Vaccines for children in rich and poor countries

Pneumococcal antibody concentrations of subjects in communities fully or partially vaccinated with a seven-valent pneumococcal conjugate vaccine

Background

A recent trial with PCV-7 in a rural Gambian community showed reduced vaccine-type pneumococcal carriage in fully vaccinated compared with control communities. We measured pneumococcal polysaccharide antibody concentrations in this trial to understand further the mechanisms underlying the observed changes.

Methods

A single-blind, cluster-randomized (by village) trial was conducted in 21 Gambian villages. In 11 villages, all residents received PCV-7 (Vaccine group); in 10 control villages only children <30 months old or those born during the study received PCV-7. Subjects over the age of 30 months resident in vaccine villages received a single dose of PCV-7 whilst those in control villages received a single dose of a serogroup C meningococcal conjugate vaccine. Serum antibody concentrations against specific pneumococcal polysaccharides were measured in approximately 200 age-stratified subjects before, 4–6, 12 and 24 months following vaccination.

Results

Baseline pneumococcal antibody concentrations were generally high and increased with age up to 10 years. One dose of PCV-7 increased geometric mean antibody concentrations (GMC) in vaccinated versus control villages for vaccine serotypes 6B and 18C, and 4 and 18C, in the young (under 5 years) and older age groups (5+ years) respectively. There were significantly higher proportions of subjects in the vaccinated than in the control communities with an antibody concentration believed to protect against carriage (>5.0 µg/mL) for all but serotype 9V of the PCV-7 serotypes in the older group, but not in the younger age group.

Conclusion

Higher antibodies in vaccinated communities provide an explanation for the lower pneumococcal carriage rates in fully vaccinated compared to control communities.

Trial Registration

Controlled-Trials.com ISRCTN51695599 51695599.

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.

A systematic review on the diagnosis of pediatric bacterial pneumonia: when gold is bronze

Background

In developing countries, pneumonia is one of the leading causes of death in children under five years of age and hence timely and accurate diagnosis is critical. In North America, pneumonia is also a common source of childhood morbidity and occasionally mortality. Clinicians traditionally have used the chest radiograph as the gold standard in the diagnosis of pneumonia, but they are becoming increasingly aware that it is not ideal. Numerous studies have shown that chest radiography findings lack precision in defining the etiology of childhood pneumonia. There is no single test that reliably distinguishes bacterial from non-bacterial causes. These factors have resulted in clinicians historically using a combination of physical signs and chest radiographs as a ‘gold standard’, though this combination of tests has been shown to be imperfect for diagnosis and assigning treatment. The objectives of this systematic review are to: 1) identify and categorize studies that have used single or multiple tests as a gold standard for assessing accuracy of other tests, and 2) given the ‘gold standard’ used, determine the accuracy of these other tests for diagnosing childhood bacterial pneumonia.

Methods and Findings

Search strategies were developed using a combination of subject headings and keywords adapted for 18 electronic bibliographic databases from inception to May 2008. Published studies were included if they: 1) included children one month to 18 years of age, 2) provided sufficient data regarding diagnostic accuracy to construct a 2×2 table, and 3) assessed the accuracy of one or more index tests as compared with other test(s) used as a ‘gold standard’. The literature search revealed 5,989 references of which 256 were screened for inclusion, resulting in 25 studies that satisfied all inclusion criteria. The studies examined a range of bacterium types and assessed the accuracy of several combinations of diagnostic tests. Eleven different gold standards were studied in the 25 included studies. Criterion validity was calculated for fourteen different index tests using eleven different gold standards. The most common gold standard utilized was blood culture tests used in six studies. Fourteen different tests were measured as index tests. PCT was the most common measured in five studies each with a different gold standard.

Conclusions

We have found that studies assessing the diagnostic accuracy of clinical, radiological, and laboratory tests for bacterial childhood pneumonia have used a heterogeneous group of gold standards, and found, at least in part because of this, that index tests have widely different accuracies. These findings highlight the need for identifying a widely accepted gold standard for diagnosis of bacterial pneumonia in children.

Migration and child immunization in Nigeria: individual- and community-level contexts

BACKGROUND

Vaccine-preventable diseases are responsible for severe rates of morbidity and mortality in Africa. Despite the availability of appropriate vaccines for routine use on infants, vaccine-preventable diseases are highly endemic throughout sub-Saharan Africa. Widespread disparities in the coverage of immunization programmes persist between and within rural and urban areas, regions and communities in Nigeria. This study assessed the individual- and community-level explanatory factors associated with child immunization differentials between migrant and non-migrant groups.

METHODS

The proportion of children that received each of the eight vaccines in the routine immunization schedule in Nigeria was estimated. Multilevel multivariable regression analysis was performed using a nationally representative sample of 6029 children from 2735 mothers aged 15-49 years and nested within 365 communities. Odds ratios with 95% confidence intervals were used to express measures of association between the characteristics. Variance partition coefficients and Wald statistic i.e. the ratio of the estimate to its standard error were used to express measures of variation.

RESULTS

Individual- and community contexts are strongly associated with the likelihood of receiving full immunization among migrant groups. The likelihood of full immunization was higher for children of rural non-migrant mothers compared to children of rural-urban migrant mothers. Findings provide support for the traditional migration perspectives, and show that individual-level characteristics, such as, migrant disruption (migration itself), selectivity (demographic and socio-economic characteristics), and adaptation (health care utilization), as well as community-level characteristics (region of residence, and proportion of mothers who had hospital delivery) are important in explaining the differentials in full immunization among the children.

CONCLUSION

Migration is an important determinant of child immunization uptake. This study stresses the need for community-level efforts at increasing female education, measures aimed at alleviating poverty for residents in urban and remote rural areas, and improving the equitable distribution of maternal and child health services.

The impact of indirect (herd) protection on the cost-effectiveness of pneumococcal conjugate vaccine

BACKGROUND

The heptavalent pneumococcal polysaccharide-protein conjugate vaccine (PCV7) confers protection against invasive pneumococcal disease (IPD) caused by serotypes that are responsible for substantial morbidity and mortality throughout the world. In 2000, the 7 serotypes covered by PCV7 accounted for 80% to 90% of serotypes isolated from the blood or cerebrospinal fluid of children aged <6 years in the United States. A previous review of the literature spanning the years 1998 to 2005 pertaining to the incidence of IPD among nonimmunized individuals in countries with universal PCV7 immunization suggested an indirect protective effect (herd protection, or community immunity) after widespread vaccination. Consideration of indirect protection against IPD may enhance cost-benefit evaluations of vaccination programs.

OBJECTIVE

The objective of this analysis was to review the literature on cost-effectiveness analyses of PCV7 vaccination to determine whether inclusion of the indirect effect in decision-analysis models substantially affects the cost-effectiveness findings in favor of vaccination.

METHODS

A literature review of cost-effectiveness analyses of PCV7 vaccination was conducted using the DIMDI (Deutschen Institut fur Medizinische Dokumentation und Information) superbase, which comprises 12 databases, to identify articles published between January 2000 and October 2006 using the search terms 7-valent pneumococcal conjugate vaccine AND herd immunity/herd effect, and 7-valent pneumococcal conjugate vaccine AND cost-effectiveness, cost-utility, or cost-benefit analyses. Monetary values were converted to euros and inflated to 2006 values, and events avoided were converted to rates per 100,000 vaccinated to allow comparison across studies. The sensitivity analyses from the models that included indirect effects were examined.

RESULTS

There was wide variability in the health-economic results of the 16 studies that met the inclusion criteria. In studies that did not include indirect effects, the adjusted cost per life-year gained ranged from cost saving to euro140,723 from the societal perspective and from euro56,724 to euro324,218 from the payer perspective. In the 4 studies that included indirect effects, a significant and consistent improvement was seen in the health-economic results in favor of vaccination with PCV7. No trends in variability across time or geographic region were observed.

CONCLUSIONS

Indirect effects had a significant effect on cost-effectiveness, as seen in the sensitivity analyses. Future models should include indirect effects in evaluating the cost-effectiveness of PCV7.

Impact of conflict on infant immunisation coverage in Afghanistan: a countrywide study 2000-2003

BACKGROUND

Infant immunisation is an effective public health intervention to reduce the morbidity and mortality of vaccine preventable diseases. However, some developing countries fail to achieve desirable vaccination coverage; Afghanistan is one such country. The present study was performed to evaluate the progress and variation in infant immunisation coverage by district and region in Afghanistan and to assess the impact of conflict and resource availability on immunisation coverage.

RESULTS

This study analysed reports of infant immunisation from 331 districts across 7 regions of Afghanistan between 2000 and 2003. Geographic information system (GIS) analysis was used to visualise the distribution of immunisation coverage in districts and to identify geographic inequalities in the process of improvement of infant immunisation coverage. The number of districts reporting immunisation coverage increased substantially during the four years of the study. Progress in Bacillus Calmette-Guerin (BCG) immunisation coverage was observed in all 7 regions, although satisfactory coverage of 80% remained unequally distributed. Progress in the third dose of Diphtheria-Pertussis-Tetanus (DPT3) immunisation differed among regions, in addition to the unequal distribution of immunisation coverage in 2000. The results of multivariate logistic regression analysis indicated a significant negative association between lack of security in the region and achievement of 80% coverage of immunisation regardless of available resources for immunisation, while resource availability showed no relation to immunisation coverage.

CONCLUSION

Although progress was observed in all 7 regions, geographic inequalities in these improvements remain a cause for concern. The results of the present study indicated that security within a country is an important factor for affecting the delivery of immunisation services.

A prospective three-year cohort study of the epidemiology and virology of acute respiratory infections of children in rural India

Background

Acute respiratory infection (ARI) is a major killer of children in developing countries. Although the frequency of ARI is similar in both developed and developing countries, mortality due to ARI is 10–50 times higher in developing countries. Viruses are common causes of ARI among such children, yet the disease burden of these infections in rural communities is unknown.

Methodology/Principal Findings

A prospective longitudinal study was carried out in children enrolled from two rural Indian villages at birth and followed weekly for the development of ARI, classified as upper respiratory infection, acute lower respiratory infection (ALRI), or severe ALRI. Respiratory syncytial virus (RSV), influenza, parainfluenza viruses and adenoviruses in nasopharyngeal aspirates were detected by direct fluorescent antibody testing (DFA) and, in addition, centrifugation enhanced culture for RSV was done. 281 infants enrolled in 39 months and followed until 42 months. During 440 child years of follow-up there were 1307 ARIs, including 236 ALRIs and 19 severe ALRIs. Virus specific incidence rates per 1000 child years for RSV were total ARI 234, ALRI 39, and severe ALRI 9; for influenza A total ARI 141, ALRI 39; for INF B total ARI 37; for PIV1 total ARI 23, for PIV2 total ARI 28, ALRI 5; for parainfluenza virus 3 total ARI 229, ALRI 48, and severe ALRI 5 and for adenovirus total ARI 18, ALRI 5. Repeat infections with RSV were seen in 18 children.

Conclusions/Significance

RSV, influenza A and parainfluenza virus 3 were important causes of ARI among children in rural communities in India. These data will be useful for vaccine design, development and implementation purposes.

Prevalence of IgG antibody against measles, mumps and rubella in bangladeshi children: a pilot study to evaluate the need for integrated vaccination strategy

The present study was carried out to determine the seroprevalence of IgG antibodies in Bangladeshi children against measles (irrespective of vaccination status), mumps and rubella (MMR) to assess strategic need of combined vaccination for these diseases. A total of 456 children of 1 month to 15 years, were studied. Serum IgG antibodies against MMR were measured by enzyme-linked immunosorbent assay (ELISA). By 3 months, protective IgG antibody level (>40 AU for measles and mumps and >15 IU/ml for rubella) for the diseases found to be between 50% and 80% among the studied children. Protective measles antibody (IgG) was not detected in all the children of 3-9 months and significant number of children between 9 months and 5 years were unprotected (87-65%; P < 0.001). Moreover, children of 3-15 months had no protective antibody level against mumps and significant number of children between 15 months and 5 years were unprotected (92-71%; P < 0.001). Between 5 and 15 years of age, significant number of children became protective (63-85%, P < 0.001). Although, a majority of children between 3 months and 5 years had shown to have no protective antibody against rubella (89-71%; P < 0.01-0.001) between >10 and 15 years 71% children had protective level of antibodies (P < 0.001). No significant difference was observed in antibody prevalence regarding socioeconomic classes, nutritional status and parental education. The data showed that: (i) a significant number of children remain unprotected against MMR in childhood and (ii) an extensive nationwide survey is required to suggest an integrated vaccination strategy in order to implement appropriate control measures of the three infectious diseases.

In vitro and in vivo fitness of respiratory syncytial virus monoclonal antibody escape mutants

Respiratory syncytial virus (RSV) is the only infectious disease for which a monoclonal antibody (MAb) is used in humans. Palivizumab (PZ) is a humanized murine MAb to the F protein of RSV. PZ-resistant viruses appear after in vitro and in vivo growth of RSV in the presence of PZ. Fitness for replication could be a determinant of the likelihood of dissemination of resistant viruses. We assessed the fitness of two PZ-resistant viruses (F212 and MP4). F212 grew less well in cell culture than the parent A2 virus and was predicted to be less fit than A2. Equal amounts of F212 and A2 were mixed and passaged in cell culture. F212 disappeared from the viral population, indicating it was less fit than the A2 virus. The MP4 virus grew as well as A2 in culture and in cotton rats. A2/MP4 virus input ratios of 1:1, 10:1, 100:1, and 1,000:1 were compared in competitive replication. For all input ratios except 1,000:1, the MP4 virus became dominant, supplanting the A2 virus. The MP4 virus also dominated the A2 virus during growth in cotton rats. Thus, the mutant MP4 virus was more fit than A2 virus in both in vitro and in vivo competitive replication. Whether this fitness difference was due to the identified nucleotide substitutions in the F gene or to mutations elsewhere in the genome is unknown. Understanding the mechanisms by which mutant virus fitness increased or decreased could prove useful for consideration in attenuated vaccine design efforts.

Genetic variability in the G protein gene of group A and B respiratory syncytial viruses from India

Respiratory syncytial virus (RSV) is the most commonly identified viral agent of acute respiratory tract infection (ARI) of young children and causes repeat infections throughout life. Limited data are available on the molecular epidemiology of RSV from developing countries, including India. This study reports on the genetic variability in the glycoprotein G gene among RSV isolates from India. Reverse transcription-PCR for a region of the RSV G protein gene was done with nasopharyngeal aspirates (NPAs) collected in a prospective longitudinal study in two rural villages near Delhi and from children with ARI seen in an urban hospital. Nucleotide sequence comparisons among 48 samples demonstrated a higher prevalence of group A (77%) than group B (23%) RSV isolates. The level of genetic variability was higher among the group A viruses (up to 14%) than among the group B viruses (up to 2%). Phylogenetic analysis revealed that both the GA2 and GA5 group A RSV genotypes were prevalent during the 2002-2003 season and that genotype GA5 was predominant in the 2003-2004 season, whereas during the 2004-2005 season both genotype GA5 and genotype BA, a newly identified group B genotype, cocirculated in almost equal proportions. Comparison of the nonsynonymous mutation-to-synonymous mutation ratios (dN/dS) revealed greater evidence for selective pressure between the GA2 and GA5 genotypes (dN/dS, 1.78) than within the genotypes (dN/dS, 0.69). These are among the first molecular analyses of RSV strains from the second most populous country in the world and will be useful for comparisons to candidate vaccine strains.

Immunogenicity and safety of four different doses of Haemophilus influenzae type b-tetanus toxoid conjugated vaccine, combined with diphtheria–tetanus–pertussis vaccine (DTP-Hib), in Indonesian infants

Widespread use of Haemophilus influenzae type b (Hib) conjugated vaccine in industrialized countries has resulted in a dramatic decline in the incidence of invasive Hib diseases, but the vaccine's cost has prevented its inclusion in basic immunization programs in developing countries. To overcome this problem, combination with diphtheria-tetanus-pertussis (DTP) vaccine or reduction in the dose of Hib vaccine has been proposed. To evaluate the immunogenicity and adverse reactions from lower doses of Hib-polyribosylphosphate (PRP) conjugated with tetanus toxoid (PRP-T), a double-blind study was conducted in Jakarta, Indonesia, and its suburbs. A total of 1048 infants 6 weeks to 6 months of age received three doses of DTP vaccine combined with the usual 10 microg dose or with a reduced dose of 5, 2.5 or 1.25 microg of PRP-T at two-monthly intervals. Antibodies were measured prior to the first dose and 4-6 weeks following the third dose. Adverse reactions were similar among all four groups. The only significant difference was a higher rate of irritability (p<0.02) and of temperature elevation >38 degrees C (p<0.009) after doses 1 and 2 in the lowest dose group (1.25 microg PRP-T) compared to the other groups. All participants tested had a 4-fold increase in antibodies against all DTP antigens. In addition, after a fourth booster dose of Hib, 99.6% of infants produced >or=0.15 microg/ml of antibody to Hib-PRP, and 96.4% showed levels >or=1.0 microg/ml after primary immunization, level that correlate with short- and long-term immunity, respectively. Antibody titers to the PRP antigen showed no significant differences among dosage groups with the exception of the 5.0 microg group, which had a significantly higher GMC than the 1.25 microg group (p<0.012). This study demonstrates that primary vaccination with half, one-fourth, or one-eighth of the usual dose of PRP-T, combined with DTP vaccine, produces protective immune responses, and has side effects that are comparable to DTP vaccination alone. In these lower dosages, PRP-T conjugate vaccine can lower vaccine costs to a level that is affordable for infant immunization programs in developing countries.

Reducing the global burden of sepsis in infants and children: a clinical practice research agenda

OBJECTIVE

Sepsis remains a predominant cause of mortality and morbidity in children in the developing and industrialized world. This review discusses a clinical practice research agenda to reduce this global burden.

DESIGN

Summary of the literature with analysis by experts.

RESULTS

Many interventions have been proven effective in decreasing sepsis. Heterologous immunization with attenuated Bacillus Camille Guerin vaccine reduces all-cause mortality, and specific immunizations further reduce morbidity and mortality from many specific microbes. Antepartum antibiotics reduce the prevalence of cerebral palsy and mortality in infants. Administration of antibiotics to neonates with signs of sepsis reduces all-cause mortality five-fold and can also reduce mortality in the big four killers of children: severe pneumonia, diarrhea, malaria, or measles. Immunonutrition with zinc and vitamin A can further reduce morbidity in diarrhea and pneumonia and reduce mortality in measles. First-hour rapid intravenous fluid resuscitation achieves 100% survival in dengue shock, and time-sensitive fluid resuscitation and inotropic support reduces mortality ten-fold in meningococcal septic shock. Multiple organ failure occurs when late or inadequate resuscitation results in systemic thrombosis or when infection is not eradicated because of immunosuppression or inadequate source control.

CONCLUSIONS

The global burden of sepsis can be reduced by 1) prevention with improved heterologous or specific vaccines and vitamin or mineral supplement programs; 2) early recognition and treatment with appropriate antibiotics, intravenous fluid resuscitation, and inotropic support in organized healthcare-delivery systems; and 3) development of new diagnostics and therapeutics that reduce systemic thrombosis, improve immune function, and kill resistant organisms.

Modeling diarrhea disease in children less than 5 years old

PURPOSE

Identification of the temporal pattern of diarrhea disease in children less than 5 years of age in Rio de Janeiro City (1995-1998) to provide support for decisions about prevention and control of the disease.

METHODS

The weekly counts of hospitalizations and deaths due to diarrhea disease were analyzed separately. An initial generalized linear model (GLM) was derived using variables related to weather and month. Displays of fitted generalized additive models (GAM) including a spline smoothed function of time suggested additional predictors that were used to obtain new models.

RESULTS

The initial models did not properly account for the observed cyclical pattern of the data. Graphical displays of the GAM model show a nonhomogeneous decline and annual cycles. Stepwise fitting of GLMs with two factors (cycle and season), and a time trend, showed that the full three-way interaction model was required. Plots of the residuals from the death model suggested a mixture of distributions while the residuals from the hospitalization model were approximately normal.

CONCLUSIONS

The same general pattern for both time series was found by graphical inspection and fitting of appropriate GLMs. This study provides some additional evidence that severe cases of diarrhea disease may be attributed to rotavirus.

Population-based surveillance of pediatric pneumonia: use of spatial analysis in an urban area of Central Brazil

This study examined the spatial distribution of childhood community-acquired pneumonia detected through prospective surveillance in Goiânia, Brazil. Three spatial analysis techniques were applied to detect intra-urban geographic aggregation of pneumonia cases: Kernel method, nearest neighbor hierarchical technique, and spatial scan statistic. A total of 724 pneumonia cases confirmed by chest radiography were identified from May 2000 to August 2001. All cases were geocoded on a digital map. The annual pneumonia risk rate was estimated at 566 cases/100,000 children. Analysis using traditional descriptive epidemiology showed a mosaic distribution of pneumonia rates, while GIS methodologies showed a non-random pattern with hot spots of pneumonia. Cluster analysis by spatial scan statistic identified two high-risk areas for pneumonia occurrence, including one most likely cluster (RR = 2.1; p < 0.01) and one secondary cluster (RR = 1.3; p = 0.01). The data used for the study are in line with recent WHO-led efforts to improve and standardize pediatric pneumonia surveillance in developing countries and show how GIS and spatial analysis can be applied to discriminate target areas of pneumonia for public heath intervention.

Padrão temporal das internações e óbitos por diarréia em crianças, 1995 a 1998, Rio de Janeiro

OBJETIVO: Analisar o padrão temporal dos óbitos e internações, no período de 1995 a 1998, associadas à diarréia em crianças menores de cinco anos de idade para subsidiar ações específicas de prevenção e controle dessa doença. MÉTODOS: Os dados foram obtidos do Sistema de Informações sobre Mortalidade (SIM) e Sistema de Internações Hospitalares (SIH) do Ministério da Saúde. As séries mensais de internações e de óbitos por diarréia foram decompostas em componentes de tendência linear estocástica, sazonalidade determinística e irregularidades mediante a aplicação dos modelos estruturais para análise de séries temporais. RESULTADOS: Os níveis de ambas as séries apresentaram mudanças ao longo do tempo, com declínio mais perceptível na série de internações. A variação das taxas de inclinação foi constante para cada uma das séries, em média, a menos 5,3 internações por mês (p-valor <0,001) e menos um óbito por mês (p-valor <0,1), respectivamente. Na análise dos resíduos do modelo de internações, observou-se mudança no nível da tendência em janeiro de 1996. O componente sazonal de ambos os modelos foi estatisticamente significante (p-valor <0,0001), sendo maio e junho os meses com maior excesso de internações e óbitos. Os pressupostos de normalidade e de independência temporal dos resíduos não puderam ser rejeitados ao nível de 0,05. CONCLUSÕES: Os resultados sugerem a predominância da etiologia viral das diarréias moderadas e graves. Neste caso, a vacinação específica é a medida mais eficaz na prevenção e controle, sendo necessários estudos de eficácia de novas candidatas à vacina contra o rotavírus no Brasil.

Nosocomial outbreaks--a potential threat to the elimination of measles?

A suspected nosocomial outbreak of measles among children in the largest hospital in Southern Africa is described. The outbreak occurred from June to August 1999. Due to geographic differences in the areas where the patients lived, it is unlikely they came into contact with measles in the community. In contrast, all but the first case was in the ward of origin when another child was present with clinical signs and symptoms of measles. All but the first child had subsequent laboratory confirmation of acute measles infection. This outbreak occurred after the launch of the measles elimination effort in South Africa. The implications of nosocomial transmission of measles on the elimination effort are discussed.

Vaccines for children: policies, politics and poverty

The dawn of the 21st century ushered in spectacular advances in vaccine production technology. However, the benefits of these developments have been largely confined to the world's most affluent and least afflicted. Of the 14 million deaths that occur world-wide in children aged less than 5 years, over 95% of these occur in developing countries and at least 70% are caused by infections for which vaccines are already available in other countries. While impoverished countries do not have a right to be assisted with the provision of funds or vaccines by affluent developed countries, an initiative for the global eradication of a vaccine preventable disease, requires a global effort. Assisting developing countries to achieve such goals should be a high priority for wealthy nations, even if only to protect their own populations. With improved international travel, not only can newly emerging diseases spread across the globe, but pathogens eliminated from one population can be re-imported by travellers or immigrants. In contrast, the recent decline in acceptance of immunisation programmes in developed countries are secondary to strong anti-vaccine movements attributing unproven adverse reactions to vaccines, placing these life-saving vaccines into disrepute. A fertile ground for propagation of these ideologies is created by parents who in their lifetime may not have seen a child killed or maimed from bacterial meningitis or measles and therefore have little understanding of the risk-benefit of vaccination. The development and deployment of vaccines must be a global effort as are the treaties for global disarmament for weapons of mass destruction.

Serotype distribution and antimicrobial resistance of Streptococcus pneumoniae isolated in Algiers, Algeria

There are few data on antibiotic resistance of Streptococcus pneumoniae in Algeria. Among 309 strains, 34.6% were penicillin G-nonsusceptible S. pneumoniae strains (25.2% were intermediate and 9.4% were resistant). Serotypes 1, 5, 14, and 6 were the most frequent in invasive child infections. A multicenter study to standardize the national guidelines is needed.

The epidemiology of mental retardation: challenges and opportunities in the new millennium

There are a number of problems and challenges in relating the science of epidemiology to mental retardation (MR). These relate to how MR is defined and classified and how these definitions may change over time. These as well as other differences in ascertainment sources and methods need to be considered when comparing MR prevalence over time and place. On the other hand, advances in technology also provide new and efficient methods of data collection both by data linkage and by use of web-based methods to study rare diseases. While prevalence studies have not been individually reviewed, we have examined the range of data including recent studies relating to how prevalence differs according to age, gender, social class and ethnicity. Some problems with available etiological classification systems have been identified. Recent etiological studies, most of which use different classification systems, have been reviewed and explanations have been postulated to account for differences in results. Individual risk factors for MR are considered whilst the option of considering a population as opposed to a high risk strategy to MR prevention is raised. This might well involve improving the social milieu surrounding the occurrence of individual risk factors. The impact of biotechnological advances such as antenatal and neonatal screening and assisted reproduction on MR are discussed. The issue of how inequalities in access to technology may impact on case identification and even have the potential to further widen inequalities is raised. The importance of extending the use of epidemiological tools to study the social, health and economic burden of MR is also emphasized. However, in order to apply to MR the "prevention-intervention-research" cycle, which surely underpins all epidemiology, it is vital to ensure that the methodological challenges we raise are adequately addressed.

Maternal immunization with pneumococcal polysaccharide vaccine in the highlands of Papua New Guinea

In Tari, Southern Highlands Province (SHP), Papua New Guinea (PNG), pneumococcal polysaccharide (Pnc PS) vaccine was offered to women at 28-38 weeks gestation. Blood samples were collected for measurement of pneumococcal antibody titres prior to immunization, from mother and cord at delivery and from their children at ages 1-3 and 4-6 months; samples were also collected in a subset of children before and 1 month after Pnc PS vaccine was given at age 8-9 months. Serum was collected from unimmunized women and their children at delivery and from children of unimmunized women at the same ages in infancy. There were no differences in neonatal or post-neonatal mortality rates or congenital abnormalities in the children of 235 immunized and 202 unimmunized women. There was a significant increase in antibody titres to pneumococcal serotypes 5, 14 and 23F in immunized women but not for serotype 7F. Geometric mean titres (GMTs) of antibodies for serotypes 5 and 23F were significantly higher in children of immunized women than in the unimmunized group up to age 2 months and for serotype 14 significantly higher to age 4 months. Maternal immunization did not significantly affect the children's capacity to make antibody responses to immunization with Pnc PS vaccine in infancy. The findings of this study and those in several other developing countries provide support for the concept of Pnc PS maternal immunization and justify the planning of large-scale efficacy trials.

Vitamin A supplementation at birth delays pneumococcal colonization in South Indian infants

Nasopharyngeal colonization is a risk factor for pneumococcal disease, a leading cause of complications and death in infants. We assessed the impact of vitamin A supplementation in reducing pneumococcal colonization in infants from an area with endemic vitamin A deficiency. We recruited 464 2-mo-old infants from a rural area in South India. Infants were randomly assigned to receive two 7000-microg retinol equivalent doses of vitamin A (n = 239) or placebo (n = 225) orally at birth, and nasopharyngeal specimens were collected at ages 2, 4 and 6 mo. We studied the effect of vitamin A on culture-confirmed pneumococcal colonization and on the distribution of pneumococcal serotypes. Analyses were conducted by intention-to-treat. The risk of colonization among infants aged 4 mo who were not colonized by age 2 mo was significantly reduced in the vitamin A group compared with the placebo group [odds ratio 0.51 (0.28, 0.92), P = 0.02). The odds of colonization were 27% lower in the treatment group than in the placebo group [odds ratio 0.73 (0.48, 1.1), P = 0.13]. No differences were detected in the prevalence of invasive serotypes. The risk of colonization with penicillin-resistant isolates was 74% lower in the vitamin A group than in the placebo group at 2 mo of age. However, the prevalence of penicillin-resistant isolates was only 4%. Neonatal vitamin A supplementation may play a role in lowering morbidity rates associated with pneumococcal disease by delaying the age at which colonization occurs.

Prospects for pneumococcal vaccination in African children

Streptococcus pneumoniae (pneumococcus) remains a major cause of morbidity and mortality in both developed and undeveloped countries. Accurate disease burden estimates for developing countries and Africa in particular, where diagnostic facilities are less adequate and a disease surveillance system virtually non-existent, is difficult. However, from conservative estimates, the pneumococcus is probably responsible for at least 1 million of the 4 million deaths that occur from acute lower respiratory infections in children aged less than 5 years. The global burden of disease has been accentuated by the rising menace of multi-drug resistant strains, which defy geographic and racial borders. Thus, now more than ever before, there is an urgent need to identify and implement preventive measures to avert this problem. The currently licensed pneumococcal polysaccharide vaccine, comprises 23 capsular polysaccharides of the pneumococcus, many of which are poorly immunogenic in the very vulnerable age group of under-fives. A possible solution to the problem of poor immunogenicity is to use a protein/polysaccharide conjugate vaccine similar to that recently introduced successfully for Haemophilus influenzae type b (Hib) and using this approach, several workers have reported promising results from safety and immunogenicity studies. However, unlike Hib, the development of conjugate vaccine against pneumococcal disease is complicated by the existence of more serotypes than can be feasibly incorporated in a single conjugate vaccine formulation. Whilst this challenge has been taken on by some vaccine manufacturers, novel approaches such as the identification or construction of protective protein antigen, common to all clinically important strains are being explored. Novel application of the pneumococcal polysaccharide vaccines in pregnancy for protection of disease in early infancy is an approach that has not been evaluated. For maximum impact, the ultimate vaccine formulation should be affordable and available to resource poor countries where the burden of disease is highest. Establishing disease surveillance systems in such countries now will greatly facilitate the introduction of the vaccines.