Measuring the impact of conjugate vaccines on invasive Haemophilus influenzae type b infection in Western Australia

Effectiveness of Haemophilus influenzae type b vaccines administered according to various schedules: systematic review and meta-analysis of observational data

BACKGROUND

Conjugate vaccines against Haemophilus influenzae type b (Hib) are widely used. The full implications of Hib vaccination schedule for vaccine effectiveness (VE) are unclear.

METHODS

We searched the literature for observational studies reporting the effectiveness of conjugate Hib vaccines administered according to different schedules. We summarized dose-specific VE estimates, where appropriate, using random effects meta-analysis.

RESULTS

Thirty-one eligible articles (reporting 30 studies conducted in 17 countries) were identified. Meta-analysis of case-control studies using community controls produced VE estimates against Hib meningitis of 55% (95% confidence interval: 2-80%, based on 3 studies), 96% (86-99%, 3 studies) and 96% (86-99%, 4 studies) after 1, 2 and 3 doses of vaccines other than the polyribosyl ribitol phosphate outer membrane protein vaccine. Estimates were similar using hospital controls. VE against invasive Hib disease in case-control studies was estimated as 59% (30-76%, 3 studies) and 97% (87-99%, 3 studies) for 1 and 3 doses (insufficient data were identified to estimate 2-dose VE). Point estimates from 2 studies suggested VE>90% after 1 dose of the polyribosyl ribitol phosphate outer membrane protein vaccine, but meta-analysis was not possible. Using data from 4 cohort studies, 3-dose VE was estimated as 94% (88-97%). There was some evidence that Hib vaccine was less effective when administered with acellular (rather than whole cell) pertussis vaccine. Weak evidence from 2 studies suggested that a booster confers some additional protection following full primary vaccination and may compensate for an incomplete primary series.

CONCLUSIONS

Observational data suggest that ≥2 doses of Hib vaccine are required for high effectiveness, but do not strongly favor any particular schedule.

Haemophilus influenzae type b conjugate vaccines - a South African perspective

Introduction of Hib vaccine is known to positively impact on reduction of both morbidity and mortality in children less than 5 years of age. Incorporation of this vaccine into a National EPI, however, does come at a significant cost, which is especially important in non-GAVI funded countries. Compounded reduction in response in certain patient populations and possible indication of booster doses further impacts on cost-benefit analyses. Despite these issues, South Africa has supplied Hib vaccine as part of the National EPI in the form of a combination vaccine, Pentaxim, which combines Hib with Diphtheria, Tetanus, acellular Pertussis (DTP) and Poliomyelitis since 2009. Prior to this, another combination vaccine was utilized containing Hib and DTP. This has subsequently lead to a significant reduction in invasive Hib disease post-introduction, therefore largely justifying utilization.

The impact of new vaccine introduction on immunization and health systems: a review of the published literature

We conducted a systematic review of the published literature to examine the impact of new vaccine introduction on countries' immunization and broader health systems. Six publication databases were searched using 104 vaccine and health system-related search terms. The search yielded 15,795 unique articles dating from December 31, 1911 to September 29, 2010. Based on review of the title and abstract, 654 (4%) of these articles were found to be potentially relevant and were referred for full review. After full review, 130 articles were found to be relevant and included in the analysis. These articles represented vaccines introduced to protect against 10 different diseases (hepatitis A, hepatitis B, Haemophilus influenzae type b disease, human papilloma virus infection, influenza, Japanese encephalitis, meningococcal meningitis, Streptococcus pneumoniae disease, rotavirus diarrhea and typhoid), in various formulations and combinations. Most reviewed articles (97 [75%]) reported experiences in high-income countries. New vaccine introduction was most efficient when the vaccine was introduced into an existing delivery platform and when introduced in combination with a vaccine already in the routine childhood immunization schedule (i.e., as a combination vaccine). New vaccine introduction did not impact coverage of vaccines already included in the routine childhood immunization schedule. The need for increased cold chain capacity was frequently reported. New vaccines facilitated the introduction and widespread use of auto-disable syringes into the immunization and the broader health systems. The importance of training and education for health care workers and social mobilization was frequently noted. There was evidence in high-income countries that new vaccine introduction was associated with reduced health-care costs. Future evaluations of new vaccine introductions should include the systematic and objective assessment of the impacts on a country's immunization system and broader health system, especially in lower-income countries.

The continuing role of Haemophilus influenzae type b carriage surveillance as a mechanism for early detection of invasive disease activity

Prior to the introduction of Haemophilus influenzae type b (Hib) conjugate vaccines, Hib was the leading cause of bacterial meningitis in children under five years of age worldwide. In countries that have adopted Hib vaccination schedules, invasive disease has reduced markedly. Oro-naso pharyngeal carriage is recognized as the most significant source of infection. Hib carriage is significantly associated with poverty, such as overcrowding, poor ventilation in houses, lack of running water, and high smoking rates. Additionally, many Indigenous minority groups report high rates of Hib carriage. A resurgence of Hib disease among Alaskan children in the 1990s, lead to a change in approach to eliminate Hib disease and carriage in high-risk populations. This new approach identifies strategies for eliminating Hib disease focusing on the reservoirs of colonization within families and communities. Monitoring Hib carriage continues to offer an early warning system, whereby intervention could prevent invasive disease resurgence.

Methodology and measurement of the effectiveness of Haemophilus influenzae type b vaccine: systematic review

The use of the highly effective Haemophilus influenzae type b (Hib) conjugate vaccine has increased globally. We review the benefits and limitations of studies measuring Hib vaccine effectiveness (VE). We critically examine the case-control approach by assessing the similarities and differences in methodology and findings and discuss the need for future Hib VE studies. In the absence of good surveillance data, vaccine effectiveness studies can play an important role, particularly with the increasing use of pneumococcal vaccine that has not been well tested under field conditions in less developed countries. However, the effectiveness of Hib vaccine has been well documented so the need for future VE Hib studies is minimal.

Infection is the major component of the disease burden in aboriginal and non-aboriginal Australian children: a population-based study

BACKGROUND

Infection accounts for the majority of pediatric mortality and morbidity in developing countries, but there are limited data on the infectious diseases burden in children from developed countries. We investigated reasons for hospitalization before age 2 years in a birth cohort of Western Australian Aboriginal and non-Aboriginal children.

METHODS

Data on live births between January 1990 and December 2000, and corresponding deaths and hospitalizations in the first 2 years of life, were obtained through linked population-based data.

RESULTS

Almost half the cohort of 270,068 children were hospitalized at least once. Aboriginal children had significantly higher admission rates (2196 vs. 779 per 1000 live births), stayed longer and were more likely to die in hospital than non-Aboriginal children. Infections (mainly respiratory and gastrointestinal) were the most common reason for hospitalization, accounting for 34% of all admissions, with higher rates in Aboriginal (1114 per 1000 live births) than non-Aboriginal children (242 per 1000) (P < 0.001). Over time, admission rates for infections declined in Aboriginal children but increased in non-Aboriginal children. Aboriginal children were admitted 14 times more often for pneumonia than non-Aboriginal children.

CONCLUSIONS

Infections are the leading cause of hospitalization in children under 2 years of age. The continuing heavy burden of serious infections, borne disproportionately by Aboriginal children, needs to be alleviated. Public health interventions such as the development and universal implementation of vaccines for respiratory syncytial virus, rotavirus and influenza are needed, while adequate funding must be committed to Indigenous health services and training.

Case for mandatory fortification of food with folate in Australia, for the prevention of neural tube defects

BACKGROUND

Since the publication of randomized controlled trials demonstrating the prevention of neural tube defects (NTDs) with periconceptional folate, several Australian states have promoted an increase in periconceptional use of folic acid supplements. Since 1996, voluntary fortification of food with folate has been allowed in Australia and New Zealand for the purpose of preventing NTDs.

METHODS

For this report, we synthesized published and unpublished data on folic acid supplement use, voluntary fortification, and trends in NTDs.

RESULTS

There has been an increase in the proportion of women (up to 30-40%) taking periconceptional folic acid supplements in Australia, and many foods (mainly breakfast cereals) are fortified. Supplement use is strongly correlated with educational and socioeconomic status; consumption of voluntarily fortified foods is not. There has been a fall in NTDs of about 30% in the non-Aboriginal population, but no change has been seen in the Aboriginal population.

CONCLUSIONS

These data support mandatory fortification of food as a more equitable approach to achieving sufficient folate intake in the periconceptional period for all women in Australia and New Zealand to prevent the majority of NTDs in their offspring. In May 2004, based on these and other considerations, the Australia and New Zealand Food Regulation Ministerial Council agreed that mandatory fortification of food with folate should be considered as a priority.

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.

Safety and reactogenicity of a novel DTPa-HBV-IPV combined vaccine given along with commercial Hib vaccines in comparison with separate concomitant administration of DTPa, Hib, and OPV vaccines in infants

OBJECTIVE

Combination vaccines simplify vaccine administration and have the potential to promote compliance and cost-effectiveness by decreasing the number of injections needed to immunize a child. The objective of this study was to assess the safety and reactogenicity of the diphtheria-tetanus toxoid-acellular pertussis-hepatitis B virus-inactivated polio virus (DTPa-HBV-IPV) vaccine when coadministered with different Haemophilus influenzae type B (Hib) vaccines in comparison with separate, commercially available, control vaccines in a 3-dose primary vaccination series.

METHODS

An open-label, randomized, parallel-group study in 5318 infants who were 8 to 16 weeks of age at enrollment was conducted in 90 centers in Germany. The incidence of adverse events that occurred in infants who received the DTPa-HBV-IPV candidate vaccine coadministered with 1 of 4 different Hib vaccines (given in separate sites; groups 1-4) was compared with the incidence that occurred in infants who received commercially available control vaccines (DTPa, Hib, and oral polio virus [OPV] vaccine; group 5) administered separately. The vaccines were given as a 3-dose primary series at 3, 4, and 5 months of age. Infants were assessed for solicited local and general adverse events for 4 days and for unsolicited adverse events for 30 days after each vaccine dose. The primary endpoint was to rule out a 7.5% increase in infants who experienced grade 3 (defined as preventing normal everyday activities unless otherwise specified) solicited local and general adverse events over the 3-dose primary course after the combined DTPa-HBV-IPV vaccine coadministered with Hib as compared with commercially available vaccines.

RESULTS

During the 3-dose primary course, 490 of 3029 infants (16.2%) in the pooled DTPa-HBV-IPV vaccine groups and 151 of 744 (20.3%) in the control vaccine group experienced a grade 3 adverse event (rate difference [control minus combination] 4.1%; 90% confidence interval, 1.41-7.13). The lower limit of the 90% confidence interval of the observed difference remained above the prespecified -7.5% limit for noninferiority, thereby meeting the primary endpoint. The incidences of local injection-site reactions were similar for the DTPa-HBV-IPV and DTPa injection sites. Significant differences in the incidence of both local and general adverse events were observed depending on which of the Hib vaccines was coadministered. Infants who received Hib N meningitidis outer-membrane complex protein conjugate vaccine had greater incidences of fever and, to a lesser extent, greater reactions at the Hib injection site than did infants who received other Hib vaccines.

CONCLUSIONS

The combination DTPa-HBV-IPV vaccine administered concomitantly with Hib vaccine at separate sites was at least as safe as coadministration of individual DTPa, Hib, and OPV vaccines in terms of the defined endpoints for safety.

Differing serologic responses to an haemophilus influenzae type b polysaccharide-neisseria meningitidis outer membrane protein conjugate (PRP-OMPC) vaccine in australian aboriginal and caucasian infants - implications for disease epidemiology

This study compared Hib antibody responses to a single lot of PRP-OMPC vaccine given at 2, 4 and 12 months to 57 Aboriginal infants in rural areas of the Northern Territory and 56 Caucasian infants in Sydney, Australia. The Aboriginal infants had lower levels of antibody in cord blood (P>0.05), which were significantly lower (P<0.02) by 2 months of age. Antibody responses to one or two doses of vaccine, measured at 4 and 12 months of age, were similar but the geometric mean titre following the booster dose in Aboriginal infants was significantly lower (1.98 vs. 6.04 mcg/ml, P = 0.002). Low preimmunisation antibody is consistent with the early onset of Hib disease in Aboriginal infants before immunisation. Lower responses to boosting could correlate with persistence of Hib colonisation in indigenous populations.