conjugate vaccine, Prevnar (PCV7), containing serotypes 4, 6B, 9V, 14, 18C, 19F and 23F. From 1994 to 2003, cases of invasive pneumococcal disease were prospectively identified in Georgia Health District-3 (eight metropolitan Atlanta counties) by Active Bacterial Core surveillance (ABCs). From 2000 to 2003, vaccine coverage levels of PCV7 for children aged 19-35 months in Fulton and DeKalb counties (of Atlanta) were estimated from the National Immunization Survey (NIS). Based on incidence data and the estimated average number of doses received by 15 months of age, a Poisson regression model was fit, describing the trend in invasive pneumococcal disease in groups not targeted for vaccination (i.e., adults and older children) before and after the introduction of PCV7. Highly significant declines in all the serotypes contained in PCV7 in all unvaccinated populations (5-19, 20-39, 40-64, and >64 years) from 2000 to 2003 were found under the model. No significant change in incidence was seen from 1994 to 1999, indicating rates were stable prior to vaccine introduction. Among unvaccinated persons 5+ years of age, the modeled incidence of disease caused by PCV7 serotypes as a group dropped 38.4%, 62.0%, and 76.6% for 1, 2, and 3 doses, respectively, received on average by the population of children by the time they are 15 months of age. Incidence of serotypes 14 and 23F had consistent significant declines in all unvaccinated age groups. In contrast, the herd immunity effects on vaccine-related serotype 6A incidence were inconsistent. Increasing trends of non-vaccine serotypes, in particular 19A, were noted in most unvaccinated age groups, but these increases were substantially smaller than the concurrent decreases among the vaccine serotypes. Also, the model estimated PCV7 to have a greater (p=0.014) indirect impact on the incidence of invasive pneumococcal disease caused by all vaccine serotypes among African-Americans of all ages than for whites. Thus, conjugate vaccines may be able to induce herd effects even in situations where vaccine coverage is far from complete or with schedules using fewer than 3 or 4 doses. Because the model was based on incidence rates and PCV7 coverage in Atlanta, our findings should be validated in other geographic areas.

Invasive pneumococcal disease in children<5 years of age in rural Mozambique

OBJECTIVES

To estimate the incidence and epidemiological characteristics of invasive pneumococcal disease (IPD) in children<5 years of age living in a rural area of southern Mozambique.

METHODS

As part of the clinical management of children admitted to Manhiça District Hospital, prospective surveillance for invasive bacterial disease was conducted from June 2001 to May 2003. The level of antibiotic resistance of the isolates was also analysed.

RESULTS

Pneumococcus was the most commonly isolated bacterium, accounting for 212 episodes. The estimated crude incidence rate of IPD in the study area among children<5 years of age was 416/100,000 per child-year at risk. The youngest age group (<3 months) had the highest incidence (779/100,000). Cases were detected during both rainy and dry seasons. The most common clinical diagnosis was pneumonia, made in 146/212 (69%) of the episodes of IPD. The overall case fatality rate was 10%, being highest among children with pneumococcal meningitis (5/9=56%). Pneumococcal isolates were highly susceptible to penicillin (86% susceptible and 14% with intermediate resistance) and chloramphenicol (98% susceptible). In contrast, up to 37% of the isolates tested were non-susceptible to cotrimoxazole.

CONCLUSIONS

Incidence rates of IPD and associated mortality shown in this study highlight the need for pneumococcal vaccines in rural Africa, which must be effective in infants and young children.

Pneumococcal conjugate vaccines for preventing vaccine-type invasive pneumococcal disease and pneumonia with consolidation on x-ray in children under two years of age

BACKGROUND

Pneumonia, most commonly caused by Streptococcus pneumoniae (Pnc), is a major cause of morbidity and mortality among young children especially in developing countries. Recently, the prevalence of antibiotic-resistant Pnc has increased worldwide such that the effectiveness of preventive strategies, like the new pneumococcal conjugate vaccines (PCV) on rates of invasive pneumococcal disease (IPD) and pneumonia, needs to be evaluated.

OBJECTIVES

To determine the efficacy of PCV in reducing the incidence of IPD due to vaccine serotypes (VT) and x-ray confirmed pneumonia with consolidation of unspecified etiology in children who received PCV before 12 months of age.

SEARCH STRATEGY

We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 1 2004), MEDLINE (1990 to March 2004) and EMBASE (1990 to December 2003). Reference list of articles, and books of abstracts of relevant symposia, were hand searched. Researchers in the field were also contacted.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing PCV with placebo, or another vaccine, among children below two years with IPD and clinical/radiographic pneumonia as outcomes.

DATA COLLECTION AND ANALYSIS

Two reviewers independently identified eligible studies, assessed trial quality, and extracted data. Differences were resolved by discussion. The inverse variance method was used to pool effect sizes.

MAIN RESULTS

We identified four trials assessing the efficacy of PCV in reducing the incidence of IPD, two on x-ray confirmed pneumonia as outcome, and one on clinical pneumonia, with or without x-ray confirmation. Results from pooling HIV-1 negative children from the South African study with the other studies were as follows: the pooled vaccine efficacy (VE) for vaccine-type IPD was 88% (95% confidence interval (CI) 73% to 94%; fixed effect and random effects models), the effect measure was statistically significant (p <0.00001) and there was no heterogeneity (p = 0.77I2 0%); the pooled VE for all-serotype IPD was 66% (95% CI 46% to 79%; fixed effect model), the effect measure was statistically significant (p <0.00001) and there was no statistical heterogeneity (p = 0.09, I2 51%); the pooled VE for x-ray confirmed pneumonia was 22% (95% CI 11% to 31%; both fixed effect and random effects models) and there was no statistical heterogeneity (p = 0.80, I2 0%). Analyses that included all the children in the South African study (HIV-1 negative and HIV-1 positive children) and pooled with data from the other studies gave very similar results.

REVIEWERS' CONCLUSIONS

PCV is effective in reducing the incidence of IPD from all serotypes but exerts a greater effect in reducing VT IPD. Although PCV is also effective in reducing the incidence of x-ray confirmed pneumonia, there are still uncertainties about the definition of this outcome. Additional randomised controlled trials are currently in progress.

Vaccines in pregnancy: a review of their importance in Brazil

Neonates and young children remain susceptible to many serious infectious diseases preventable through vaccination. In general, current vaccines strategies to prevent infectious diseases are unable to induce protective levels of antibodies in the first 6 months of life. Women vaccinated during pregnancy are capable of producing immunoglobulin antibodies that are transported actively to the fetus, and maternal immunization can benefit both the mother and the child. With few exceptions, maternal immunization is not a routine, because of the concerns related to the safety of this intervention. Ethical and cultural issues make the studies on maternal immunization difficult; however, in the last decade, the development of new vaccines, which are very immunogenic and safe has reactivated the discussions on maternal immunization. In this paper we present a review of the literature about maternal immunization based on MEDLINE data (1990 to 2002). The most important conclusions are: 1) there is no evidence of risk to the fetus by immunizing pregnant women with toxoids, polysaccharide, polysaccharide conjugated and inactive viral vaccines; 2) most viral attenuated vaccines are probably safe too, but data is still insufficient to demonstrate their safety; therefore these vaccines should be avoided in pregnant women; 3) in Brazil, there is a need for a maternal immunization program against tetanus. Many new candidate vaccines for maternal immunization are available, but studies should be conducted to evaluate their safety and efficacy, as well as regional priorities based on epidemiological data.

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.

The genes encoding virulence-associated proteins and the capsule of Streptococcus pneumoniae are upregulated and differentially expressed in vivo

The polysaccharide capsule of Streptococcus pneumoniae and several well-characterized virulence proteins are known to contribute to the pathogenesis of pneumococcal disease. However, there is a paucity of data on the expression of their respective genes in vivo. In this study, the relative abundance of the mRNA transcripts of the genes encoding pneumolysin (ply), pneumococcal surface protein A (pspA), pneumococcal surface antigen A (psaA) and choline-binding protein A (cbpA), and of the first gene of the capsular polysaccharide biosynthesis locus (cps2A), was measured in virulent type 2 pneumococci harvested from the blood of BALB/c mice at 12 h and 24 h following intraperitoneal infection. The mRNA levels were then compared, using relative quantitative RT-PCR, with those present in organisms grown in serum broth. The expression of ply was upregulated threefold at 12 h, and 10-fold at 24 h post-infection; the expression of pspA and psaA was upregulated threefold and fivefold, respectively, at 12 h post-infection. Interestingly, the expression of pspA was 36-fold higher at 24 h post-infection whereas the expression of cps2A was upregulated approximately fourfold at 12 and 24 h post-infection. However, cbpA mRNA levels remained comparable in vivo and in vitro. When organisms were grown in whole blood or THY broth, the relative expression of these genes in the two growth media also differed markedly. This work provides direct molecular evidence that known virulence-associated genes of S. pneumoniae are differentially expressed in vivo. Data on the relative expression of these genes in different growth media also suggests that the regulation of expression of these genes is highly complex and multifactorial.

Pneumococcal conjugate vaccine: economic issues of the introduction of a new childhood vaccine

In February 2000, a pneumococcal conjugate vaccine was licensed for use in the USA. This vaccine has been shown to be effective in reducing pneumococcal disease, and has been recommended for universal use in infants. However, pneumococcal conjugate vaccine is by far the most expensive child vaccine series routinely administered in the USA, alone accounting for over 40% of the total purchase price of vaccines for the recommended childhood schedule. This article reviews the existing efficacy and economic studies of pneumococcal conjugate vaccine and discusses the process by which routine use of pneumococcal conjugate vaccine was introduced and the role economic analysis played in that process. Some of the scientific and funding issues relating to its use in both the industrialized and developing world are also discussed.

Materno-foetal transfer of H. influenzae and pneumococcal antibodies is influenced by prematurity and low birth weight: implications for conjugate vaccine trials

The influence of prematurity and low birth weight (LBW) on transplacental transfer of Haemophilus influenza type B and Streptococcus pneumoniae antibodies was assessed in 213 mothers and their neonates from Gambia. Paired maternal and cord serum samples were tested for specific IgG antibody titres for H. influenza and S. pneumococcus antigens using enzyme linked immunosorbent assay. Prematurity and LBW was significantly associated with reduced placental antibody transfer for these antigens.The reduced materno-foetal transfer of these antibodies in this vulnerable population of babies may further predispose them to more bacterial infections. These findings are of practical importance to the vaccination strategies.

Maternal immunization with pneumococcal polysaccharide vaccine in the third trimester of gestation

In a randomized, double blinded study, 23-valent pneumococcal polysaccharide vaccine (PSV) or conjugate Haemophilus influenzae type b (HbOC) vaccine was administered to 60 healthy women in the third trimester of gestation. Total IgG, IgG1, and IgG2 antibodies to pneumococcal serotypes 6B, 14, 19F and 23F were measured by ELISA in mothers prior to immunization, at delivery and 7 months after delivery, and in infants at birth (cord blood), 2 and 7 months after delivery. IgA was evaluated in breast milk at 2 and 7 months, and opsonophagocytic activity in cord blood. PSV was safe and immunogenic in pregnant women. Transplacental transmission of vaccine-specific antibodies was efficient. Maternal immunization with PSV resulted in significantly higher concentrations of pneumococcal antibodies in infants at birth and at 2 months of age, and greater functional opsonophagocytic activity of passively acquired IgG antibody.

Immunization with components of two iron uptake ABC transporters protects mice against systemic Streptococcus pneumoniae infection

There has been considerable recent research into protein based Streptococcus pneumoniae vaccines as alternatives to the existing capsular antigen vaccines. PiuA and PiaA (formerly Pit1A and Pit2A) are recently identified lipoprotein components of S. pneumoniae iron uptake ABC transporters which are required for full virulence and are likely to be expressed on the surface of the bacterial cell membrane. We investigated the efficacy of recombinant PiuA and PiaA proteins at eliciting protective immunity in mice against systemic infection with S. pneumoniae. Both recombinant PiuA and PiaA generated antibody responses that cross-reacted with each other but not with pneumolysin and reacted with identical proteins from nine different S. pneumoniae serotypes. Mice immunized with recombinant PiuA and PiaA were protected against systemic challenge to a degree similar to those immunized with an existing protein vaccine candidate, PdB (a genetically modified pneumolysin toxoid). Immunization with a combination of both PiuA and PiaA resulted in additive protection and was highly protective against systemic infection with S. pneumoniae. PiuA and PiaA are therefore promising additional candidates for a novel S. pneumoniae vaccine using protein antigens.

Protection against Streptococcus pneumoniae elicited by immunization with pneumolysin and CbpA

The need for the development of cheap and effective vaccines against pneumococcal disease has necessitated the evaluation of common virulence-associated proteins of Streptococcus pneumoniae as potential vaccine antigens. In this study, we examined the capacity of active immunization with a genetic toxoid derivative of pneumolysin (PdB) and/or a fragment of choline binding protein A (CbpA; also known as PspC, Hic, and SpsA) to protect mice from intraperitoneal challenge with medium to very high doses of a highly virulent capsular type 2 pneumococcal strain, D39. The median survival times for mice immunized with the individual protein antigens in different adjuvant combinations were significantly longer than those for mice that received the respective adjuvants alone. Mice immunized with CbpA alone were significantly better protected than mice immunized with PdB alone. Correspondingly, the median survival times for mice that were immunized with a combination of PdB and CbpA were significantly longer than those for mice that received PdB alone but not significantly different from those that received CbpA alone. Mice immunized with the protein antigens in a mixture of monophospholipid A (MPL) and aluminium phosphate (AlPO4) adjuvants had higher antibody titers than mice that received the antigens in AlPO4 alone. Mice immunized with PdB in MPL plus AlPO4 were also significantly better protected than mice that received PdB in AlPO4 alone.