Protection provided by Haemophilus influenzae type b conjugate vaccines in Los Angeles County: a case-control study

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.

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.

Microbiology and management of joint and bone infections due to anaerobic bacteria

PURPOSE

To describes the microbiology, diagnosis, and management of septic arthritis and osteomyelitis due to anaerobic bacteria.

RESULTS

The predominant anaerobes in arthritis are anaerobic Gram-negative bacilli (AGNB) including the Bacteroides fragilis group, Fusobacterium spp., Peptostreptococcus spp., and Propionibacterium acnes. Infection with P. acnes is associated with a prosthetic joint, previous surgery, and trauma. B. fragilis group is associated with distant infection, Clostridium spp. with trauma, and Fusobacterium spp. with oropharyngeal infection. Most cases of anaerobic arthritis, in contrast to anaerobic osteomyelitis, involved a single isolate, and most cases are secondary to hematogenous spread. The predominant anaerobes in osteomyelitis are Bacteroides, Peptostreptococcus, Fusobacterium, and Clostridium spp. as well as P. acnes. Conditions predisposing to bone infections are vascular disease, bites, contiguous infection, peripheral neuropathy, hematogenous spread, and trauma. Pigmented Prevotella and Porphyromonas spp. are mostly isolated in skull and bite infections, members of the B. fragilis group in hand and feet infections, and Fusobacterium spp. in skull, bite, and hematogenous long bone infections. Many patients with osteomyelitis due to anaerobic bacteria have evidence of an anaerobic infection elsewhere in the body that is the source of the organisms involved in the osteomyelitis. Treatment of arthritis and osteomyelitis involving anaerobic bacteria includes symptomatic therapy, immobilization in some cases, adequate drainage of purulent material, and antibiotic therapy effective against these organisms.

CONCLUSIONS

Anaerobic bacteria can cause septic arthritis and osteomyelitis. Correct diagnosis and appropriate therapy are important contributor to successful outcome.

Bacterial meningitis in childhood at the Children's Hospital of Pittsburgh: 1988-1998

Bacterial meningitis is an important acute infectious disease of childhood that remains a source of substantial morbidity and mortality. The impact of the Haemophilus influenzae type b (HIB) conjugate vaccines on the epidemiology of the other bacterial causes of meningitis in childhood has received little attention. The objective of this study is to report the experience at a tertiary-care children's hospital with the occurrence of bacterial meningitis before and after the licensure of the HIB conjugate vaccine. With use of International Classification of Diseases diagnostic codes for bacterial meningitis, a list of all children admitted to Children's Hospital of Pittsburgh with a primary or secondary diagnosis of meningitis due to H. influenzae, Streptococcus pneumoniae, and Neisseria meningitidis from January 1, 1988, to December 31, 1998, was constructed. Medical records were examined for basic patient demographic information including age, gender, race, bacterial etiology of meningitis, receipt of vaccine for HIB, underlying conditions, and fatalities. Two hundred twenty-one cases of bacterial meningitis caused by H. influenzae, N. meningitidis, and S. pneumoniae were identified. The age of infected children ranged from 1 month to 18 years, with a mean and median age of 38.1 months and 13 months, respectively. Fifty-two percent of the children were female, 83% were Caucasian and 16% were African-American. Before the routine use of HIB conjugate vaccine, HIB was the bacterial species responsible for the greatest proportion of cases (average of 58%/year). The absolute number of cases of bacterial meningitis attributable to HIB declined after 1991 to an average of 2.5 cases/year. The number of cases of meningitis caused by S. pneumoniae and N. meningitidis have remained relatively stable between 1988 and 1998. The case fatality rates for children with meningitis caused by H. influenzae, S. pneumoniae, and N. meningitidis were 0.0%, 9.2%, and 7.5%, respectively. Most cases of meningitis due to HIB occurred in children who had not been immunized. Three children who received the polysaccharide vaccine developed meningitis due to HIB; there were no failures of the conjugate vaccine.

Haemophilus influenza type b vaccine in Israel: experience in a paediatric ambulatory clinic

In Israel, vaccination are the overall responsibility of the government. We were the first in Israel to give the Hib (Haemophilus influenza type b) vaccine to the population, through independent means, without government control. The aim of the study was to follow longitudinally the specific group of children vaccinated in our ambulatory clinic. In this study, 1,497 children between 2 and 52 [mean (SD) 13 (9)] months of age at the time of first vaccination were vaccinated with Hib vaccine. Over the next 7 years, they were followed up by repeated phone calls when parents were asked about hospitalisation and any serious infectious diseases. Of the 1,497, 1,444 were followed during the years 1992 to 1999 and 36 were hospitalised during this time. All blood and cerebrospinal fluid cultures were negative. No proven case of Hib infection could be demonstrated. Despite the small sample size, this study justifies the continued use of the vaccine along with maintaining surveillance for Hib infection.

Worldwide Haemophilus influenzae type b disease at the beginning of the 21st century: global analysis of the disease burden 25 years after the use of the polysaccharide vaccine and a decade after the advent of conjugates

Vaccination against Haemophilus influenzae type b (Hib) diseases began a quarter of a century ago with a polysaccharide vaccine; this vaccine was followed by four different conjugates 10 years later. In this review, the burden of global Hib disease is quantified following this 25-year period of vaccine availability to determine the potential impact of conjugate vaccines. This task was accomplished by analysis of data available in 10 languages in 75 geographical regions of over 50 countries. All severe Hib diseases, not only meningitis, were characterized, and special attention was paid to the most vulnerable age group, i.e., children aged 0 to 4 years. Prior to vaccination, the weighted worldwide incidence of meningitis in patients younger than 5 years was 57/100,000, and for all Hib diseases except nonbacteremic pneumonia, it was 71/100,000, indicating 357,000 and 445,000 cases per year, respectively. At least 108,500 of these children died. For all age groups combined, there were 486,000 cases of Hib disease, excluding pneumonia, with 114,200 deaths and probably an equal number of sequelae per annum. If the figures for nonbacteremic pneumonia are included, a conservative estimate is that over 2.2 million cases of infection and 520,000 deaths from Hib disease occurred worldwide, but the true numbers might have been greater. Despite these large numbers and availability of safe and efficacious vaccines, only 38,000 cases annually are prevented-a meager 8% or less than a 2% reduction in cases, depending on whether nonbacteremic pneumonia is included in the calculations. Although vaccination has had great success in some affluent countries, the current level of activity has had a very small impact globally. The use of conjugates, preferably with a reduced number of doses and in combination with other vaccines or perhaps in fractional doses, should be extended to less privileged countries, where most Hib disease occurs.

Worldwide Haemophilus influenzae type b disease at the beginning of the 21st century: global analysis of the disease burden 25 years after the use of the polysaccharide vaccine and a decade after the advent of conjugates

Vaccination against Haemophilus influenzae type b (Hib) diseases began a quarter of a century ago with a polysaccharide vaccine; this vaccine was followed by four different conjugates 10 years later. In this review, the burden of global Hib disease is quantified following this 25-year period of vaccine availability to determine the potential impact of conjugate vaccines. This task was accomplished by analysis of data available in 10 languages in 75 geographical regions of over 50 countries. All severe Hib diseases, not only meningitis, were characterized, and special attention was paid to the most vulnerable age group, i.e., children aged 0 to 4 years. Prior to vaccination, the weighted worldwide incidence of meningitis in patients younger than 5 years was 57/100,000, and for all Hib diseases except nonbacteremic pneumonia, it was 71/100,000, indicating 357,000 and 445,000 cases per year, respectively. At least 108,500 of these children died. For all age groups combined, there were 486,000 cases of Hib disease, excluding pneumonia, with 114,200 deaths and probably an equal number of sequelae per annum. If the figures for nonbacteremic pneumonia are included, a conservative estimate is that over 2.2 million cases of infection and 520,000 deaths from Hib disease occurred worldwide, but the true numbers might have been greater. Despite these large numbers and availability of safe and efficacious vaccines, only 38,000 cases annually are prevented-a meager 8% or less than a 2% reduction in cases, depending on whether nonbacteremic pneumonia is included in the calculations. Although vaccination has had great success in some affluent countries, the current level of activity has had a very small impact globally. The use of conjugates, preferably with a reduced number of doses and in combination with other vaccines or perhaps in fractional doses, should be extended to less privileged countries, where most Hib disease occurs.

Combined vaccination of Haemophilus influenzae type b conjugate and diphtheria-tetanus-pertussis containing acellular pertussis

After the introduction of effective Haemophilus influenzae type b (Hib) conjugate vaccines, clinical practice has driven the development of combination vaccines comprising Hib conjugates with the infant diphtheria-tetanus-pertussis (DTP) vaccines. However, when such combinations contain an acellular pertussis component (Pa), the antibody response to Hib is lower than that with separate injections and doubts have been raised about their efficacy. We believe that such concerns are unwarranted, since the serological correlates of efficacy previously applied for Hib polysaccharide vaccines seem inappropriate for Hib conjugates. Furthermore, our own studies have shown that the lower antibody responses are not associated with impaired function of the antibodies induced, nor, and possibly more importantly, with the induction of immune memory against Hib. Therefore, with the proviso that careful clinical surveillance of Hib disease is maintained, we encourage the introduction of DTPa-Hib combinations to facilitate the inclusion of Hib into the already crowded childhood immunisation schedule.

Genetically derived toxoids for use as vaccines and adjuvants

Until very recently, development of vaccines has been based on an empirical approach. For example, bacterial toxins have been detoxified using empirical chemical treatment. Progress in biotechnology and molecular biology has allowed the fine knowledge of the structure-function relationship of several bacterial toxins. Thanks to this, the genetic attenuation of bacterial toxins has been made possible. Following this approach, a genetically detoxified pertussis toxin has been produced. This molecule is now the component of an acellular pertussis vaccine, which has been shown to be highly immunogenic and efficacious in infants. The same strategy of molecular detoxification of bacterial toxins has been applied to cholera toxin and to the Escherichia coli heat-labile enterotoxin. Toxin mutants devoid of any toxic activity have been produced and shown in animals to be highly immunogenic and to exhibit strong adjuvanticity when administered at mucosal sites in conjunction with several antigens. These successful results show that rational design of stronger and safer vaccines is feasible.

Efficacy of Haemophilus influenzae type b conjugate vaccines and persistence of disease in disadvantaged populations. The Haemophilus Influenzae Study Group

OBJECTIVES

The purpose of this study was to evaluate the effectiveness of Haemophilus influenzae type b (Hib) conjugate vaccines among children aged 2 to 18 months and to determine risk factors for invasive Hib disease during a period of declining incidence (1991-1994).

METHODS

A prospective population-based case-control study was conducted in a multistate US population of 15.5 million. A laboratory-based active surveillance system was used for case detection.

RESULTS

In a multivariate analysis, having a single-parent mother (odds ratio [OR] = 4.3, 95% confidence interval [CI] = 1.2, 14.8) and household crowding (OR = 3.5, 95% CI = 1.03, 11.7) were risk factors for Hib disease independent of vaccination status. After adjustment for these risk factors, the protective efficacy of 2 or more Hib vaccine doses was 86% (95% CI = 16%, 98%). Among undervaccinated subjects, living with a smoker (P = .02) and several indicators of lower socioeconomic status were risk factors for Hib disease.

CONCLUSIONS

Hib disease still occurs at low levels in the United States, predominantly in socioeconomically disadvantaged populations. Low immunization coverage may facilitate continuing transmission of Hib. Special efforts to achieve complete and timely immunization in disadvantaged populations are needed.

Haemophilus influenzae type b conjugate vaccines: a review of efficacy data

BACKGROUND

The development of a vaccine against Haemophilus influenzae type b (Hib) was stimulated by its recognition as a major pathogen of early childhood. The first vaccine to be developed was composed of the capsular polysaccharide of the organism, polyribosylribitol phosphate (PRP), and although effective in older children, it failed to protect those <2 years of age, the group with the highest burden of disease. The conjugation of PRP to protein led to a group of vaccines with enhanced immunogenicity and the ability to induce immunologic memory and thus the potential to protect in infancy.

OBJECTIVES

To review the trials of Hib conjugate vaccines in which protective efficacy in infants has been assessed and the experience in countries in which Hib conjugate vaccines have been introduced into the routine infant immunization schedule.

DISCUSSION

Each of the Hib conjugate vaccines [PRP-diphtheria toxoid conjugate (PRP-D), PRP conjugated to outer membrane protein of Neisseria meningitidis group B (PRP-OMP), PRP oligosaccharides conjugated to mutant diphtheria toxin CRM197, (HbOC) and PRP conjugated to tetanus toxoid (PRP-T)] has been subjected to prospective clinical trials and all have demonstrated high protective efficacy with one exception: that of the least immunogenic vaccine, PRP-D, when used in a Native American population with a high level of natural disease. The trials have used different populations and different schedules, which limits conclusions about relative efficacies. However, it seems likely that all the vaccines are capable of high efficacy in populations with low levels and late age of Hib disease. Three vaccines (PRP-D, PRP-OMP, PRP-T) have been tested in populations with high rates of disease and only PRP-D has been found lacking. As predicted by immunogenicity data, PRP-OMP affords efficacy after one dose, and PRP-T is efficacious with an accelerated schedule. Of more practical significance the effectiveness of these vaccines when introduced into populations has been uniformly impressive.

CONCLUSIONS

Particularly where vaccine coverage is high, it is now likely that Hib disease can be eliminated using Hib conjugate vaccines in infancy.

Molecular basis of vaccination

Vaccines represent the most cost-effective means to prevent infectious diseases. Most of the vaccines which are currently available were developed long before the era of molecular biology and biotechnology. They were obtained following empirical approaches leading to the inactivation or to the attenuation of microorganisms, without any knowledge neither of the mechanisms of pathogenesis of the disease they were expected to protect from, nor of the immune responses elicited by the infectious agents or by the vaccine itself. The past two decades have seen an impressive progress in the field of immunology and molecular biology, which have allowed a better understanding of the interactions occurring between microbes and their hosts. This basic knowledge has represented an impetus towards the generation of better vaccines and the development of new vaccines. In this monograph we briefly summarize some of the most important biotechnological approaches that are currently followed in the development of new vaccines, and provide details on an approach to vaccine development: the genetic detoxification of bacterial toxins. Such an approach has been particularly successful in the rational design of a new vaccine against pertussis, which has been shown to be extremely efficacious and safe. It has been applied to the construction of powerful mucosal adjuvants, for administration of vaccines at mucosal surfaces.

Arthroscopically assisted treatment of acute septic knees in infants using the Micro-Joint Arthroscope

Five infants with an acute hematogenous septic arthritis of the knee were treated with arthroscopically assisted drainage using the Micro-Joint Arthroscope (MJA; Linvatec, Largo, FL) combined with antibiotic therapy and early postoperative motion. The average patient age was 16 months (range, 4 to 24 months). No surgical or anesthetic complications occurred. All knees were clinically and radiologically normal at an average follow-up of 26 months.