Long-term persistence of immunity after immunisation with Haemophilus influenzae type b conjugate vaccine

Relationship between T-cell-dependent and T-cell-independent vaccines after neurotrauma; is the B-cell response preserved?

Background

After trauma and central nervous system (CNS) injury, trauma-induced immune deficiency syndrome (TIDS) and CNS injury-induced immune deficiency syndrome (CIDS) may negatively affect responses to T-cell-dependent vaccines, such as pneumococcal conjugate vaccine (PCV) recommended after basilar fracture. This study (NCT02806284) aimed to investigate whether there after neurotrauma is a correlation between T-cell-dependent and independent vaccine responses and, thus, if B-cell activity is similarly depressed and whether the T-cell-dependent response is possible to predict.

Methods

Adult patients with basilar fracture (n = 33) and those undergoing pituitary gland surgery (n = 23) were within 10 days vaccinated with a T-cell-dependent vaccine against Haemophilus influenzae type b (Hib) and a T-cell-independent pneumococcal polysaccharide vaccine (PPSV). Samples reflecting the systemic inflammatory response and pre- and post-vaccination antibody levels after 3–6 weeks against Hib and PPSV were collected and determined by enzyme immunoassays.

Results

High and significant correlations were detected in the responses to different pneumococcal serotypes, but none between the Hib and PPSV responses. No differences in trauma scores, C-reactive protein, IL-6, IL-10, pentraxin 3, fractalkine or calprotectin plasma concentrations or in ex vivo TNF-α, IL-6 or IL-10 responses to endotoxin were found between Hib vaccination responders and non-responders.

Conclusions

There was no correlation between the pneumococcal responses and that to Hib, indicating that B-cell function is not similarly depressed as T-cell function. Grading of the trauma or parameters reflecting the innate immune response could not predict the T-cell-dependent vaccine response. There is a need of further studies evaluating the vaccine response after neurotrauma.

Yin and yang of immunological memory in controlling infections: Overriding self defence mechanisms

Immunological memory is critical for host immunity and decisive for individual to respond exponentially to previously encountered infection. Both T and B cell memory are known to orchestrate immunological memory with their central and effector memory arms contributing in prolonged immunity/defence mechanisms of host. While central memory helps in maintaining prolonged immunity for a particular infection, effector memory helps in keeping local/seasonal infection in control. In addition to this, generation of long-lived plasma cells is pivotal for generating neutralizing antibodies which can enhance recall and B cell memory to control re-infection. In view of this, scaling up memory response is one of the major objectives for the expected outcome of vaccination. In this line, this review deals with the significance of memory cells, molecular pathways of their development, maintenance, epigenetic regulation and negative regulation in various infections. We have also highlighted the significance of both T and B cell memory responses in the vaccination approaches against range of infections which is not fully explored so far.[Box: see text].

Protection Against Invasive Infections in Children Caused by Encapsulated Bacteria

The encapsulated bacteria Streptococcus pneumoniae, Neisseria meningitis, Haemophilus influenzae, and Streptococcus agalactiae (Group B Streptococcus) have been responsible for the majority of severe infections in children for decades, specifically bacteremia and meningitis. Isolates which cause invasive disease are usually surrounded by a polysaccharide capsule, which is a major virulence factor and the key antigen in protective protein-polysaccharide conjugate vaccines. Protection against these bacteria is largely mediated via polysaccharide-specific antibody and complement, although the contribution of these and other components, and the precise mechanisms, vary between species and include opsonophagocytosis and complement-dependent bacteriolysis. Further studies are required to more precisely elucidate mechanisms of protection against non-type b H. influenzae and Group B Streptococcus.

Lower response to early T-cell-dependent vaccination after neurotrauma or neurosurgery in adults

BACKGROUND

Recent international guidelines recommend vaccination with a 13-valent pneumococcal conjugate vaccine to reduce the risk of meningitis after neurotrauma with cerebrospinal fluid leak. The antibody response and optimal time point for vaccination have not been established and because the risk of meningitis is at the highest shortly after trauma, early vaccination is preferable. This study aimed to investigate the antibody response and to ensure that central nervous system injury-induced immunodepression did not affect the response to a T-cell-dependent conjugate vaccine when administered shortly after the injury.

METHODS

So as not to interfere with routine pneumococcal vaccination, a conjugate vaccine against Haemophilus influenza type b (Hib) was chosen for the study. Thirty-three patients with basilar skull fracture and 23 patients undergoing transsphenoidal pituitary gland surgery were vaccinated within 10 days after trauma/surgery and 29 control patients at least three weeks after trauma/surgery. Sera were collected pre- and post-vaccination for analysis of anti-Hib concentration.

RESULTS

Four patients with post-vaccination target antibody concentration before vaccination were excluded from analysis. In the neurotrauma and neurosurgery groups 10/32 (31%) and 5/20 (25%) patients, respectively, were non-responders compared with 3/29 (10%) in the control group. Log10 anti-Hib concentrations in the neurotrauma, neurosurgery and control groups were 1.52 ± 0.15, 1.38 ± 0.15 and 1.81 ± 0.12 μg/ml, respectively.

CONCLUSIONS

The majority of the patients responded to vaccination. However, the number of responders was significantly decreased and antibody concentration significantly lower in patients vaccinated early after the trauma/surgery. Investigation of the pneumococcal conjugate vaccine response in neurotrauma patients is therefore urgent.

Prevention ofHaemophilus influenzaetype b disease: past success and future challenges

Haemophilus influenzae type b (Hib) is responsible for significant morbidity and mortality worldwide, particularly in children under 5 years of age. In countries where the Hib conjugate vaccine is not routinely used, Hib is a leading cause of childhood pneumonia and meningitis. Routine use of the Hib conjugate vaccines has resulted in a remarkable decline in Hib disease in developed and developing countries. However, Hib conjugate vaccines are not routinely available in most developing countries, many of which have high burdens of Hib disease. This review outlines the pathogenesis and epidemiology of Hib disease, and the various options for prevention.

Long-term persistence of immunity and B-cell memory following Haemophilus influenzae type B conjugate vaccination in early childhood and response to booster

BACKGROUND

Protection against Haemophilus influenzae type b (Hib), a rapidly invading encapsulated bacteria, is dependent on maintenance of an adequate level of serum antibody through early childhood. In many countries, Hib vaccine booster doses have been implemented after infant immunization to sustain immunity. We investigated the long-term persistence of antibody and immunological memory in primary-school children following infant (with or without booster) Hib vaccination.

METHODS

Anti-polyribosylribitol phosphate (PRP) immunoglobulin G (IgG) concentration and the frequency of circulating Hib-specific memory B cells were measured before a booster of a Hib-serogroup C meningococcal (MenC) conjugate vaccine and again 1 week, 1 month, and 1 year after the booster in 250 healthy children aged 6-12 years in an open-label phase 4 clinical study.

RESULTS

Six to 12 years following infant priming with 3 doses of Hib conjugate vaccine, anti-PRP IgG geometric mean concentrations were 3.11 µg/mL and 0.71 µg/mL and proportions with anti-PRP IgG ≥1.0 µg/mL were 79% and 43% in children who had or had not, respectively, received a fourth Hib conjugate vaccine dose (mean age, 3.9 years). Higher baseline and post-Hib-MenC booster responses (anti-PRP IgG and memory B cells) were found in younger children and in those who had received a fourth Hib dose.

CONCLUSIONS

Sustained Hib conjugate vaccine-induced immunity in children is dependent on time since infant priming and receipt of a booster. Understanding the relationship between humoral and cellular immunity following immunization with conjugate vaccines may direct vaccine design and boosting strategies to sustain individual and population immunity against encapsulated bacteria in early childhood. Clinical Trials Registration ISRCTN728588998.

Two decades of experience with the Haemophilus influenzae serotype b conjugate vaccine in the United Kingdom

BACKGROUND

The Haemophilus influenzae serotype b (Hib) conjugate vaccine was introduced into the UK national childhood immunization program in 1992 after clinical trials reported the vaccine to be highly immunogenic in infants as young as two months of age.

OBJECTIVE

The goal of this study was to describe and comment on the impact of routine Hib immunization on the epidemiology of invasive Hib disease in the United Kingdom. In addition, the development of Hib polysaccharide and conjugate vaccines was reviewed.

METHODS

A literature search was conducted of PubMed for invasive Hib disease epidemiology in the United Kingdom. The UK Health Protection Agency Web site was also searched for relevant publications.

RESULTS

The incidence of invasive Hib incidence in children aged <5 years fell from 21/100,000 to 44/100,000 in the prevaccine era to 0.63/100,000 in 1998, with an estimated vaccine failure rate of 2.2/100,000 vaccinees. After 1999, however, invasive Hib disease increased, particularly in toddlers, and peaked in 2003. Potential reasons for the resurgence included a greater-than-expected decline in Hib antibodies after primary immunization, waning of herd immunity offered by the initial catch-up campaign, and use of a less immunogenic Hib combination vaccine containing acellular pertussis in 2000-2001. In response to the resurgence, a Hib combination vaccine containing whole-cell pertussis was reintroduced in 2002, followed by a childhood Hib booster campaign in 2003. In 2004, the recommended infant vaccine was changed to a different Hib/acellular pertussis combination vaccine containing inactivated polio, which had a satisfactory Hib response, was less reactogenic, and eliminated the risk of vaccine-associated paralytic poliomyelitis. This action was followed by introduction of a routine 12-month Hib booster in 2006. Together, these measures led to a decline in invasive Hib disease across all age groups. In 2010, there were only 30 invasive Hib cases, with 6 reported in children aged <5 years and no deaths in this age group since 2007.

CONCLUSIONS

Control of Hib disease is currently the best that has been achieved since the introduction of the routine Hib vaccination almost 20 years ago.

Understanding and Governing Public Health Risks by Modeling

Increase in the use and development of computational tools to govern public health risks invites us to study their benefits and limitations. To analyze how risk is perceived and expressed through these tools is relevant to risk theory. This chapter clarifies the different concepts of risk, contrasting especially the mathematically expressed ones with culturally informed notions, which address a broader view on risk. I will suggest that a fruitful way to contextualize computational tools, such mathematical models in risk assessment is “analytics of risk,” which ties together the technological, epistemological, and political dimensions of the process of governance of risk. I will clarify the development of mathematical modeling techniques through their use in infectious disease epidemiology. Epidemiological modeling functions as a form of “risk calculation,” which provides predictions of the infectious outbreak in question. These calculations help direct and design preventive actions toward the health outcomes of populations. This chapter analyzes two cases in which modeling methods are used for explanation-based and scenario-building predictions in order to anticipate the risks of infections caused by Haemophilus influenzae type b bacteria and A(H1N1) pandemic influenza virus. I will address an interesting tension that arises when model-based estimates exemplify the population-level reasoning of public health risks but has restricted capacity to address risks on individual level. Analyzing this tension will lead to a fuller account to understand the benefits and limitations of computational tools in the governance of public health risks.

Antibody response to Haemophilus influenzae type-b conjugate vaccine in children and young adults with congenital asplenia or after undergoing splenectomy

Absence of the spleen constitutes a risk of infection caused by encapsulated bacteria. The aim of our study was to determine the immune response to Haemophilus influenzae type-b (Hib) conjugate vaccine (HibCV) in asplenic individuals, considering the cause of asplenia, the age when splenectomy was carried out, and previous Hib vaccinations. Twenty asplenic patients, aged five to 25 years, were immunized with a single dose of HibCV. The specific antibody concentrations against HibCV were measured by enzyme-linked immunosorbent assay. Before vaccinations, the geometric mean antibody concentration (GMC) had an average value of 3.21 μg/ml and was comparable for all of the patients, regardless of the causes of asplenia. After vaccinations, the GMC was significantly higher, with an average of 6.78 μg/ml. Further, 4.5 years after vaccinations, the GMC was comparable to that of previously unvaccinated children. Moreover, 17/20 patients had GMC ≥ 1.0 μg/ml, which included all of the children with congenital asplenia, children splenectomized before the age of six years, and only 57% of children splenectomized after that age. HibCV gives asplenic patients long-term protection. Hence, HibCV should be administered regardless of previous vaccinations and time from splenectomy, even if antibody evaluation is not available.

Foresight in medicine: current challenges with Haemophilus influenzae type b conjugate vaccines

An effective vaccine to prevent invasive infections caused by Haemophilus influenzae type b (Hib) bacteria has been available for more than 20 years. Hib conjugate vaccine is safe, efficacious and easy to use, and its cost-benefit ratio is high both in industrialized as well as in developing countries. In spite of this, WHO estimates that every year approximately 8 million children contract life-threatening Haemophilus infections, especially meningitis or severe pneumonia. If we want to take seriously the Millenium Development Goal of reducing the mortality of under 5-year-old children by two-thirds before the year 2015, an effective means to contribute to this would be more efficient use of Hib vaccines.

Immunogenicity of Haemophilus influenzae type b conjugate vaccines in Korean infants: a meta-analysis

A meta-analysis was performed on the immunogenicity of Haemophilus influenzae type b (Hib) conjugate vaccines after 2 (2 and 4 months) and 3 doses (2, 4, and 6 months) in Korean infants. A database search of MEDLINE, KoreaMed, and Korean Medical Database was done. The primary outcome measure was the proportion of infants with anti-polyribosylribitol phosphate (PRP) concentrations > or =1.0 microg/mL. Eight studies including eleven trials were retrieved. One trial reported on the diphtheria toxoid conjugate vaccine (PRP-D) and 2 trials each on the mutant diphtheria toxin (PRP-CRM) and Neisseria meningitidis outer-membrane protein (PRP-OMP) conjugate vaccine. Heterogeneity in study designs between trials on PRP-CRM was noted and one trial reported on a monovalent and another on a combination PRP-OMP vaccine. Thus, a meta-analysis was conducted only on the tetanus toxoid conjugate vaccine (PRP-T). After a primary series of 2 doses and 3 doses, 80.6% (95% confidence interval [CI]; 76.0-85.1%) and 95.7% (95% CI; 94.0-98.0%) of infants achieved an antibody level > or =1.0 microg/mL, respectively. The immunogenic response to the PRP-T vaccine was acceptable after a primary series of 3 doses and also 2 doses. A reduced number of doses as a primary series could be carefully considered in Korean infants.

Immunoglobulin G avidities in infants in Mexico after primary immunization with three doses of polyribosylribitol phosphate-tetanus toxoid Haemophilus influenzae type b vaccine

Serum immunoglobulin G concentrations and avidities specific to Haemophilus influenzae type b (Hib) were measured in 208 children living in Guadalajara and Mexico City. Protective concentrations were found in 98.9% and 100.0% of participants, respectively. Geometric mean concentrations differed between both populations and/or among age groups. Mean avidities differed only among the 7- to 12-month-old children. Diphtheria-tetanus-whole-cell pertussis-hepatitis B-Hib primary vaccination seems to induce protection in Mexican children.

Effects of feeding probiotics during weaning on infections and antibody responses to diphtheria, tetanus and Hib vaccines

Microbial exposure is necessary for the development of normal immune function, which has driven the idea of using probiotics for treatment and prevention of immune-mediated diseases in infancy and childhood. Mounting evidence indicates that probiotics have immunomodulatory effects. However, the mechanisms are still poorly understood. Specific antibody response is a valuable proxy for immune system maturation status in infancy. We aimed at determining the impact of Lactobacillus F19 (LF19) during weaning on infections and IgG antibody responses to routine vaccines. In a double-blind, placebo-controlled randomized intervention trial, infants were fed cereals with (n = 89) or without LF19 (n = 90) from 4 to 13 months of age. Infants were immunized with DTaP (diphtheria and tetanus toxoid and acellular pertussis), polio and Hib-conjugate vaccines at (3), 5(1/2) and 12 months of age. We assessed the number of days with infections, antibiotic prescriptions and antibody concentrations to Hib capsular polysaccharide (HibPS), diphtheria toxin (D) and tetanus toxoid (T) before and after the second and third doses. Days with infectious symptoms did not differ between the groups. Days with antibiotic prescriptions were fewer in the LF19 group (p = 0.044). LF19 enhanced anti-D concentrations when adjusting for breastfeeding duration and colonization with LF19 (p = 0.024). There was an interaction of the intervention and colonization with LF19 on anti-T concentrations during the course of vaccination (p = 0.035). The anti-HibPS concentrations were higher after the first and second dose of Hib vaccine in infants breastfed <6 months compared with those breastfed > or =6 months (p < 0.05), with no effect by LF19. In conclusion, feeding LF19 did not prevent infections, but increased the capacity to raise immune responses to protein antigens, with more pronounced effects in infants breastfed <6 months.

Understanding the impact of Hib conjugate vaccine on transmission, immunity and disease in the United Kingdom

A rise in invasive Haemophilus influenzae type b (Hib) infections occurred 8 years after vaccine introduction in the United Kingdom. Aspects of Hib vaccine delivery unique to the United Kingdom have been implicated. The authors developed a fully age-structured deterministic susceptible-infected-resistant-susceptible mathematical model, expressed as a set of partial differential equations, to better understand the causes of declining vaccine effectiveness. We also investigated the consequences of the vaccine's impact on reducing Hib transmission for maintenance of immunity. Our findings emphasized the importance of maintaining high post-immunization antibody titres among age groups at greatest risk of invasive infections. In keeping with UK population-based estimates, low direct efficacy of immunological memory against disease was found, cautioning against over-reliance on evidence of priming alone as a correlate of population protection. The contribution of herd immunity to disease control was reinforced. Possible intervention strategies will be explored in subsequent work.

A randomized study on donor immunization with tetanus–diphtheria, Haemophilus influenzae type b and inactivated poliovirus vaccines to improve the recipient responses to the same vaccines after allogeneic bone marrow transplantation

The HLA-identical sibling donors of 111 bone marrow transplantation (BMT) recipients were randomised to receive or not to receive tetanus-diphtheria (T-d), Haemophilus influenzae type b (Hib), and inactivated poliovirus (IPV) vaccines 2-10 weeks before BM harvest. Fifty-three (DV+ group) recipients received the graft from a vaccinated donor and 58 (DV- group) from an unvaccinated donor. All recipients were vaccinated with the T-d, Hib and IPV vaccines at 3, 6 and 12 months after BMT. Diphtheria and Hib antibody concentrations were consistently higher in the DV+ than in the DV- group from 6 months post transplantation onwards. The differences were significant at 6 and 13 months for diphtheria and at 12 months for Hib antibody concentrations. Tetanus, PV1, PV2 and PV3 antibody levels were similar in both groups. Patients transplanted from donors with high tetanus, diphtheria and Hib antibody concentrations had higher respective antibody concentrations after BMT than those transplanted from donors with low antibody concentrations. Especially patients whose donors have low-specific antibody concentrations may benefit from donor vaccination with protein and conjugate vaccines.

Effect of probiotics on vaccine antibody responses in infancy--a randomized placebo-controlled double-blind trial

Probiotics are immunomodulatory and may thus affect vaccine antibody responses. With the accumulating evidence of their health-promoting effects, probiotics are increasingly administered in allergy-prone infants. Therefore, we studied the effect of probiotics on antibody responses to diphtheria, tetanus and Haemophilus influenzae type b (Hib) vaccines in 6-month-old infants participating in a randomized placebo-controlled double-blind allergy-prevention trial. Mothers of unborn children at increased risk for atopy used a combination of four probiotic strains, or a placebo, for 4 wk before delivery. During 6 months from birth, their infants received the same probiotics and galacto-oligosaccharides, or a placebo. The infants were immunized with a DTwP (diphtheria, tetanus and whole cell pertussis) at ages 3, 4, and 5 months, and with a Hib polysaccharide conjugate at 4 months. Serum diphtheria, tetanus, and Hib IgG antibodies were measured at 6 months. In the probiotic group, protective Hib antibody concentrations (>/=1 microg/ml) occurred more frequently, 16 of 32 (50%) vs. six of 29 (21%) (p = 0.020), and the geometric mean (inter-quartile range) Hib IgG concentration tended to be higher 0.75 (0.15-2.71) microg/ml than in the placebo group 0.40 (0.15-0.92) microg/ml (p = 0.064). In these respective groups, diphtheria, 0.38 (0.14-0.78) vs. 0.47 (0.19-1.40) IU/ml (p = 0.449), and tetanus, 1.01(0.47-1.49) vs. 0.81 (0.56-1.39) IU/ml (p = 0.310), IgG titers were comparable. In conclusion, in allergy-prone infants probiotics seem not to impair antibody responses to diphtheria, tetanus, or Hib, but may improve response to Hib immunization.

Safety and immunogenicity of heptavalent pneumococcal conjugate vaccine booster in taiwanese toddlers

BACKGROUND/PURPOSE

Pneumococcal infection causes high morbidity and mortality in children. Prevention of pneumococcal diseases by effective vaccination is an urgent need. This study evaluated the safety and immunogenicity of heptavalent pneumococcal conjugate (7VPnC) vaccine (serotypes 4, 6B, 9V, 14, 18C, 19F, 23F) booster dose administered at 15-20 months of age in Taiwanese toddlers.

METHODS

Fifty-eight healthy Taiwanese toddlers who were primed with three doses of the 7VPnC vaccine in infancy received a booster dose in an open-label, noncomparative trial. Routine oral polio vaccine and diphtheria toxoid, tetanus toxoid, and pertussis vaccine were administered concomitantly. Surveillance for safety was conducted after vaccination. Antibody concentration to each of the seven pneumococcal serotypes was measured before and 1 month after the booster dose.

RESULTS

Mild to moderate local reactions were common (45-50%). Fever, fussiness, restlessness, and loss of appetite were the most frequent systemic reactions (31-50%). Before the booster dose of vaccine, 68% (for serotype 18C) to 100% (for serotype 14) of subjects had antibody concentrations >or= 0.2 microg/mL to different pneumococcal serotypes. After the booster dose, the geometric mean concentration of IgG increased significantly (p < 0.001) for all seven serotypes indicating the induction of immunologic memories. Ninety-eight percent of the toddlers had antibody concentration >or= 0.2 microg/mL against all serotypes after the booster.

CONCLUSION

The 7VPnC vaccine containing the prevalent serotypes in Taiwan is safe and effective in boosting immunity against pneumococcal disease in Taiwanese children.

Immunogenicity and effectiveness of Haemophilus influenzae type b conjugate vaccine in HIV infected and uninfected African children

The quantitative (anti-Hib capsular polysaccharide antibody concentrations; anti-HibPS) and qualitative (bactericidal activity and avidity) aspects in immune responses to Haemophilus influenzae type b polyribosyl ribitol phospshate-CRM(197) conjugate vaccine (HibCV; HibTiter) were evaluated in 66 HIV infected children not receiving anti-retroviral therapy and 127 HIV uninfected children. Surveillance was conducted for invasive Hib disease in a cohort of 39,865 (approximately 6.4% of whom were HIV infected) children from March 1998 to June 2004. HIV infected children had lower anti-HibPS geometric mean antibody concentrations 1 month post-immunisation than HIV uninfected children (P<0.00001) and were less likely to have anti-HibPS antibody concentrations of >or=1.0 microg/ml (RR 0.54; 95% CI 0.43-0.69). A lower proportion of HIV infected children than HIV uninfected children (RR 0.78; 95% CI 0.66-0.93) had measurable anti-Hib serum bactericidal activity (SBA) and the HibPS antibody concentration required for 50% killing of Hib bacteria was greater among HIV infected than HIV uninfected children (P=0.001). The estimated risk of HibCV failure was 35.1-fold greater (95% CI 14.6-84.6) amongst HIV infected than HIV uninfected children.

Protection by natural human immunoglobulin M antibody to meningococcal serogroup B capsular polysaccharide in the infant rat protection assay is independent of complement-mediated bacterial lysis

Neisseria meningitidis, an important cause of bacterial meningitis and septicemia worldwide, is associated with high mortality and serious sequelae. Natural immunity against meningococcal disease develops with age, but the specificity and functional activity of natural antibodies associated with protection are poorly understood. We addressed this question by using a selected subset of prevaccination sera (n = 26) with convergent or discrepant serum bactericidal activity (SBA) and infant rat protective activity (IRPA) against the serogroup B meningococcal strain 44/76-SL (B:15:P1.7,16) from Icelandic teenagers. The sera were analyzed by opsonophagocytic activity (OPA) assay, immunoblotting, immunoglobulin G (IgG) quantitation against live meningococcal cells by flow cytometry, and enzyme immunosorbent assay (EIA). High levels of SBA and OPA were reflected in distinct IgG binding to major outer membrane proteins and/or lipopolysaccharide in immunoblots. However, we could not detect any specific antibody patterns on blots that could explain IRPA. Only IgM antibody to group B capsular polysaccharide (B-PS), measured by EIA, correlated positively (r = 0.76, P < 0.001) with IRPA. Normal human sera (NHS; n = 20) from healthy Finnish children of different ages (7, 14, and 24 months and 10 years) supported this finding and showed an age-related increase in IRPA that coincided with the acquisition of B-PS specific IgM antibody. The protection was independent of complement-mediated bacterial lysis, as detected by the inability of NHS to augment SBA in the presence of human or infant rat complement and the equal protective activity of NHS in rat strains with fully functional or C6-deficient complement.

Cost-effectiveness of conjugate meningococcal vaccination strategies in the United States

CONTEXT

The US Food and Drug Administration approved a meningococcal conjugate A/C/Y/W-135 vaccine (MCV-4) for use in persons aged 11 to 55 years in January, 2005; licensure for use in younger age groups is expected in 2 to 4 years.

OBJECTIVE

To evaluate and compare the projected health and economic impact of MCV-4 vaccination of US adolescents, toddlers, and infants.

DESIGN

Cost-effectiveness analysis from a societal perspective based on data from Active Bacterial Core Surveillance (ABCs) and other published and unpublished sources. Sensitivity analyses in which key input measures were varied over plausible ranges were performed.

SETTING AND PATIENTS

A hypothetical 2003 US population cohort of children 11 years of age and a 2003 US birth cohort.

INTERVENTIONS

Hypothetical routine vaccination of adolescents (1 dose at 11 years of age), toddlers (1 dose at 1 year of age), and infants (3 doses at 2, 4, and 6 months of age). Each vaccination scenario was compared with a "no-vaccination" scenario.

MAIN OUTCOME MEASURES

Meningococcal cases and deaths prevented, cost per case prevented, cost per life-year saved, and cost per quality-adjusted life-year saved.

RESULTS

Routine MCV-4 vaccination of US adolescents (11 years of age) would prevent 270 meningococcal cases and 36 deaths in the vaccinated cohort over 22 years, a decrease of 46% in the expected burden of disease. Before program costs are counted, adolescent vaccination would reduce direct disease costs by $18 million and decrease productivity losses by $50 million. At a cost per vaccination (average public-private price per dose plus administration fees) of $82.50, adolescent vaccination would cost society $633000 per meningococcal case prevented and $121000 per life-year saved. Key variables influencing results were disease incidence, case-fatality ratio, and cost per vaccination. The cost-effectiveness of toddler vaccination is essentially equivalent to adolescent vaccination, whereas infant vaccination would be much less cost-effective.

CONCLUSIONS

Routine MCV-4 vaccination of US children would reduce the burden of disease in vaccinated cohorts but at a relatively high net societal cost. The projected cost-effectiveness of adolescent vaccination approaches that of recently adopted childhood vaccines under conditions of above-average meningococcal disease incidence or at a lower cost per vaccination.

Antibodies against Haemophilus influenzae type b capsular polysaccharide and tetanus toxoid before and after a booster dose of the carrier protein nine years after primary vaccination with a protein conjugate vaccine

IgG antibodies against Haemophilus influenzae type b (Hib) capsular polysaccharide (CPS) and tetanus toxoid (TT) were measured for 53 children, 10 years of age, before and 1 month after a booster dose of diphtheria-tetanus vaccine (DT). All children had been vaccinated at 3, 5 and 12 months of age with DT and a Hib-TT conjugate. Geometric mean concentrations of Hib CPS serum IgG antibody were 4.16 and 4.30 microg/mL before and after the DT booster, respectively. The geometric mean concentration of TT IgG antibody increased from 0.09 IU/mL to 4.58 IU/mL (P < 0.001). Hib CPS IgG levels remained well above protective titers for 9 years after 3 doses of Hib-TT appropriately spaced in infancy. A booster dose of TT did not affect Hib CPS antibody concentrations but induced a pronounced IgG response against TT.

Invasive Haemophilus influenzae type b infections in vaccinated and unvaccinated children in Canada, 2001-2003

BACKGROUND

Although vaccination of infants against Haemophilus influenzae type b (Hib) invasive infections is effective and has been routinely available in Canada since 1992, cases of the disease continue to occur. We were interested in determining whether recent cases of Hib infection reflected progressive loss of protection with time since vaccination, increasing nonacceptance of vaccination or a deleterious effect of coadministration of recently introduced vaccines such as those for pneumococcal and meningococcal conjugates and hepatitis B. We report on the causes of Hib infections among vaccinated and unvaccinated children between 2001 and 2003 in Canada.

METHODS

Through our established network of 12 pediatric tertiary care hospitals we actively searched for cases in each centre by reviewing daily admissions and laboratory reports, visiting the wards and checking discharge diagnosis codes. Culture-confirmed cases were summarized by nurse monitors using a standardized reporting system.

RESULTS

We identified 29 cases during the 3 years: 16 in 2001, 10 in 2002 and 3 in 2003. Half of the 29 patients had meningitis. Hib infection was more common among children less than 6 months of age (11 cases) and in boys (20 cases). Two deaths occurred (7% case-fatality ratio). A total of 20 children had received no or incomplete primary vaccination because of parental refusal (7 cases), because they were too young to have completed the primary series (11 cases, including 1 in which parental refusal was also a factor) or because of delays in completing the primary series (2 cases); the vaccination history was uncertain in the remaining case. Infection despite primary vaccination occurred in 9 children: 2 previously healthy children and 7 who were immunocompromised or who had a predisposing condition. None of the cases identified in 2003 involved children who had received any of the newly introduced vaccines.

INTERPRETATION

Invasive Hib infections remain rare in Canada, with most cases occurring in children too young to have completed the primary series. Protection after vaccination appears to extend into later childhood and does not appear to be diminished by coadministration of newer infant vaccines.

Haemophilus influenzae type b conjugate vaccines

Haemophilus influenzae type b (Hib) is one of the leading causes of invasive bacterial infection in young children worldwide. During childhood, acquisition of antibody directed against the polysaccharide capsule of the organism, presumably as a result of asymptomatic carriage, confers protection and disease is much less common after the age of 4 years. Like other polysaccharides, the polyribosyl ribitol phosphate (PRP) of the Hib capsule is a T-independent antigen and not immunogenic when administered as a vaccine in infancy. Because the highest rates of disease occur in the first 2 years of life, efficacious Hib vaccines have been designed by covalently linking the PRP capsule to a carrier protein that recruits T-cell help for the polysaccharide immune response and induces anti-PRP antibody production even in the first 6 months of life. Introduction of Hib protein-polysaccharide conjugate vaccines into many industrialized countries over the past 15 years has resulted in the virtual elimination of invasive Hib disease. However, despite the success of the vaccine programme several factors may interfere with the effectiveness of the vaccine in the routine programme, as observed in the UK recently. Such factors may include interference with other concomitant vaccines, waning immunity in the absence of booster doses of vaccine, and reduced natural boosting as a result of decreased transmission of the organism. However, the burden of disease remains highest in resource-poor countries and urgent efforts are needed to provide the benefits of this vaccine for children living in regions where it cannot be used for economic and logistical reasons.