Duration of antibody response after meningococcal polysaccharide vaccination in US Air Force personnel

Safety of Multiple Vaccinations and Durability of Vaccine-Induced Antibodies in an Italian Military Cohort 5 Years after Immunization

We previously examined the safety and immunogenicity of multiple vaccines administered to a military cohort, divided into two groups, the first composed of students at military schools, thus operating inside the national borders for at least 3 years, and the other formed of soldiers periodically engaged in a 9-month-long mission abroad (Lebanon). In the current study, we analyzed 112 individuals of this cohort, 50 pertaining to the first group and 62 to the second group, in order to examine the possible late appearance of side effects and to calculate the half-life of the induced antibodies. Moreover, the possible involvement of B-cell polyclonal activation as a pathogenetic mechanism for long term antibody persistence has even been explored. No late side effects, as far as autoimmunity and/or lymphoproliferation appearance, have been noticed. The long duration of the vaccine induced anti-HAV antibodies has been confirmed, whereas the antibodies induced by tetravalent meningococcal polysaccharide vaccine have been found to persist above the threshold for putative protection for a longer time, and anti-tetanus, diphtheria, and polio 1 and 3 for a shorter time than previously estimated. No signs of polyclonal B-cell activation have been found, as a possible mechanism to understand the long antibody persistence.

Long-term persistence of protective antibodies in Dutch adolescents following a meningococcal serogroup C tetanus booster vaccination

INTRODUCTION

Due to waning immunity, infant vaccination with meningococcal serogroup C conjugated (MenCC) vaccines is insufficient to maintain long-term individual protection. Adolescent booster vaccination is thought to offer direct protection against invasive meningococcal disease (IMD) but also to reduce meningococcal carriage and transmission and in this way establish herd protection in the population. Previously, we studied antibody levels after adolescent MenCC booster vaccination. In the present study, the adolescent vaccinees were revisited after three years to determine antibody persistence and to predict long-term protection.

METHODS

Meningococcal serogroup C tetanus toxoid conjugated (MenC-TT) vaccine was administered to 10-, 12- and 15-year old participants who had been primed nine years earlier with a single dose of MenC-TT vaccine. Blood samples were collected before, 1month, 1year and 3years after the adolescent booster vaccination. Functional antibody levels were measured with serum bactericidal assay using rabbit complement (rSBA). Meningococcal serogroup C polysaccharide and tetanus toxoid specific antibody levels were measured using fluorescent-bead-based multiplex immunoassay. Long-term protection was estimated using longitudinal multilevel antibody decay modeling.

RESULTS

Of the original 268 participants, 201 (75%) were revisited after 3years. All participants still had an rSBA titer above the protective threshold of ⩾8 and 98% ⩾128. The 15-year-olds showed the highest antibody titers. Using a bi-exponential decay model, the median time to fall below the protection threshold (rSBA titer <8) was 16.3years, 45.9years and around 270years following the booster for the 10-, 12- and 15-year-olds, respectively.

CONCLUSIONS

After a first steep decline in antibody levels in the first year after the booster, antibody levels slowly declined between one and three years post-booster. A routine MenC-TT booster vaccination for adolescents in the Netherlands will likely provide long-term individual protection and potentially reduce the risk of resurgence of MenC disease in the general population.

Persistence of serogroup C antibody responses following quadrivalent meningococcal conjugate vaccination in United States military personnel

Serogroup C meningococcal (MenC) disease accounts for one-third of all meningococcal cases and causes meningococcal outbreaks in the U.S. Quadrivalent meningococcal vaccine conjugated to diphtheria toxoid (MenACYW_D) was recommended in 2005 for adolescents and high risk groups such as military recruits. We evaluated anti-MenC antibody persistence in U.S. military personnel vaccinated with either MenACYW_D or meningococcal polysaccharide vaccine (MPSV4). Twelve hundred subjects vaccinated with MenACYW_D from 2006 to 2008 or MPSV4 from 2002 to 2004 were randomly selected from the Defense Medical Surveillance System. Baseline serologic responses to MenC were assessed in all subjects; 100 subjects per vaccine group were tested during one of the following six post-vaccination time-points: 5–7, 11–13, 17–19, 23–25, 29–31, or 35–37 months. Anti-MenC geometric mean titers (GMT) were measured by rabbit complement serum bactericidal assay (rSBA) and geometric mean concentrations (GMC) by enzyme-linked immunosorbent assay (ELISA). Continuous variables were compared using the Wilcoxon rank sum test and the proportion of subjects with an rSBA titer ≥8 by chi-square. Pre-vaccination rSBA GMT was <8 for the MenACWY_D group. rSBA GMT increased to 703 at 5–7 months post-vaccination and decreased by 94% to 43 at 3 years post-vaccination. GMT was significantly lower in the MenACWY_D group at 5–7 months post-vaccination compared to the MPSV4 group. The percentage of MenACWY_D recipients achieving an rSBA titer of ≥8 decreased from 87% at 5–7 months to 54% at 3 years. There were no significant differences between vaccine groups in the proportion of subjects with a titer of ≥8 at any time-point. GMC for the MenACWY_D group was 0.14 µg/mL at baseline, 1.07 µg/mL at 5–7 months, and 0.66 µg/mL at 3 years, and significantly lower than the MPSV4 group at all time-points. Anti-MenC responses wane following vaccination with MenACYW_D; a booster dose is needed to maintain protective levels of circulating antibody.

Vaccination considerations in the asplenic patient

Overwhelming postsplenectomy sepsis is a rare but devastating and often lethal disease. Although vaccines are available, their proper use may be questioned. Standardization of protocols for the immunization of asplenic patients should be universal, thus, likely improving on their use. This article reviews the vaccines to be administered to the asplenic patient.

Persistence of antibodies in laboratory staff immunized with quadrivalent meningococcal polysaccharide vaccine

BACKGROUND

Occupational exposure to live meningococci can potentially cause invasive meningococcal disease in laboratory staff. While, until recently, immunization with quadrivalent polysaccharide vaccine represented one cornerstone of protection, data on long-term persistence of antibodies in adults remain scarce.

METHODS

We analyzed the relationship of antibody levels and time following quadrivalent polysaccharide vaccination (Mencevax® ACWY, GlaxoSmithKline) in a cross-sectional sample of 20 laboratory workers vaccinated at ages between 16.4 to 40.7 years from Germany. Sera were obtained 0.4 to 158.5 (median 35.3) months after vaccination. At the time of sampling, laboratory workers had been regularly exposed to meningococci for periods between 3.2 to 163.8 (median 41.2) months. Serum bactericidal assay (SBA) with rabbit complement and a microsphere-based flow analysis method were used to determine bactericidal titers and concentrations of IgG, respectively, against serogroups A, C, W135, and Y. Decay of antibodies was modeled using linear regression. Protective levels were defined as SBA titers ≥ 8.

RESULTS

Half-lives of SBA titers against serogroups A, C, W135, and Y were estimated at 27.4, 21.9, 18.8, and 28.0 months, respectively. Average durations of protection were estimated at 183.9, 182.0, 114.6, and 216.4 months, respectively. Inter-individual variation was high; using lower margins of 95% prediction intervals, minimal durations of protection against serogroups A, C, W135 and Y were estimated at 33.5, 24.6, 0.0, and 55.1 months, respectively. The proportion of staff with protective SBA titers against W135 (65.0%) was significantly lower than proportions protected against A (95.0%), C (94.7%), and Y (95.0%). Consistently, geometric mean titer (97.0) and geometric mean concentration of IgG (2.1 μg/ml) was lowest against serogroup W135. SBA titers in a subset of individuals with incomplete protection rose to ≥ 128 (≥ 8 fold) after reimmunization with a quadrivalent glycoconjugate vaccine.

CONCLUSIONS

The average duration of protection following immunization with a quadrivalent polysaccharide vaccine in adults was ≥ 115 months regardless of serogroup. A substantial proportion (approximately 23% according to our decay model) of adult vaccinees may not retain protection against serogroup W135 for five years, the time suggested for reimmunization.

Use and interpretation of diagnostic vaccination in primary immunodeficiency: a working group report of the Basic and Clinical Immunology Interest Section of the American Academy of Allergy, Asthma & Immunology

A major diagnostic intervention in the consideration of many patients suspected to have primary immunodeficiency diseases (PIDDs) is the application and interpretation of vaccination. Specifically, the antibody response to antigenic challenge with vaccines can provide substantive insight into the status of human immune function. There are numerous vaccines that are commonly used in healthy individuals, as well as others that are available for specialized applications. Both can potentially be used to facilitate consideration of PIDD. However, the application of vaccines and interpretation of antibody responses in this context are complex. These rely on consideration of numerous existing specific studies, interpolation of data from healthy populations, current diagnostic guidelines, and expert subspecialist practice. This document represents an attempt of a working group of the American Academy of Allergy, Asthma & Immunology to provide further guidance and synthesis in this use of vaccination for diagnostic purposes in consideration of PIDD, as well as to identify key areas for further research.

Importance of circulating antibodies in protection against meningococcal disease

Neisseria meningitidis infection results in life-threatening illnesses, including bacteremia, sepsis and meningitis. Early diagnosis and treatment are a challenge due to rapid disease progression, resulting in high mortality and morbidity in survivors. Disease can occur in healthy individuals, however, risk of infection is higher in patients with certain risk factors. N meningitidis carriage and case-fatality rates are high in adolescents and young adults. The absolute incidence of meningococcal disease has decreased partially due to increasing meningococcal vaccination rates. Maintaining protective levels of circulating antibodies by vaccination is necessary for clinical protection against disease. The Centers for Disease Control and Prevention Advisory Committee on Immunization Practices guidelines recommend vaccination for all individuals aged 11 through 12 years, followed by a booster dose at age 16 years for maintenance of protective antibody levels throughout the high-risk years. Despite these guidelines, many adolescents remain unvaccinated and susceptible to infection and disease. 

Serum antibody kinetics following nasal or parenteral challenge with meningococcal polysaccharide in healthy adults

Limited data are available on the kinetics of meningococcal serogroup C (MenC)-specific antibody responses following parenteral or nasal challenge in those who have received prior MenC vaccination (polysaccharide or conjugate). Young adults who had previously received either meningococcal A/C polysaccharide (MACP) or MenC conjugate (MCC) vaccine or naïve subjects were challenged with MACP via one of two routes, nasal or parenteral. Blood samples were taken prevaccination and on days 1 to 4 and day 10 postvaccination. MenC serum bactericidal antibody (SBA) and MenC-specific IgG were measured. Following parenteral challenge, MenC SBA and IgG responses were seen to occur between 4 and 7 days postchallenge. A lower proportion of subjects responded following nasal challenge, with naïve subjects showing little change in SBA geometric mean titer (GMT) and IgG geometric mean concentration (GMC) over the 10 days following challenge. Increases in SBA GMTs were seen between 4 and 7 days after nasal challenge in those who had received prior MCC and between 7 and 10 days in those who had received prior MACP, and the responses in the prior-MACP group were of lower magnitude than the responses of the prior-MCC group. The data presented here indicate that, following MCC vaccination, memory has been induced at the mucosal level, and these subjects were able to respond with increases in SBA levels. These results demonstrate that the speed of response (primary or secondary) to challenge with MenC polysaccharide via the nasal or parenteral route does not differ and support concerns that immunological memory alone is too slow to provide protection.

Serum antibody responses in Ethiopian meningitis patients infected with Neisseria meningitidis serogroup A sequence type 7

To elucidate critical components of protective immune responses induced during the natural course of serogroup A meningococcal disease, we studied acute-, early-convalescent-, and late-convalescent-phase sera from Ethiopian patients during outbreaks in 2002 to 2003. Sera were obtained from laboratory-confirmed patients positive for serogroup A sequence type 7 (ST-7) meningococci (A:4/21:P1.20,9) (n = 71) and from Ethiopian controls (n = 113). The sera were analyzed using an enzyme-linked immunosorbent assay to measure levels of immunoglobulin G (IgG) against serogroup A polysaccharide (APS) and outer membrane vesicles (OMVs) and for serum bactericidal activity (SBA) using both rabbit and human complement sources. Despite relatively high SBA titers and high levels of IgG against APS and OMVs in acute-phase patient sera, significant increases were seen in the early convalescent phase. Antibody concentrations returned to acute-phase levels in the late convalescent phase. Considering all patients' sera, a significant but low correlation (r = 0.46) was observed between SBA with rabbit complement (rSBA) using an ST-5 reference strain and SBA with human complement (hSBA) using an ST-7 strain from Ethiopia. While rSBA demonstrated a significant linear relation with IgG against APS, hSBA demonstrated significant linear relationships with IgG against both APS and OMV. This study indicates that antibodies against both outer membrane proteins and APS may be important in providing the protection induced during disease, as measured by hSBA. Therefore, outer membrane proteins could also have a role as components of future meningococcal vaccines for the African meningitis belt.

Prevention of meningococcal disease

Neisseria meningitidis is the most common cause of meningitis in children aged 2-18 with a mortality rate ranging from 4-40% and substantial morbidity in 11-19% of survivors. Of the four serogroups ofNeisseria meningitidis, serogroups B and C are the most common causes in the United States, with serogroup C causing most disease among adolescents, a population at risk for invasive meningococcal disease. The meningococcal polysaccharide vaccine was developed in response to increasing rates of bacterial meningitis among military recruits. With widespread use of the vaccine in the military, there was a dramatic decreased incidence in invasive meningococcal disease. However, there may be limitations to the polysaccharide vaccine including lack of durable protection, lack of induction of T-cell-dependent immune response, and lack of immunogenicity in children less than 2 years of age. Based on the success of other conjugate vaccines in pediatrics, a new conjugate polysaccharide vaccine, Menactra, has been approved by the Food and Drug Administration and recommended for routine vaccination in adolescents by the Advisory Committee on Immunization Practices.

Prospects for vaccine prevention of meningococcal infection

Neisseria meningitidis is the leading cause of bacterial meningitis in the United States and worldwide. A serogroup A/C/W-135/Y polysaccharide meningococcal vaccine has been licensed in the United States since 1981 but has not been used universally outside of the military. On 14 January 2005, a polysaccharide conjugate vaccine that covers meningococcal serogroups A, C, W-135, and Y was licensed in the United States for 11- to 55-year-olds and is now recommended for the routine immunization of adolescents and other high-risk groups. This review covers the changing epidemiology of meningococcal disease in the United States, issues related to vaccine prevention, and recommendations on the use of the new vaccine.

Polysaccharide vaccines for preventing serogroup A meningococcal meningitis

BACKGROUND

Randomised trials carried out over two decades ago showed that the polysaccharide vaccine prevented serogroup A meningococcal meningitis. Subsequent non-randomised studies, however, suggested significant variations in the age-specific duration of protection among young children.

OBJECTIVES

The aim of the review was to determine the effect of polysaccharide serogroup A vaccine for preventing serogroup A meningococcal meningitis. The specific objectives were to assess the age-specific effects of the vaccine, the effect of booster doses in children under five years of age, and the duration of protection in children and adults.

SEARCH STRATEGY

In 2004, the review was updated. The following databases were searched for records of new trials: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 4, 2004); MEDLINE (January 1966 to November Week 1 2004); and EMBASE (January 1990 to September 2004).

SELECTION CRITERIA

The first stage of the review included randomised trials. The second stage included non- randomised studies that addressed specific outcomes not answered by the randomised trials.

DATA COLLECTION AND ANALYSIS

One reviewer assessed the methodological quality of the randomised trials and two reviewers independently identified and assessed the non-randomised studies. Of the twelve eligible Randomized trials, four were excluded because of the high risk of bias in assessing vaccine efficacy. Data from the trials were pooled using the Exact method to assess vaccine efficacy at one, two and three years post vaccination. Of the 15 non-randomised studies, only two addressed the specific objectives not answered by the randomised trials but were assessed to be at high risk of bias.

MAIN RESULTS

The protective effect within the first year of vaccination was consistent across the randomised trials, and the summary vaccine efficacy was 95% (95% confidence interval (CI) 87% to 99%). Protection extended into the second and third year after vaccination but the results did not attain statistical significance. The vaccine was protective in Finnish children aged 3 months to five years. The latter was also the only trial that assessed the effect of a booster dose in children under two years of age but lacked power to yield statistically significant results. The vaccine was protective in one- to five-year old children in developing countries (Nigeria and Sudan) but the age-specific efficacy in strata between one and five years of age could not be determined.

AUTHORS' CONCLUSIONS

For the first year after vaccination, the polysaccharide serogroup A vaccine was strongly protective against serogroup A meningococcal meningitis in participants over five years of age. It was also protective beyond the first year after vaccination in this age group but the level of vaccine efficacy could not be determined with precision. Children aged one to five years in developing countries were also protected but the level of efficacy in this age group could not be determined. While the vaccine was strongly protective among children aged three months to five years in developed countries the level of efficacy across age strata within this age group could not be determined. The number of children aged under two years was too small to draw conclusions on the protective effect of a booster dose of vaccine.

Review of the cost effectiveness of immunisation strategies for the control of epidemic meningococcal meningitis

Outbreaks of meningococcal disease have caused devastation worldwide. Effective vaccines have not been used routinely, due to perceived limitations of the duration of effectiveness as well as immunogenicity when administered during infancy. Given the sporadic nature of outbreaks, the optimal use of these vaccines to control both short-term epidemic and endemic meningococcal disease has been the subject of much debate. Seven economic studies on the use of polysaccharide vaccination strategies help to highlight the relevant epidemiological and economic issues surrounding the decisions for their use. Five of these studies were based in Africa, the region where annual incidence rates can be several orders of magnitude greater than the rest of the world. These studies demonstrated that vaccination against meningococcal disease during outbreak situations is suboptimal given the inability to rapidly immunise populations in a timely fashion in resource-poor areas. However, depending on the disease incidence and the ability to deliver vaccines, the polysaccharide vaccine can be cost effective for preventive strategies when given prior to the start of outbreaks, either through presumptive vaccination or through a modified routine delivery strategy. Economic analyses of mass immunisation campaigns and modelled routine vaccination suggest that routine use of meningococcal vaccines for preventive strategies could be within the range of cost-effective public health interventions in those regions of the world where meningococcal disease is endemic. This includes the meningococcal belt of Africa, the Sahelian region.

Meningococcal conjugate vaccines

Neisseria meningitidis is a leading cause of bacterial meningitis and sepsis in the US, Europe and in many other parts of the world, including parts of sub-Saharan Africa (known as the African 'meningitis belt'). There are > 500000 cases of meningococcal disease annually with an estimated death toll of 135000 worldwide. Approximately 10 - 15 % of survivors experience significant morbidity in the form of neurological sequelae, including hearing loss, speech disorders, loss of limbs, mental retardation and paralysis. Disease is usually caused by N. meningitidis serogroups A, B, C, Y or W-135. Prevention of meningococcal disease includes isolation, chemoprophylaxis and vaccination with available polysaccharide vaccines. However, the polysaccharide meningococcal vaccines (i.e., A and C; A, C and W-135; or A, C, Y and W-135) initially developed in the 1970s are generally poorly immunogenic in children or require repeated doses and do not produce long-lasting immunity. Conjugate vaccine technology has been very successfully used in childhood vaccines for the prevention of other bacterial meningitis pathogens, including vaccines against Haemophilus influenzae serotype b (Hib) and more recently, the seven- and nine-valent conjugate pneumococcal vaccines. Newly released meningococcal conjugate vaccines against N. meningitidis serogroup C have been highly efficacious in young children and adolescents, with minimal side effects. Conjugate vaccines targeting other important meningococcal serogroups (e.g., N. meningitidis serogroup A, responsible for the large pandemic outbreaks and the majority of disease in sub-Saharan Africa and serogroups Y and W-135) are under development and together with the serogroup C conjugates, have the potential to significantly impact worldwide sporadic and epidemic meningococcal disease. The search for an effective serogroup B meningococcal vaccine remains elusive. This manuscript reviews the conjugate meningococcal vaccines and their potential for meningococcal disease prevention.

Opportunities for Control of Meningococcal Disease in the United States

The United States currently has relatively low rates of meningococcal disease caused by Neisseria meningitidis. Serogroups Y, C, and B are most common. Although most cases are sporadic, a minority are associated with outbreaks. Pediatric populations have disproportionately higher rates of disease, but nearly two thirds of all cases occur in persons aged 15 years and older. The major challenge to control of domestic meningococcal disease is the absence of a vaccine to prevent sporadic cases spanning many age groups. The quadrivalent A/C/Y/W-135 meningococcal polysaccharide vaccine is licensed in the United States, but because of its limited efficacy in children under two years of age, it is recommended for high-risk groups and outbreak response rather than routine childhood immunization. New conjugate meningococcal vaccines have successfully reduced endemic disease in the United Kingdom, and similar vaccines promise to have a dramatic impact on the burden of meningococcal disease in the United States.

Should university students be vaccinated against meningococcal disease in Canada?

OBJECTIVE

To evaluate the benefit and costs of vaccination of university students against invasive meningococcal disease (IMD) in Canada.

METHODS

Published studies were reviewed and a simulation model was used.

RESULTS

IMD risk seems to be of low magnitude, but consequences can be dramatic. Over a 10-year period, IMD risk reduction would be slightly greater using a monovalent C conjugate vaccine than a quadrivalent polysaccharide vaccine. From a societal perspective, costs per quality-adjusted life-years gained would be between $135,000 and $698,000, according to epidemiological scenarios and with vaccine purchase prices between $35 and $50 per dose.

CONCLUSIONS

Economic indices exceed proposed criteria for cost effective public health programs, but from the perspective of students and parents, the cost of vaccination might be worth the benefit.

Critical analysis of old and new vaccines against N. meningitidis serogroup C, considering the meningococcal disease epidemiology in Brazil

Worldwide, the impact of meningococcal disease is substantial, and the potential for the introduction and spread of more virulent strains of N. meningitidis or strains with increased resistance to current antibiotics causes concern, making prevention essential.

OBJECTIVES

Review the indications for meningococcal disease vaccines, considering the epidemiological status in Brazil.

METHODS

A critical literature review on this issue using the Medline and Lilacs databases.

RESULTS

In Brazil, MenB and MenC were the most important serogroups identified in the 1990s. Polysaccharide vaccines available against those serogroups can offer only limited protection for infants, the group at highest risk for meningococcal disease. Additionally, polysaccharide vaccines may induce a hypo-responsive state to MenC. New meningococcal C conjugate vaccines could partially solve these problems, but it is unlikely that in the next few years a vaccine against MenB that can promote good protection against multiple strains of MenB responsible for endemic and epidemic diseases will become available.

CONCLUSIONS

In order to make the best decision about recommendations on immunization practices, better quality surveillance data are required. In Brazil, MenC was responsible for about 2,000 cases per year during the last 10 years. New conjugate vaccines against MenC are very effective and immunogenic, and they should be recommended, especially for children less than 5 years old. Polysaccharide vaccines should be indicated only in epidemic situations and for high-risk groups. Until new vaccines against MenC and MenB are available for routine immunization programs, the most important measure for controlling meningococcal disease is early diagnosis of these infections in order to treat patients and to offer chemoprophylaxis to contacts.

Disparity in functional activity between serum anticapsular antibodies induced in adults by immunization with an investigational group A and C Neisseria meningitidis-diphtheria toxoid conjugate vaccine and by a polysaccharide vaccine

Polysaccharide-protein conjugate vaccines elicit higher concentrations of serum anticapsular antibody in infants and children than do unconjugated polysaccharide vaccines. The conjugate-induced antibodies also have higher avidity and complement-mediated bactericidal activity. Similar vaccine-related differences in the magnitude or functional activity of antibody are observed infrequently in immunized adults. We compared the antibody responses of adults immunized with an investigational group A and C meningococcal conjugate vaccine to those elicited by an unconjugated meningococcal polysaccharide vaccine. Although there were no significant differences between the respective geometric mean bactericidal titers of the two vaccine groups, it took, on average, three- to fourfold higher concentrations of polysaccharide-induced serum anticapsular antibody to achieve 50% complement-mediated bacteriolysis than conjugate-induced antibody (P < 0.001 for groups A and C). At limiting doses, the polysaccharide-induced anticapsular antibodies also were less effective in conferring passive protection against meningococcal bacteremia in infant rats challenged with a group C strain (P < 0.04). The avidity index of the group C antibodies was higher in the conjugate vaccine group than in the polysaccharide vaccine group (P < 0.005). The disparities in the functional activity of the anticapsular antibodies elicited in adults by the two vaccines imply fundamental differences in the respective B-cell populations stimulated.

Meningococcal vaccines: a progress report

Neisseria meningitidis causes a wide range of human disease and remains a common cause of septicaemia and meningitis. Meningococcal serogroups A, B, C and Y cause the majority of cases of invasive disease in the US and throughout the world, with epidemics usually caused by serogroups A and C. Most patients with meningococcaemia, with or without meningitis, respond to standard antimicrobial therapy with either penicillin or ampicillin, but the recent emergence of meningococcal strains that are intermediately resistant to penicillin may alter these recommendations in the future. Given the devastating nature of meningococcal disease and emergence of these resistant strains, prevention (specifically through vaccination) remains the best approach to control this serious infection. A polysaccharide meningococcal vaccine is efficacious against disease caused by serogroups A, C, Y and W135, but is not effective in infants and children aged <2 years, and the duration of efficacy decreases markedly during the first 3 years after a single dose of the vaccine. Conjugate meningococcal vaccines have been developed to address these concerns. Initial studies with the meningococcal C conjugate vaccine have shown that the vaccine is safe and immunogenic and provides a T cell-dependent antigen that can be boosted by further doses of vaccine, or following exposure to the homologous organism or cross-reacting antigens. The UK recently implemented routine vaccination with the meningococcal C conjugate vaccine to all infants, and to all persons aged >1 year in a catch-up programme to immunise all school-aged children and young adults up to 20 years of age. Early postlicensure data indicate that this vaccine has shown significant efficacy in reduction of invasive meningococcal disease in these age groups. The full impact of vaccination will be determined once all age groups are immunised.

Vaccinating first-year college students living in dormitories for Meningococcal disease: an economic analysis

BACKGROUND

Surveillance of meningococcal disease among U.S. college students found an elevated rate of this disease among first-year students living in dormitories.

OBJECTIVE

This study examines the economics of routinely vaccinating a cohort of 591,587 incoming first-year students who will live in dormitories for > or =1 years.

METHODS

A cost-benefit model (societal perspective) was constructed to measure the net present value (NPV) of various vaccination scenarios, as well as the cost/case and cost/death averted. Input values included hospitalization costs from $10,924 to $24,030 per hospitalization; immunization costs (vaccine plus administration costs) from $54 to $88 per vaccine; 30 nonfatal, vaccine-preventable cases over a 4-year period (includes 3 with sequelae); 3 premature deaths; value of human life from $1.2 million to $4.8 million; and long-run sequelae costs from $1298 to $14,600. Sensitivity analyses were also conducted on vaccine efficacy (80% to 90%); discount rate (0% to 5%); and coverage (60% to 100%).

RESULTS

The costs of vaccination outweighed the benefits gained with NPVs ranging from -$11 million to -$49 million. The net cost per case averted ranged from $0.6 million to $1.9 million. The net cost per death averted ranged from $7 million to $20 million. The break-even costs of vaccination (when NPV=$0) at 60% coverage ranged from $23 (90% vaccine efficacy) to $5 (80% efficacy).

CONCLUSIONS

The model showed that the vaccination program is not cost-saving. Key variables influencing the results were the low number of vaccine-preventable cases and the high cost of vaccination. However, from the perspective of students and parents, the cost of vaccination might be worth the real or perceived benefit of reducing the risk to an individual student of developing meningococcal disease.

Effect of O acetylation of Neisseria meningitidis serogroup A capsular polysaccharide on development of functional immune responses

The importance of O-acetyl groups to the immunogenicity of Neisseria meningitidis serogroup A polysaccharide (PS) was examined in studies using human sera and mouse immunization. In 17 of 18 postimmunization human sera, inhibition enzyme-linked immunosorbent assay indicated that the majority of antibodies binding to serogroup A PS were specific for epitopes involving O-acetyl groups. Studies with mice also showed an essential role for O-acetyl groups, where serum bactericidal titers following immunization with de-O-acetylated (de-O-Ac) conjugate vaccine were at least 32-fold lower than those following immunization with O-Ac PS-conjugate vaccine and 4-fold lower than those following immunization with native capsular PS. Inhibition studies using native and de-O-Ac PS confirmed the specificity of murine antibodies to native PS. The dramatic reduction in immunogenicity associated with removal of O-acetyl groups indicates that O acetylation is essential to the immunogenic epitopes of serogroup A PS. Since levels of bactericidal antibodies are correlated with protection against disease, O-acetyl groups appear to be important in protection.

Standardization of Neisseria meningitidis serogroup B colorimetric serum bactericidal assay

The correlate of protection for serogroup B meningococci is not currently known, but for serogroup C it is believed to be the serum bactericidal assay (SBA). The current SBAs are labor intensive and the variations in protocols among different laboratories make interpretation of results difficult. A colorimetric SBA (cSBA), based on the ability of Neisseria meningitidis serogroup B to consume glucose, leading to acid production, was standardized by using group B strain Cu385-83 as the target. The cSBA results were compared to those obtained for a traditional colony-counting microassay (mSBA). Glucose and bromocresol purple pH indicator were added to the medium in order to estimate growth of cSBA target cell survivors through color change. Different variants of the assay parameters were optimized: growth of target cells (Mueller Hinton agar plates), target cell number (100 CFU/per well), and human complement source used at a final concentration of 25%. After the optimization, three other group B strains (H44/76, 490/91, and 511/91) were used as targets for the cSBA. The selection of the assay parameters and the standardization of cSBA were done with 13 sera from vaccinated volunteers. The titers were determined as the higher serum dilution that totally inhibited the bacterial growth marked by the color invariability of the pH indicator. This was detected visually as well as spectrophotometrically and was closely related to a significant difference in the growth of target cell survivors determined using Student's t test. Intralaboratory reproducibility was +/-1 dilution. The correlation between bactericidal median titers and specific immunoglobulin G serum concentration by enzyme immunoassay was high (r = 0.910, P < 0.01). The bactericidal titers generated by the cSBA and the mSBA were nearly identical, and there was a high correlation between the two assays (r = 0.974, P < 0.01). The standardized cSBA allows easy, fast, and efficient evaluation of samples.

Immune response induction and new effector mechanisms possibly involved in protection conferred by the Cuban anti-meningococcal BC vaccine

This report explores the participation of some afferent mechanisms in the immune response induced by the Cuban anti-meningococcal vaccine VA-MENGOC-BC. The induction of delayed-type hypersensitivity in nursing babies and lymphocyte proliferation after immunization is demonstrated. The presence of gamma interferon IFN-gamma and interleukin-2 (IL-2) mRNAs but absence of IL-4, IL-5, and IL-10 mRNAs were observed in peripheral blood mononuclear cells from immunized subjects after in vitro challenge with outer membrane vesicles. In addition, some effector functions were also explored. The presence of opsonic activity was demonstrated in sera from vaccinees. The role of neutrophils as essential effector cells was shown. In conclusion, we have shown that, at least in the Cuban adult population, VA-MENGOC-BC induces mechanisms with a T-helper 1 pattern in the afferent and effector branches of the immune response.

Comparison of cost-effectiveness of preventive and reactive mass immunization campaigns against meningococcal meningitis in West Africa: a theoretical modeling analysis

For epidemic meningitis control in sub-Saharan Africa, the World Health Organization recommends a strategy of emergency vaccination with meningococcal A + C polysaccharide vaccine when epidemic thresholds are exceeded. An alternative strategy for areas without effective surveillance systems is mass preventive campaigns before outbreaks occur. A model was formulated to simulate epidemics and to compare the cost-effectiveness of these two strategies for the district of Matam, Senegal, where an actual preventive campaign was performed during 1997. The preventive strategy prevented 59% of the cases compared to 49% for the emergency strategy. The cost per case prevented was US$59 for the preventive strategy and US$133 for the reactive strategy, and the preventive strategy saved US$0.20 per habitant. Preventive meningococcal vaccination through mass campaigns prevented more outcomes at a lower cost, provided that the occurrence of an epidemic could be predicted within 3 years and that the vaccination coverage rates for the preventive and standard strategies were > 70% and < 94%, respectively. Sub-Saharan African countries without effective surveillance systems should consider mass preventive campaigns while awaiting an affordable conjugate vaccine.

Meningococcal vaccines

Global control and prevention of meningococcal disease depends on the further development of vaccines that overcome the limitations of the current polysaccharide vaccines. Protein-polysaccharide conjugate vaccines likely will address the marginal protective antibody responses and short duration of immunity in young children derived from the A, C, Y, and W-135 capsular polysaccharides, but they will be expensive to produce and purchase, and may not offer a practical solution to the countries with greatest need. In addition, OMP vaccines have been tested extensively in humans and hold some promise in the development of a serogroup B vaccine, but are limited by the antigenic variability of these subcapsular antigens and the resulting strain-specific protection. Elimination of meningococcal disease likely will require a novel approach to vaccine development, ideally incorporating a safe and effective antigen or antigens common to all meningoccocal serogroups. As a solely human pathogen, however, N. meningitidis has developed many tools with which to evade the human immune system, and likely will pose a formidable challenge for years to come.

Immunologic correlates of protection induced by vaccination

Vaccine design and licensing depend on the choice of protective antigens and the demonstration of their efficacy. Ideally efficacy correlates with some measurement of immune response, although occasionally the correlation is weak and in the case of some vaccines uncertain. This paper attempts to review what is known about correlates of vaccine-induced protection. Although mucosal and cellular immune responses are clearly important to protection by some vaccines, most vaccines licensed today depend for their efficacy on serum antibodies. Particular levels of antibodies can be identified that confer protection most of the time. A condition for the efficacy of antibodies is functionality, i.e. their ability to kill or inactivate pathogens. The immune system is redundant, and the different types of responses to vaccines act synergistically.

Tetravalent meningococcal polysaccharide vaccine is immunogenic in adult allogeneic BMT recipients

Forty-four adult BMT recipients transplanted from an HLA-identical sibling donor were randomized to receive meningococcal polysaccharide (Men PS) vaccine either 8 (early group; 22 patients) or 20 (late group; 22 patients) months after BMT. The geometric mean concentrations (GMC) of antibodies to serogroup A Neisseria meningitidis (Men A) and serogroup C Neisseria meningitidis (Men C), determined by an EIA method, decreased during the first 6 months after BMT but remained at a stable level thereafter. Before vaccination the GMCs of anti-Men A were 1.53 microg/ml and 1.61 microg/ml, but 1 month after vaccination they were significantly higher, 3.46 microg/ml and 6.39 microg/ml, in the early and late groups. The GMCs of anti-Men C increased from 0.37 microg/ml and 0.44 microg/ml before vaccination to 3.31 microg/ml and 4.62 microg/ml at 1 month after vaccination in the early and late groups, respectively. By 6 months after vaccination the GMCs of Men antibodies had decreased to levels of about 50% of those measured at 1 month after vaccination. Two-fold responses to Men A PS were seen in 52% and 74% and to Men C PS in 76% and 89% of the BMT recipients in the early and late groups, respectively. Chronic GVHD had no influence on the vaccination response. In the present study, Men PS vaccine induced good and equal antibody responses to Men A and Men C PSs in allogeneic BMT recipients regardless of timing after BMT. Vaccination against Neisseria meningitidis should be considered, especially in the event of travelling or military service > or = 8 months after BMT.

Predictors of vaccination rates during a mass meningococcal vaccination program on a college campus

Factors contributing to students' compliance with mass vaccination programs during meningococcal outbreaks have not been well described. A 1997 mass vaccination campaign at Michigan State University provided an opportunity to study such factors. Of 34,024 students in the target population, 17,538 (51.5%) were vaccinated in 5 days. Vaccination rates were higher for women (47.9%) than for men (43.1%) and higher for on-campus residents (65.3%) than for off-campus residents (35.6%). For each year of students' age beyond 19, the adjusted odds of vaccination were reduced by 0.82. Adjusted odds ratios for vaccination, with White students as the reference group at 1.0, were 1.33 for Asian American students, 0.97 (not significant) for Hispanic students, 0.82 for African American students, and 0.80 for Native American students. Students from the Colleges of Business, Engineering, Communication, and Natural Science had the highest vaccination rates; those from the College of Arts and Letters had the lowest rates.

Update on Haemophilus influenzae serotype b and meningococcal vaccines

Use of conjugate Haemophilus influenzae type b (Hib) vaccines has resulted in the near elimination of Hib invasive disease among infants in the United States in only 10 years, which places this intervention among the most notable public health achievements of the past decade. This has radically altered our perception of the major causes of bacterial meningitis and invasive bacterial disease among children, increasing the prominence of meningococcal disease as an important cause of childhood and adult meningitis and leading researchers to apply the same conjugate technology to the development of improved vaccines for Neisseria meningitidis. Use of conjugated meningococcal vaccines against serogroups A, C, Y, and W-135 are expected to offer the possibility of better control of sporadic disease and outbreaks throughout developed and developing countries within the next 5 years.

Development of antibodies against tetravalent meningococcal polysaccharides in revaccinated complement-deficient patients

Individuals deficient in C3 or a late complement component are susceptible to recurrent meningococcal infections. Since they experience meningococcal episodes mostly with uncommon meningococcal serogroups, vaccination with a tetravalent vaccine containing A, C, Y and W135 polysaccharides has been suggested. We vaccinated a cohort of two C3 and 17 late complement component-deficient (LCCD) patients, revaccinated them 7 years later and investigated the development of their IgG antibodies to the capsular polysaccharides of the meningococcal vaccine. Seven years after the first vaccination levels of IgG antibodies declined compared with the levels present at 6 months after the first vaccination, but were still at least four times higher than before vaccination. Levels of antibodies to Y polysaccharide in serum of complement-deficient patients were rather low but they did not differ significantly from those in serum of healthy non-related controls (P = 0.07). Three months after the second vaccination IgG antibodies against all polysaccharides increased, exceeding those measured at 6 months after the first vaccination. In the 8 years of observation after the first vaccination two new meningococcal infections with strains related to the vaccine (serogroup Y strains) occurred in two patients, 3.5 and 5 years after the first vaccination. Our findings show that high IgG antibody levels against the tetravalent meningococcal polysaccharide vaccine were reached after revaccination of two C3 and 17 LCCD individuals 7 years after the first vaccination. Whether revaccination should be required within a period shorter than 7 years is discussed, since two vaccinees developed meningococcal disease to vaccine serogroup Y.

Polysaccharide vaccines for preventing serogroup A meningococcal meningitis

BACKGROUND

Controlled trials over two decades ago showed that the polysaccharide vaccine prevented meningococcal meningitis. Subsequent observational studies suggested variations in the level and duration of protection, particularly among young children.

OBJECTIVES

To determine the effect of polysaccharide serogroup A vaccine for preventing serogroup A meningococcal meningitis.

SEARCH STRATEGY

MEDLINE and the Cochrane Controlled Trials Register.

SELECTION CRITERIA

Randomised and other prospective controlled trials.

DATA COLLECTION AND ANALYSIS

One reviewer collected data and assessed the methodologic quality of the trials. Data were pooled using the Exact method to assess vaccine efficacy at one, two and three years post-vaccination.

MAIN RESULTS

The protective effect within the first year was consistent across all eight trials, including one with participants exclusively under six years of age (in Finland); overall vaccine efficacy was 95% (Exact 95% CI 87%, 99%). The Finnish trial lacked statistical power to assess the effect of a booster dose given to children less than 18 months old. In the three other trials that included children less than six years old (one in Sudan and two in Nigeria), none of the vaccinated children developed meningitis, but the statistical significance of this finding was undetermined. Protection extended into the second (in two studies) and third (in one study) years after vaccination, but these results were also not statistically significant.

REVIEWER'S CONCLUSIONS

When compared with current recommendations, the methodological quality and relative incompleteness of the published reports could arguably render the trials invalid for this review. However, it was unlikely that the results of the trials in such diverse settings would have been biased towards a strong and consistent protective effect. Immunogenicity trials were not included in this review. Stage two of the review will assess the vaccine effect from observational studies.

Safety and immunogenicity of a new Neisseria meningitidis serogroup C-tetanus toxoid conjugate vaccine in healthy adults

We evaluated the safety and immunogenicity of a single dose of a new serogroup C O-deacetylated meningococcal polysaccharide-tetanus toxoid conjugate vaccine in 30 healthy adult volunteers. The vaccine was well tolerated with no serious adverse events and minimal local reactions and systemic symptoms. All subjects developed a fourfold or greater increase in serum bactericidal antibody (SBA) to serogroup C meningococcus. SBA geometric mean titre increased from 11 to 3649 (p<0.001). Serogroup C-specific IgG levels increased postvaccination from 0.65 to 17.02 microg/ml (p<0.001). Bactericidal titres pre- and postimmunisation showed significant correlation with serogroup C-specific IgG (r(2)=0.693). Antibody levels fell by 6 months postvaccination, however, meningococcal C IgG avidity increased indicating the successful induction of a T-cell-dependent antibody response.

CONCLUSION

meningococcal C-tetanus toxoid conjugate vaccine is immunogenic and well tolerated in healthy adults.

A cost-effectiveness analysis of vaccination strategies against N. meningitidis meningitis in sub-Saharan African countries

This analysis evaluates the cost-effectiveness (C/E) of routine vaccination against Neisseria meningitidis. Three different preventive strategies are analyzed: mass vaccination during epidemics (the current standard of care), routine preventive vaccination and a combination strategy of routine vaccination with mass vaccination during epidemics. A Markov model is used to simulate the epidemics of meningitis in a cohort of 5-year old children and compare these different strategies. The results show that mass vaccination strategy is dominated by the two other strategies. The incremental C/E ratios are US$50/QALY for the routine vaccination, and US$199/QALY for the combination strategy. The costs per fatal case averted are US$1161 for the routine vaccination, and US$2397 for the combination strategy. The C/E ratios are sensitive to: the incidence of meningococcal meningitis, the costs of treating cases, the costs of routine vaccination and the costs and effectiveness of mass immunization campaign. However the rank ordering of the strategies is almost never altered. In conclusion, the results of this analysis suggest that mass vaccination in sub-Saharan Africa in case of epidemics should be reconsidered. Routine vaccination against meningococcal meningitis at an early age, with or without mass vaccination during epidemics is more effective, with a C/E ratio within the range of other vaccination strategies currently in place in Africa.

[Meningococcal C disease epidemic in Galicia 1996: the decision making process]

In this article we describe the decision making process used to choose the best alternative for bringing under control an epidemic of meningococcal C disease, which occurred in Galicia in 1996. In the decision making process, we used a methodology which consisted on the identification and definition of a problem, in order to identify alternative solutions and to select one, and finally implement and evaluate it. The health problem was detected studying the data obtained from a survey conducted following an outbreak of meningococcal C disease in february 1995 and from the active epidemiological surveillance system created thereafter. Because this was a new, complex and severe problem, with far-reaching social consequences, critical for our organization, and with long-term implications, and because it was considered important to take the decision as objectively as possible and to clearly explain it, the methodology chosen to solve the problem was a non-programmed, multicriteria making decision process, carried out by a working group using a criterion weighting approach. This working group was created within the General Directorate of Public Health, composed of specialist and of people responsible for the different areas involved. The working group put into practice the different steps of the methodology. The assessment criteria and their respective weights were: effect (efficacy measured by the number of cases we could have prevented if the alternatives were applied in the previous season) 40%; cost (in millions of pesetas) 15%; acceptability (acceptance of and response to each strategy from different groups: general population, health care professionals, other Administrations with competency in Public Health) 30%; and coherence (adherence to the currently accepted strategies for disease control in other countries)15%. When these criteria were applied to the ten alternatives considered, a score was obtained for each one of them. The highest scoring alternative corresponded to the massive vaccination of the total population of Galicia between 18 months and 19 years of age.

Protection against meningococcal serogroup ACYW disease in complement-deficient individuals vaccinated with the tetravalent meningococcal capsular polysaccharide vaccine

Individuals with properdin, C3 or late complement component deficiency (LCCD) frequently develop meningococcal disease. Vaccination of these persons has been recommended, although reports on efficacy are scarce and not conclusive. We immunized 53 complement-deficient persons, of whom 19 had properdin deficiency, seven a C3 deficiency syndrome and 27 had LCCD with the tetravalent (ACYW) meningococcal capsular polysaccharide vaccine. Serological studies were performed in 43 of them. As controls 25 non-complement-deficient relatives of the complement-deficient vaccinees and 21 healthy non-related controls were vaccinated. Post-vaccination, complement-deficient individuals and controls developed a significant immunoglobulin-specific antibody response to capsular polysaccharides group A, C, Y, W135, but a great individual variation was noticed. Also, the proportion of vaccinees of the various vaccinated groups with a significant increase in bactericidal titre (assayed with heterologous complement) was similar. Opsonization of meningococci A and W135 with sera of the 20 LCCD individuals yielded in 11 (55%) and eight (40%) sera a significant increase of phagocytic activity after vaccination, respectively. Despite vaccination, four complement-deficient patients experienced six episodes of meningococcal disease in the 6 years post-vaccination. Four episodes were due to serogroup B, not included in the vaccine. Despite good response to serogroup Y upon vaccination, disease due to serogroup Y occurred in two C8beta-deficient patients, 3.5 and 5 years post-vaccination. These results support the recommendation to vaccinate complement-deficient individuals and to revaccinate them every 3 years.

Endotoxin release and cytokine production in acute and chronic meningococcaemia

Chronic meningococcaemia is a relatively benign manifestation of meningococcal disease. Whether bacterial virulence factors are responsible for this benign course has not been studied. We compared the in vitro endotoxin-liberating ability and cytokine-inducing potential of 31 Neisseria meninigitidis isolates obtained from children with acute septic shock with that of nine isolates obtained from patients with chronic meningococcaemia and 12 isolates obtained from carriers with respiratory symptoms. The median endotoxin level released in vitro after 3 h of incubation was significantly higher for isolates causing septic shock compared with isolates from the other two groups (P=0.01 and 0.02, Mann-Whitney test). This was not explained by differences in bacterial growth rate in vitro. The median IL-6 levels in whole blood ex vivo after 4 h of incubation were also significantly lower for isolates causing chronic meningococcaemia (P=0.04, Mann-Whitney test). The endotoxin and cytokine levels measured on admission in the 31 children with acute meningococcal septic shock showed a 1000-fold variation. No relationship was established between the amount of endotoxin released by the causative microorganisms in vitro and the endotoxin or cytokine levels in the corresponding 31 children. These results suggest a diminished bacterial virulence for isolates causing chronic meningococcaemia. However, other factors than the endotoxin-releasing potential of the microorganism involved are responsible for the wide variation in endotoxin and therefore cytokine levels in patients with acute meningococcal septic shock.