Total and functional antibody response to a quadrivalent meningococcal polysaccharide vaccine among children

Should we vaccinate the better seroconverters or the most vulnerable? Game changing insights for COVID-19 vaccine prioritization policies

Background

With the rapid rise in COVID 19 cases incomparable to the number of vaccinations available, there has been a demand to prioritize the older age groups receiving the vaccine as they have more risk of morbidity and mortality and thus better outcome from vaccination.

Main body

Some studies showed a lower seroconversion rate in older group patients; thus, we discuss the necessity to reprioritize vaccinations to younger age groups who have better seroconversion rates, but we may face some ethical dilemma that could hinder our hypothesis. Decreased seroconversion rates in adults are attributable to immuno-senescence which involves a decrease in humoral and cellular-mediated immunity with age. Despite this fact, there remains some ethical dilemma that can hinder widespread vaccination of younger generations, the most important of which is the unknown long-term effects of COVID-19 vaccines due their fast-tracking under the pressure of the pandemic.

Short conclusion

Prioritizing children vaccination against COVID-19 seems an interesting strategy that can help in containing the pandemic. Resolving some ethical dilemma needs to be done before implementing such strategy.

Different Long-Term Duration of Seroprotection against Neisseria meningitidis in Adolescents and Middle-Aged Adults after a Single Meningococcal ACWY Conjugate Vaccination in The Netherlands

Neisseria meningitidis is often asymptomatically carried in the nasopharynx but may cause invasive meningococcal disease, leading to morbidity and mortality. Meningococcal conjugate vaccinations induce functional protective antibodies against capsular antigens, but seroprotection wanes over time. We measured functional antibody titers five years after administration of a single dose of the meningococcal ACWY-polysaccharide-specific tetanus toxoid-conjugated (MenACWY-TT) vaccine in adolescents and middle-aged adults in the Netherlands, using the serum bactericidal antibody with baby rabbit complement (rSBA) assay. Protection was defined as rSBA titer ≥8. The meningococcal ACWY-specific serum IgG concentrations were measured with a multiplex immunoassay. Duration of protection was estimated by a bi-exponential decay model. Sufficient protection for MenC, MenW, and MenY was achieved in 94–96% of the adolescents five years postvaccination, but, in middle-aged adults, only in 32% for MenC, 65% for MenW and 71% for MenY. Median duration of protection for MenCWY was 4, 14, and 21 years, respectively, in middle-aged adults, while, in adolescents, it was 32, 98, and 33 years. Our findings suggest that adolescents, primed in early childhood with MenC conjugate vaccination, remain sufficiently protected after a single dose of MenACWY-TT vaccine. Middle-aged adults without priming vaccination show fast waning of antibodies, particularly MenC, for which protection is lost after four years.

Carbohydrates in Vaccine Development

Despite advances in the development of new vaccines, there are still some diseases with no vaccine solutions. Therefore, further efforts are required to more comprehensively discern the different antigenic components of these microorganisms on a molecular level. This review summarizes advancement in the development of new carbohydrate-based vaccines. Following traditional vaccine counterparts, the carbohydrate-based vaccines introduced a new approach in fighting infectious diseases. Carbohydrates have played various roles in the development of carbohydrate-based vaccines, which are described in this review, including carbohydrates acting as antigens, carriers or targeting moieties. Carbohydrate-based vaccines against infectious diseases, such as group A streptococcus, meningococcal meningitis and human immunodeficiency virus, are also discussed. A number of carbohydrate- based vaccines, such as Pneumovax 23, Menveo and Pentacel, have been successfully marketed in the past few years and there is a promising standpoint for many more to come in the near future.

Technological Microbiology: Development and Applications

Over thousands of years, modernization could be predicted for the use of microorganisms in the production of foods and beverages. However, the current accelerated pace of new food production is due to the rapid incorporation of biotechnological techniques that allow the rapid identification of new molecules and microorganisms or even the genetic improvement of known species. At no other time in history have microorganisms been so present in areas such as agriculture and medicine, except as recognized villains. Currently, however, beneficial microorganisms such as plant growth promoters and phytopathogen controllers are required by various agricultural crops, and many species are being used as biofactories of important pharmacological molecules. The use of biofactories does not end there: microorganisms have been explored for the synthesis of diverse chemicals, fuel molecules, and industrial polymers, and strains environmentally important due to their biodecomposing or biosorption capacity have gained interest in research laboratories and in industrial activities. We call this new microbiology Technological Microbiology, and we believe that complex techniques, such as heterologous expression and metabolic engineering, can be increasingly incorporated into this applied science, allowing the generation of new and improved products and services.

Meningococcal serogroup B vaccines: Estimating breadth of coverage

Neisseria meningitidis serogroup B (MenB) is an important cause of invasive meningococcal disease. The development of safe and effective vaccines with activity across the diversity of MenB strains has been challenging. While capsular polysaccharide conjugate vaccines have been highly successful in the prevention of disease due to meningococcal serogroups A, C, W, and Y, this approach has not been possible for MenB owing to the poor immunogenicity of the MenB capsular polysaccharide. Vaccines based on outer membrane vesicles have been successful in the prevention of invasive MenB disease caused by the single epidemic strain from which they were derived, but they do not confer broad protection against diverse MenB strains. Thus, alternative approaches to vaccine development have been pursued to identify vaccine antigens that can provide broad protection against the epidemiologic and antigenic diversity of invasive MenB strains. Human factor H binding protein (fHBP) was found to be such an antigen, as it is expressed on nearly all invasive disease strains of MenB and can induce bactericidal responses against diverse MenB strains. A bivalent vaccine (Trumenba®, MenB-FHbp, bivalent rLP2086) composed of equal amounts of 2 fHBP variants from each of the 2 immunologically diverse subfamilies of fHBP (subfamilies A and B) was the first MenB vaccine licensed in the United States under an accelerated approval pathway for prevention of invasive MenB disease. Due to the relatively low incidence of meningococcal disease, demonstration of vaccine efficacy for the purposes of licensure of bivalent rLP2086 was based on vaccine-elicited bactericidal activity as a surrogate marker of efficacy, as measured in vitro by the serum bactericidal assay using human complement. Because bacterial surface proteins such as fHBP are antigenically variable, an important component for evaluation and licensure of bivalent rLP2086 included stringent criteria for assessment of breadth of coverage across antigenically diverse and epidemiologically important MenB strains. This review describes the rigorous approach used to assess broad coverage of bivalent rLP2086. Alternative nonfunctional assays proposed for assessing vaccine coverage are also discussed.

Entirely Carbohydrate-Based Vaccines: An Emerging Field for Specific and Selective Immune Responses

Carbohydrates are regarded as promising targets for vaccine development against infectious disease because cell surface glycans on many infectious agents are attributed to playing an important role in pathogenesis. In addition, oncogenic transformation of normal cells, in many cases, is associated with aberrant glycosylation of the cell surface glycan generating tumor associated carbohydrate antigens (TACAs). Technological advances in glycobiology have added a new dimension to immunotherapy when considering carbohydrates as key targets in developing safe and effective vaccines to combat cancer, bacterial infections, viral infections, etc. Many consider effective vaccines induce T-cell dependent immunity with satisfactory levels of immunological memory that preclude recurrence. Unfortunately, carbohydrates alone are poorly immunogenic as they do not bind strongly to the MHCII complex and thus fail to elicit T-cell immunity. To increase immunogenicity, carbohydrates have been conjugated to carrier proteins, which sometimes can impede carbohydrate specific immunity as peptide-based immune responses can negate antibodies directed at the targeted carbohydrate antigens. To overcome many challenges in using carbohydrate-based vaccine design and development approaches targeting cancer and other diseases, zwitterionic polysaccharides (ZPSs), isolated from the capsule of commensal anaerobic bacteria, will be discussed as promising carriers of carbohydrate antigens to achieve desired immunological responses.

The immunogenicity and impact on nasopharyngeal carriage of fewer doses of conjugate pneumococcal vaccine immunization schedule

The immunogenicity and impact on carriage of fewer doses of pneumococcal conjugate vaccine (PCV7) followed by booster with pneumococcal polysaccharide vaccine (PPV) were investigated. 684 infants were assigned randomly to one of the three groups that received one (A), two (B) or three (C) doses of PCV7 between 2 and 4 months of age, plus PPV at 10 months. Following primary vaccination protective antibody titers of >0.35 μg/ml against the PCV7 serotypes combined increased significantly with the number of PCV7 doses, 44% vs. 77% vs. 94% (p<0.001), and correlated positively with the opsonophagocytic indices, but negatively with nasopharyngeal carriage of pneumococcus. The differences in antibody responses and pneumococcal carriage between the groups diminished following booster with PPV, implying that administration of one or two doses of PCV7, with a booster dose of PPV might lower the cost of protection against IPD in young children in resource poor countries.

Binding of complement factor H (fH) to Neisseria meningitidis is specific for human fH and inhibits complement activation by rat and rabbit sera

Complement factor H (fH), a molecule that downregulates complement activation, binds to Neisseria meningitidis and increases resistance to serum bactericidal activity. We investigated the species specificity of fH binding and the effect of human fH on downregulating rat (relevant for animal models) and rabbit (relevant for vaccine evaluation) complement activation. Binding to N. meningitidis was specific for human fH (low for chimpanzee fH and not detected with fH from lower primates). The addition of human fH decreased rat and rabbit C3 deposition on the bacterial surface and decreased group C bactericidal titers measured with rabbit complement 10- to 60-fold in heat-inactivated sera from human vaccinees. Administration of human fH to infant rats challenged with group B strain H44/76 resulted in an fH dose-dependent increase in CFU/ml of bacteria in blood 8 h later (P < 0.02). At the highest fH dose, 50 microg/rat, the geometric mean number of CFU per ml was higher than that in control animals (1,050 versus 43 [P < 0.005]). The data underscore the importance of binding of human fH for survival of N. meningitidis in vitro and in vivo. The species specificity of binding of human fH adds another mechanism toward our understanding of why N. meningitidis is strictly a human pathogen.

Epitope specificities of the group Y and W-135 polysaccharides of Neisseria meningitidis

Previous studies have identified the length dependency of several polysaccharide (PS) protective epitopes. We have investigated whether meningococcal polysaccharides Y and W-135 possess such epitopes. Oligosaccharides (OSs) consisting of one or more disaccharide repeating units (RU) were derived from the capsular PSs of group Y and W-135 meningococci (GYMP and GWMP, respectively) by mild acid hydrolysis. The relative affinities of anticapsular antibodies binding to derivative OSs of different chain lengths were measured in inhibition enzyme-linked immunosorbent assays. As OS size increased from two to three RU, there was a notable increase in binding inhibition of rabbit anti-group Y antiserum. This pattern of antibody binding inhibition was also observed for rabbit antiserum to group W-135, though the inhibition increase was much more pronounced. In the cases of both OS species, the concentration of inhibiting antigen required to achieve 50% inhibition of rabbit immunoglobulin binding increased progressively as the inhibiting disaccharide chain length increased from 1 RU through greater than 50 RU. These data suggest that antibodies directed against both of these meningococcal PSs recognize conformational epitopes only fully expressed in higher-molecular-weight forms of these antigens.

Use of meningococcal vaccines in the United States

In January 2005, Food and Drug Administration licensed a new tetravalent (serogroups A, C, Y, W-135) meningococcal conjugate vaccine ([MCV4] Menactra) for use in persons 11-55 years of age. In February 2005, CDC's Advisory Committee on Immunization Practices (ACIP) recommended routine vaccination of adolescents and college freshmen living in dormitories with MCV4. The manufacturer started shipments of MCV4 in March 2005. MCV4 should become a key addition to existing meningococcal disease prevention measures.

Safety and efficacy of meningococcal c vaccination in juvenile idiopathic arthritis

OBJECTIVE

To determine whether vaccinations aggravate the course of autoimmune diseases such as juvenile idiopathic arthritis (JIA) and whether the immune response to vaccinations may be hampered by immunosuppressive therapy for the underlying disease.

METHODS

In this multicenter cohort study, 234 patients with JIA (ages 1-19 years) were vaccinated with meningococcal serogroup C (MenC) conjugate to protect against serogroup C disease (caused by Neisseria meningitidis). Patients were followed up for disease activity for 1 year, from 6 months before until 6 months after vaccination. IgG antibody titers against MenC polysaccharide and the tetanus carrier protein were determined by enzyme-linked immunosorbent assay and toxin binding inhibition assay, respectively. A serum bactericidal assay was performed to determine the function of the anti-MenC antibodies.

RESULTS

No change in values for any of the 6 components of the core set criteria for juvenile arthritis disease activity was seen after MenC vaccination. Moreover, no increase in the frequency of disease relapse was detected. Mean anti-MenC IgG concentrations in JIA patients rose significantly within 6-12 weeks after vaccination. Of 157 patients tested, 153 were able to mount anti-MenC IgG serum levels >2 micro g/ml, including patients receiving highly immunosuppressive medication. The 4 patients with a lower anti-MenC antibody response displayed sufficient bactericidal activity despite receiving highly immunosuppressive medication.

CONCLUSION

The MenC conjugate vaccine does not aggravate JIA disease activity or increase relapse frequency and results in adequate antibody levels, even in patients receiving highly immunosuppressive medication. Therefore, patients with JIA can be vaccinated safely and effectively with the MenC conjugate.

Prospective survey on carriage of Neisseria meningitidis and protective immunity to meningococci in schoolchildren in Niamey (Niger): focus on serogroup W135

We investigated the carriage of serogroup W135 meningococci and its relationship with protective immunity in Niamey. Between February and May 2003, three oropharyngeal swabs and two serum samples were each taken from 287 school children. Serogroup W135 isolates were obtained from 8.9% of children. Specific IgG > or = 2 microg/ml using ELISA or serum bactericidal assay (SBA) titre > or = 8 were supposed to represent the protective immunity to a serogroup. The proportion of children with serogroup W135-specific IgG > or = 2 microg/ml increased significantly during follow-up (13.9% to 19.1%), but not the proportion of those with SBA titre > or = 8 (10.1% to 11.6%). At the end of the follow-up, we observed a significant association between carriage of serogroup W135 strains and presumed protective immunity to this serogroup, using either ELISA or SBA. Among 240 children having an initial SBA titre < 8, 20 carried serogroup W135 strains at least once. In May, 25% of carriers had an SBA titre > or = 8, vs. 2.3% of non-carriers. For ELISA, 230 children had specific IgG < 2 microg/ml in February, with 22 having at least one swab positive for serogroup W135 meningococci later. In May, 45.5% of them had specific IgG > or = 2 microg/ml vs. 5.3% among non-carriers.

Naturally-acquired immunity to Neisseria meningitidis group A

Group A meningococcal disease is epidemic in Sudan, less common in Uganda, a country bordering the "meningitis belt," and rare in North America. The basis of naturally-acquired group A immunity is unknown but in North America protection has been attributed to a high prevalence of serum anticapsular antibodies elicited by cross-reacting bacteria. We measured group A anticapsular antibody concentrations and bactericidal titers in sera from 236 adults (47 from the Sudan obtained at the height of a group A epidemic, 57 from Uganda, and 132 from North America). Anticapsular antibody concentrations were higher in Sudanese sera than in North American or Ugandan sera (geometric mean of 31.5 versus 5.4 and 5.3 microg/ml, respectively, P < 0.0001). Bactericidal titers of > or =1:4 (presumed to be a protective titer when measured with human complement) were detected in 66% of Sudanese sera as compared with 27 and 23%, respectively, of North American and Ugandan sera (P < 0.0001). Bactericidal activity was inhibited by group A polysaccharide in 58% of the Sudanese bactericidal sera as compared to 17 and 6% of North America and Ugandan bactericidal sera (P < 0.0005). Approximately 50% of non-bactericidal Sudanese sera had high IgA anticapsular antibody concentrations, which were rare in bactericidal Sudanese sera. Thus, serum anticapsular antibodies and bactericidal activity are prevalent in Sudanese exposed to a group A epidemic. Cross-reacting group A anticapsular antibodies are prevalent in North American and Ugandan sera, but bactericidal activity is infrequent and when present is largely directed at non-capsular antigens.

Mucosal immunology of vaccines against pathogenic nasopharyngeal bacteria

The introduction of Haemophilus influenzae type b conjugate vaccines during the 1990s was followed by dramatic decreases both in the incidence of Haemophilus influenzae type b related invasive disease and in nasopharyngeal carriage of the organism. The extent of this effect has been influenced by the fact that Haemophilus influenzae type b conjugate vaccines reduce nasopharyngeal carriage and induce herd immunity. Based on the success of Haemophilus influenzae type b conjugate vaccines, chemical conjugation has been applied to the development of pneumococcal and meningococcal polysaccharide conjugate vaccines. Evidence has begun to accumulate that these new polysaccharide based conjugate vaccines can also reduce nasopharyngeal carriage and can induce immune responses at the local mucosal level, which may be responsible for these effects. This article reviews recent studies on mucosal immune responses induced by polysaccharide based vaccines and some protein vaccine antigens against several pathogenic nasopharyngeal bacteria, and discusses the mechanisms and functions of these immune responses that may help our understanding of mucosal immune responses to both immunisation and infection.

Dosage escalation, safety and immunogenicity study of four dosages of a tetravalent meninogococcal polysaccharide diphtheria toxoid conjugate vaccine in infants

BACKGROUND

Young children have the highest incidence of meningococcal infection. Approximately 50% of disease in United States children less than 2 years of age is caused by serogroups C and Y. In the developing world, serogroups A and W-135 cause outbreaks and epidemics of infection.

METHODS

Three groups of 30 infants were enrolled. The first group of infants was given 3 doses of a quadrivalent (group A, C, Y, W-135) polysaccharide meningococcal vaccine conjugated to diphtheria toxoid (MCV-4) at a dosage of 1 microg of each serogroup polysaccharide. The second group of infants was given MCV-4 at a dosage of 4 microg, and the last group of children received a 10-microg dosage. Vaccinations were given at 2, 4 and 6 months of age.A subset of these children was vaccinated at 15 to 18 months of age with licensed meningococcal polysaccharide (A, C, Y, W-135) vaccine. Serum bactericidal antibody (SBA) titers were measured with baby rabbit complement.

RESULTS

The proportion of infants with local reactions increased significantly with increasing dosages after Injection 1 and 3. Approximately 1 month after completion of the primary series, the proportion of infants with an SBA titer > or = 1/8 ranged from 54 to 92%, depending on the serogroup and dose of polysaccharide contained in the vaccine. The SBA geometric mean titer varied from 17.4 to 101.6. There was no statistically significant difference between the SBA responses among the 3 dosage groups. After vaccination with polysaccharide vaccine at 15 to 18 months of age, mean fold increases in SBA of 4.9 to 170.3 were observed, suggesting an anamnestic response.

CONCLUSIONS

MCV-4 appears to have a reactogenicity profile acceptable to parents and health care providers. It was only modestly immunogenic in infants, but it appeared to prime the immune system of the majority of infants given three doses in infancy. There is no statistically significant immunologic advantage conferred by increasing the dosage beyond 4 microg/ml, and local reactions are more frequent after the 10-microg/ml dosage.

Mucosal immune responses to capsular pneumococcal polysaccharides in immunized preschool children and controls with similar nasal pneumococcal colonization rates

BACKGROUND

Immunization with conjugate pneumococcal vaccines induces significant primary and memory IgG anti-polysaccharide (PS) responses in serum. It can also induce mucosal responses in infants especially after a polysaccharide booster. However, it is unclear whether it can prime for mucosal memory responses on nasal exposure to pneumococcus, which may be important in protection against pneumococcal invasion and/or carriage.

METHOD

IgA and IgG to serotypes 4, 6B, 9V, 14, 18C, 19F and 23F (conjugate vaccine serotypes), 1 and 3 (nonvaccine serotypes) capsular PS were measured by immunoassay in saliva from 2- to 5-year-old children previously given three doses of 7-valent pneumococcal conjugate vaccine in infancy, followed by 23-valent PS vaccine at 13 months and from unvaccinated controls of similar age and sex. Salivary antibody responses were analyzed in relation to carriage of pneumococci assessed by bacterial culture of nasopharyngeal swab samples collected in the summer and winter of the year 2000.

RESULTS

Rates of detectable IgG antibodies to all vaccine serotypes except 23F were higher in subjects than in controls. No such differences were observed for IgA antibodies except for serotype 6B. Nasal colonization rates were similar, and in both groups mucosal IgA responses were more common and larger than IgG responses.

CONCLUSIONS

The mucosal anti-capsular IgA responses observed could develop in response to colonization in preschool children, regardless of vaccination status, and contribute to the falling carriage rates observed with increasing age.

Meningococcal immunology

There is a major need for an effective vaccine against serogroup B disease. The long-term efficacy of the serogroups A, C, Y and W135 conjugate vaccines and the need for booster vaccines has to be determined, as does the effect of changing epidemiology in the United States and worldwide. Control of serogroup A disease in sub-Saharan Africa is a major challenge.

Induction of a protective capsular polysaccharide antibody response to a multiepitope DNA vaccine encoding a peptide mimic of meningococcal serogroup C capsular polysaccharide

Systemic infection by encapsulated organisms, such as Neisseria meningitidis, is a major cause of morbidity and mortality worldwide, especially in individuals less than 2 years of age. Antibodies directed at the capsular polysaccharide are shown to be protective against disease by inducing complement-dependent bactericidal activity. The current polysaccharide vaccine has been shown to be poorly immunogenic in high-risk groups and this is probably related to its T-independent properties. An alternative approach to eliciting a T-dependent serum immunoglobulin G (IgG) antibody response to encapsulated pathogens is DNA vaccination. We assessed the immunogenicity of a multiepitope DNA vaccine encoding a T-cell helper epitope and a peptide mimic of N. meningitidis serogroup C. The DNA construct induced a significant anti-polysaccharide antibody response that was bactericidal. Mice immunized with the DNA construct were subsequently protected against challenge with a lethal dose of N. meningitidis serogroup C.

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.

Age-related disparity in functional activities of human group C serum anticapsular antibodies elicited by meningococcal polysaccharide vaccine

Serum bactericidal activity confers protection against meningococcal disease, but it is not known whether vaccine-induced anticapsular antibodies that lack bactericidal activity are protective. We developed an infant rat challenge model using a naturally occurring O-acetylated strain of Neisseria meningitidis group C and a strain that was negative for O acetylation (OAc). Rats 4 to 7 days of age inoculated intraperitoneally (i.p.) with approximately 10(3) CFU of either strain developed >5 x 10(5) CFU/ml of blood obtained 18 h later. Dilutions of preimmunization sera given i.p. 2 h before the bacterial challenge had no effect on bacteremia, whereas group C anticapsular antibody in sera from adults immunized with meningococcal polysaccharide vaccine conferred complete or partial (>99% decrease in CFU per milliliter of blood) protection against the OAc-positive or OAc-negative strain, respectively, at antibody doses as low as 0.04 micro g/rat. Anticapsular antibody at doses fivefold higher (0.18 to 0.2 micro g/rat) in pooled sera from children immunized at a mean age of 2.6 years failed to protect rats, but antibody at the same or fivefold-lower dose in a serum pool from a group of children immunized at 4 years of age gave complete or partial protection. Protective activity was observed with some serum pools that lacked detectable complement-mediated bactericidal activity (titers < 1:4) and correlated with increasing antibody avidity. Thus, not only does the magnitude of the group C antibody response to meningococcal polysaccharide vaccine increase with increasing age but there are also age-related affects on antibody functional activity such that higher serum concentrations of vaccine-induced antibody are required for protection of immunized children than for immunized adults.

Vaccines for the prevention of meningococcal disease in children

Neisseria meningitidis is one of the most feared infections in pediatrics as the result of its rapid progression, high fatality rate, and frequent occurrence of sequelae. The 5 major meningococcal serogroups associated with disease are A, B, C, Y, and W-135. Currently available polysaccharide vaccines are effective in preventing disease caused by serogroups A, C, Y, and W-135 in older children and adults but do not elicit good long-term protection in young children. Vaccines that protect against serogroup B disease are still in development. As with the Haemophilus influenzae type b and pneumococcal polysaccharide vaccines, conjugation of the polysaccharide vaccine to a protein carrier dramatically changes vaccine characteristics, with resulting efficacy in infants. New meningococcal conjugate vaccines against serogroups A, C, Y, and W-135 are being developed. A serogroup C conjugate vaccine has been introduced successfully into the routine childhood schedule in the United Kingdom. New meningococcal conjugate vaccines are likely to have a dramatic effect on the burden of meningococcal disease within the next decade.

Immunogenicity of a serogroup B meningococcal vaccine against multiple Neisseria meningitidis strains in infants

BACKGROUND

The serogroup B meningococcus is responsible for the majority of cases of meningococcal disease in temperate countries. Infants and young children <2 years of age are at greatest risk of disease. This study assessed the immunogenicity in infants of a serogroup B meningococcal outer membrane protein vaccine that has been used extensively in disease outbreaks in Cuba and several Latin American countries and shown to be efficacious in teenagers.

METHOD

One hundred five healthy infants entering the routine vaccination schedule in Havana, Cuba, were given either 2 or 3 doses of the serogroup B meningococcal vaccine VA-MENGOC-BC at 3.5, 5.5 and 7.5 months of age. Immune response pre- and postvaccination was determined by the conventional serum bactericidal assay (SBA), a more sensitive novel whole blood bactericidal assay (WBA) and immunoglobulin ELISA.

RESULTS

In 52 and 46% of infants >50% killing of the vaccine serogroup B strain (B:4:P1.19,15) and serogroup C strain, respectively, was demonstrated by the WBA after 2 doses of the vaccine. Serum bactericidal activity (4-fold increase in titer) was induced in only 27% against the vaccine serogroup B strain and in 14% against the serogroup C strain. The changes in WBA and SBA were mirrored by the serogroup B and C immunoglobulin ELISA. Cross-reactive immunogenicity against other (heterologous) serogroup B strains was demonstrated for one of the four further strains assessed by WBA. By age 16 to 18 months SBA, WBA and ELISA responses had declined considerably. The addition of a third dose of vaccine did not appear to significantly influence immunogenicity at 17 months of age.

CONCLUSION

The serogroup B outer membrane protein vaccine VA-MENGOC-BC induces a demonstrable immune response in infants against both the serogroup B vaccine strain and against a serogroup C strain. Cross-reactive immunogenicity against other (heterologous) serogroup B strains is limited in this age group.

Safety and immunogenicity of three lots of meningococcal serogroup C conjugate vaccine administered at 2, 3 and 4 months of age

The reactogenicity and immunogenicity of meningococcal serogroup C conjugate (MenC) vaccine was assessed in 322 infants vaccinated at 2, 3, and 4 months of age, with concomitant administration of mixed diphtheria-tetanus-whole-cell pertussis vaccine and Haemophilus influenzae type b conjugate vaccine (DTwP-Hib) and oral polio vaccine. All infants in whom post-vaccination meningococcal C anticapsular IgG levels were assayed (n = 265) attained > or = 2 microg ml(-1). Serum bactericidal titres were assayed for a proportion of subjects (n = 171), 98% of whom obtained a reciprocal titres > or = 8. Local reactions were less frequent at the MenC injection site than at the DTP-Hib site. Systemic events were frequent, but consistent with established DTwP-Hib experience. The study demonstrates that MenC vaccine is immunogenic and well tolerated in infants at manufacturing scale production levels.

Dramatic decline of serogroup C meningococcal disease incidence in Catalonia (Spain) 24 months after a mass vaccination programme of children and young people

STUDY OBJECTIVES

The objective of this study was to evaluate the effectiveness of a mass vaccination programme carried out in Catalonia (Spain) in the last quarter of 1997 in response to an upsurge of serogroup C meningococcal disease (SCMD).

DESIGN

Vaccination coverage in the 18 month to 19 years age group was investigated by means of a specific vaccination register. Vaccination effectiveness was calculated using the prospective cohort method. Cases of SCMD were identified on the basis of compulsory reporting and microbiological notification by hospital laboratories. Vaccination histories were investigated in all cases. Unadjusted and age adjusted vaccination effectiveness referred to the time of vaccination and the corresponding 95% confidence intervals (CI) were estimated at 6, 12, 18 and 24 months of follow up.

SETTING

All population aged 18 months to 19 years of Catalonia.

MAIN RESULTS

A total of seven cases of SCMD were detected at six months of follow up (one in the vaccinated cohort), 12 cases at 12 months (one in the vaccinated cohort), 19 cases at 18 months (two in the vaccinated cohort) and 24 at 24 months (two in the vaccinated cohort). The age adjusted effectiveness was 84% (95%CI 30, 97) at six months, 92% (95%CI 63, 98) at 12 months, 92% (95% CI 71, 98) at 18 months and 94% (95%CI 78, 98) at 24 months. In the target population, cases have been reduced by more than two thirds (68%) two years after the vaccination programme. In the total population the reduction was 43%.

CONCLUSION

Vaccination effectiveness has been high in Catalonia, with a dramatic reduction in disease incidence in the vaccinated cohort accompanied by a relevant reduction in the overall population. Given that vaccination coverage was only 54.6%, it may be supposed that this vaccination effectiveness is attributable, in part, to the herd immunity conferred by the vaccine.

Safety and immunogenicity of four doses of Neisseria meningitidis group C vaccine conjugated to CRM197 in United States infants

BACKGROUND

Following widespread use of conjugate pneumococcal vaccine, Neisseria meningitidis likely will become the leading cause of bacterial sepsis and meningitis in US children. This report describes the safety and immunogenicity in US children of four consecutive doses of a meningococcal group C vaccine conjugated to CRM197 via reductive amination (MnCC).

METHODS

One hundred six healthy 2-month-old infants received MnCC at 2, 4 and 6 months of age in a randomized, controlled double blind study; children in the other treatment arm were given a 7-valent conjugate pneumococcal vaccine. Parents reenrolled 64 of these children at 12 to 15 months to receive a fourth dose of MnCC. Routine childhood vaccines, including DTP, were coadministered. Temperatures and symptoms were recorded for 3 days after each immunization. Serum enzyme-linked immunosorbent assay IgG and bactericidal antibodies were measured prevaccination and before and 1 month after Doses 3 and 4.

RESULTS

Moderate to severe local reactions, defined as erythema or induration > or =2.4 cm or pain that interfered with limb movement was reported after 0 to 3.2% of MnCC injections, depending on the reaction and dose. Fever occurred in 23 to 37% of children, but the contribution of MnCC to the febrile reactions is unknown. Geometric mean concentrations of IgG antibody to group C meningococcal polysaccharide were 3.72 microg/ml after Dose 3 and 8.03 microg/ml after the booster. Geometric mean functional serum bactericidal antibody titers after Doses 3 and 4 were 1:463 and 1:2341, respectively. One hundred percent of children had a serum bactericidal antibody titer of > or =1:64 after three doses and > or = 1:128 after the booster.

CONCLUSIONS

The MnCC vaccine had an acceptable safety profile and generated high titers of bactericidal antibody in immunized US infants and toddlers. It appears to be an attractive candidate vaccine for the prevention of serogroup C meningococcal disease in young children.

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.

Seroconversion and duration of immunity after vaccination against group C meningococcal infection in young children

An increase in the incidence of group C meningococcal disease was observed in the Murcia Region (Spain) during 1996-1997. In September 1997, a massive vaccination campaign was implemented among the population aged 18 months to 19 years. The aim of this study was to assess the seroconversion rate of children aged 18-59 months and the persistence of immune response 1 year after vaccination. A total of 296 children were included. Blood samples were obtained before vaccination and 1 month and 1 year after vaccination. Three point seven percent of the children had bactericidal antibody titres of >/=1:8 before vaccination. One month after vaccination seroconversion was 63.7%, with a growing trend related to age at vaccination (p<0.0001). The increase in antibody titres was shown to be quantitatively greater above the age of 36 months (p<0.0001). One year after vaccination only 4.3% of the children who initially seroconverted still had bactericidal activity. Seroconversion in children under 5 increases with age but antibodies decline rapidly in the year following vaccination.

Immunogenicity and reactogenicity of a group C meningococcal conjugate vaccine compared with a group A+C meningococcal polysaccharide vaccine in adolescents in a randomised observer-blind controlled trial

This study evaluated the immunogenicity and reactogenicity of a group C meningococcal conjugate vaccine (MenC) compared with a group A+C meningococcal polysaccharide vaccine (MenPS) in healthy adolescents. Subjects were randomised to receive one dose of either MenC (n=92) or MenPS (n=90). Group C meningococcal IgG antibody concentrations and bactericidal titres were higher in the MenC group than the MenPS group at 1 month (22.8 U/ml vs 4.0 U/ml, p<0.001, and 87 vs 20, p<0.001, respectively) and 12 months (6.1 U/ml vs 3.0 U/ml, p<0.001, and 81.3 vs 20.2, p<0.001, respectively). No differences in post immunisation reaction rates were noted between the two vaccinated groups. This study demonstrated the safety and enhanced immunogenicity of the candidate meningococcal conjugate vaccine as compared with the licensed polysaccharide vaccine in adolescents.

Meningococcal serogroup C-specific IgG antibody responses and serum bactericidal titres in children following vaccination with a meningococcal A/C polysaccharide vaccine

In the UK, a co-ordinated series of phase II studies is being undertaken with meningococcal serogroup C conjugate (MCC) vaccines. The use of meningococcal A/C polysaccharide (MACP) vaccines in control arms in young children has been avoided because of the well recognised short comings of these vaccines. Following a cluster of serogroup C disease centred on a day nursery, intervention by MACP vaccination was performed as an outbreak control measure. Using this cohort, serogroup C-specific IgG ELISA and serum bactericidal assays (SBA) were performed using both de-O-acetylated (Oac(-)) and acetylated (Oac(+)) serogroup C antigen, the measurement of primarily high avidity antibody and using baby rabbit or human complement in the SBA. The effect of subject age (either less than or greater than 2 years of age) was assessed for the different assays and significant differences (P<0.05) were found using both antigen sources in the high avidity ELISA and in the rabbit complement SBA but not in the standard ELISA. When assessing results from different studies it is important that methodologies utilised allow such comparisons since the choice of reagents can have a profound influence. The importance of standardised assays is paramount at a time where immunogenicity trials are replacing efficacy trials for the introduction of MCC vaccines.

Mucosal immune responses to meningococcal group C conjugate and group A and C polysaccharide vaccines in adolescents

Previous studies in children have shown that Haemophilus influenzae type b (Hib) polysaccharide conjugate vaccines can reduce nasopharyngeal carriage of H. influenzae and provide herd immunity and suggest that this effect is mediated through mucosal antibodies. As this phenomenon may operate in other invasive bacterial infections which are propagated by nasopharyngeal carriage, mucosal antibody responses to meningococcal C conjugate and A/C polysaccharide vaccines were investigated. A total of 106 school children aged 11 to 17 years were randomized to receive a single dose of either conjugate or polysaccharide vaccine in an observer-blind study. Before and at 1, 6, and 12 months after immunization, samples of unstimulated saliva were collected and assayed by enzyme-linked immunosorbent assay for group C polysaccharide-specific immunoglobulin A (IgA), IgA1, IgA2 and secretory component, IgG antibodies, and total IgG and IgA. A subset of serum samples were also assayed for specific IgA and IgG antibodies. The concentrations of specific IgA and IgG in saliva were expressed both as nanograms per milliliter and as nanograms per microgram of total IgA or IgG. One month after immunization, significant increases in antibody titers (both IgA and IgG) were observed in saliva in both groups. There were significant subsequent falls in antibody titers by 6 months. Anti-meningococcal C-specific secretory component and IgA antibody titers were closely correlated (r = 0.85, P < 0.001), but there was no significant correlation between salivary and serum IgA titers, suggesting that IgA antibodies are locally produced. Significant correlation was found between salivary and serum IgG titers (r = 0.52, P < 0.01), suggesting that salivary IgG may be serum derived. Compared with polysaccharide vaccine, the conjugate vaccine induced significantly higher salivary IgG responses (P < 0.05), although there were no significant differences between salivary IgA responses to the two vaccines. The conjugate vaccine induced greater salivary IgG responses than a polysaccharide vaccine. Both vaccines induced significant salivary IgA antibodies. Further studies are needed to establish the functional significance of these mucosal responses.

Phagocytic killing and antibody response during the first year after tetravalent meningococcal vaccine in complement-deficient and in normal individuals

Seven individuals with late complement component (LCC) deficiency and seven control subjects were vaccinated with tetravalent meningococcal vaccine. The response to vaccination was evaluated by measuring the antibody titer and the phagocyte killing of the bacteria, before, 5-7 weeks, and 12-14 months after vaccination. Prior to vaccination, no phagocytic killing and a low titer of antibody was found in the LCC-deficient group and a low killing (mean of 40-58%, according to the serogroup) in normal controls. The phagocytic killing increased significantly 5-7 weeks after vaccination. However, while in normal controls the phagocytic killing was close to 100% after 5-7 weeks and decreased only slightly during the first year, the mean killing of the various meningococcal subgroups in LCC-deficient individuals was 70-89% and dropped to only 53-71% one year after vaccination. Six weeks after vaccination the mean antimeningococcal antibody titer increased similarly in the sera of LCC-deficient patients and controls. One year after vaccination the controls maintained the high concentration, while the LCC-deficient patients had tendency toward a decrease. In addition, the interpersonal variability of the antibody concentration, both in LCC-deficient individuals and in normal controls, was much higher than the phagocytic killing, with only a very mild increase in some individuals. Thus, it is possible that in spite of adequate increase of antimeningococcal antibody titer after vaccination of LCC-deficient individuals their immunity against the bacteria may not be optimal. Our data show also that phagocytic killing of meningococci is probably a more consistent assay than antibody titer levels for antimeningococcal immunity, especially in LCC-deficient patients.

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.

Prophylaxis of bacterial meningitis

A comprehensive review of all major agents causing bacterial meningitis--meningococcus of the groups A, B, C, W135, and Y, pneumococcus, and Haemophilus influenzae type B (Hib)--is done in terms of preventing them by chemoprophylaxis or vaccination. Some evidence suggests that the group B meningococcal disease may also be very likely preventable by a vaccine that is already available. Excellent Hib conjugates use a technique that is expected to revolutionize immunoprophylaxis against most meningococcal and pneumococcal diseases in the near future. Unfortunately, the high cost of conjugate vaccines restricts their use in many poor countries.

[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.

Age-related immunogenicity of meningococcal polysaccharide vaccine in aboriginal children and adolescents living in a Northern Manitoba reserve community

OBJECTIVE

To determine the total and functional serogroup C antibody response to a quadrivalent meningococcal polysaccharide vaccine in a group of aboriginal infants, children and adolescents. A secondary objective was to determine their prevalence of meningococcal carriage.

DESIGN

Open prospective, before and after intervention study.

SUBJECTS

Aboriginal children ages 0.5 to 19.9 years, living in a single Northern community and eligible for a public health immunization campaign conducted in all Manitoba native reserve communities to control a meningococcal serogroup C, electrophoretic type (ET) 15 outbreak. No outbreak cases had occurred in the community at the time of the study.

METHODS

Total serogroup C capsular polysaccharide antibody (CPA) and functional bactericidal antibody (BA) responses were measured by enzyme-linked immunosorbent assay and bactericidal assay, respectively.

RESULTS

Neisseria meningitidis was recovered from the oropharynx of 13 (5.2%) of 249 aboriginal children including 4 (1.6%) serogroup C isolates, all with the designation C:2a:P1.2,5 ET15. Paired sera from 152 children were available for assay. For CPA the geometric mean concentrations and proportions with > or =2 microg/ml before and after immunization were 0.69, 18% and 12.3, 96%, respectively. A significant increase in serum CPA was achieved by children of all ages, with the greatest response occurring after age 11 years. Among infants < lyear old 89% achieved concentrations of > or =2 microg/ml. For BA the pre- and post-vaccine geometric mean titers were 1.02 and 45.9. The response was significantly associated with age. BA titers > or =1:8 were present, before and after immunization, respectively, in 0 and 0% of infants <1 year old, 0 and 20% of 1- to 1.4-year-olds, 0 and 50% of 1.5- to 1.9-year-olds and 1 and 100% of > or =2-year-olds.

CONCLUSION

The age-related total and functional group C meningococcal antibody response after quadrivalent polysaccharide vaccine among aboriginals is similar to that reported for Caucasian children. After age 2 all children made excellent CPA and BA responses. In the younger age groups the BA response was blunted but 82 to 95% achieved CPA titers of > or =2 microg/ml.

A modified enzyme-linked immunosorbent assay for measurement of antibody responses to meningococcal C polysaccharide that correlate with bactericidal responses

The standardized enzyme-linked immunosorbent assay (ELISA) for measurement of serum immunoglobulin G (IgG) antibody responses to meningococcal C polysaccharide has been modified to employ assay conditions that ensure specificity and favor detection primarily of high-avidity antibodies. The modified and standard assays were used to measure IgG antibody concentrations in sera of toddlers vaccinated with meningococcal polysaccharide vaccine or a meningococcal C conjugate vaccine. The results were compared to the respective complement-mediated bactericidal antibody titers. In sera obtained after one or two doses of vaccine, the correlation coefficients, r, for the results of the standard assay and bactericidal antibody titers were 0.45 and 0.29, compared to 0.85 and 0.87, respectively, for the modified assay. With the standard assay, there were no significant differences between the geometric mean antibody responses of the two vaccine groups. In contrast, with the modified assay, 5- to 20-fold higher postvaccination antibody concentrations were measured in the conjugate than in the polysaccharide group. Importantly, the results of the modified assay, but not the standard ELISA, paralleled the respective geometric mean bactericidal antibody titers. Thus, by employing conditions that favor detection of higher-avidity IgG antibody, the modified ELISA provides results that correlate closely with measurements of antibody functional activity that are thought to be important in protection against meningococcal disease.

Age-dependent Neisseria meningitidis serogroup C class-specific antibody concentrations and bactericidal titers in sera from young children from Montana immunized with a licensed polysaccharide vaccine

Neisseria meningitidis serogroup C bactericidal titers and class-specific enzyme-linked immunosorbent assay (ELISA) antibody concentrations were measured in sera from 173 children (1 to 5 years old) before and 6 weeks and 7 months following vaccination with a quadrivalent (A/C/Y/W-135) polysaccharide vaccine. The immune responses of the children were compared with those of 40 adults 6 weeks postvaccination. Both bactericidal titers and ELISA antibody concentrations were significantly higher in the adults than in the children (P < 0.05). In addition, the ratio of immunoglobulin G (IgG) to IgM was higher in the children than in the adults. With an ELISA total antibody concentration of >/=2 microg/ml used as a measure of seroconversion, >/=84% of the individuals from each age group responded to the serogroup C polysaccharide. However, with a >/=4-fold-increase in bactericidal titer used, only 18% of 1-year-olds, 32% of 2-year-olds, and 50 to 60% of 3-, 4-, and 5-year-olds seroconverted. The ELISA results suggest that >50% of all children retained >/=2 microg of total antibody per ml at 7 months postimmunization. However, the bactericidal titers suggest that <10% of children <4 years old retained a >/=4-fold increase at 7 months following vaccination. Of particular note, 59 of 79 sera (75%) from the 1- and 2-year-olds had high ELISA antibody concentrations (2 to 20 microg/ml) with no associated bactericidal titer (<1:8). Discordant results between bactericidal titers and ELISA antibody concentrations were not explained by the presence of IgA blocking antibody or relative levels of IgG and IgM. The bactericidal results show age-dependent differences in the production and retention of antibody in young children immunized with serogroup C polysaccharide; these differences are not evident with the ELISA data.

Sequencing ofporAfrom clinical isolates ofNeisseria meningitidisdefines a subtyping scheme and its genetic regulation

Subtyping Neisseria meningitidis by methods that rely on monoclonal antibody (mAb) reactivity results in an unusually high number of strains that are not subtypeable. To subtype 48 strains isolated (1993-1994) in the province of Quebec that were not subtypeable by mAb-based techniques, we used DNA sequencing of the variable regions of porA, a gene that encodes the class 1 outer membrane protein. We assigned subtypes to all the previously nonserosubtypeable isolates and identified some novel subtypes. Because our sequencing strategy included the promoter region of porA, different isolates were compared in their sequences of the porA promoter region. A poly(G) stretch lies between the -10 and -35 regions of the promoter; replacement of a G residue by an A residue in this region resulted in loss of expression of porA. No correlation was found between the number of G residues in the poly(G) stretch and the level of expression; a minimum of 10 G residues is required in this stretch for expression of porA. One isolate expressed no class 1 outer membrane protein because of the insertion sequence IS1301 in the coding region of porA. Another isolate did not express the protein owing to a frame-shift mutation within the coding region of porA. Sequencing of porA allowed assignments of subtypes to previously uncharacterized isolates and provided insights about the regulation of expression of this gene in N. meningitidis.Key words: Neisseria meningitidis, outer membrane proteins, subtyping, PorA, DNA sequencing.

[Analysis of the management of the vaccination campaign in 1996-1997 against meningococcus C in Galicia]

This paper describes the process to design and plan a vaccination campaign against group C N. Meningitidis developed in the Autonomous Community of Galicia between December 9, 1996 and January 31, 1997. We also analyse the results of this process in terms of management results, vaccine coverage and preliminary estimates of effectiveness. A Work group was established, made up of professionals in charge of different intervention areas. A person was designated in charge of the whole campaign and a follow-up and information system was created. The work plan consisted of daily meetings for follow-up, co-ordination and task distribution; and periodical meetings with primary health care and peripheral public health coordinators. Strategies of implantation--in order to make sure the campaign accessibility and acceptability; of budget and of communication with health workers, inhabitants and mass media were developed. Up to 100 tasks were identified to develop the technical information and logistic activities: mailings, meetings, leaflets, ...; purchasing of 584.980 doses of vaccine, supplying to 715 vaccination points (1040 deliveries); problem solving and intervention recording. A vaccination coverage of 85% was achieved, with notification of 8 adverse reactions and 6 errors in the administration of the vaccine (34 children affected). The strategy chosen for the design and planning of the campaign has proven to be effective and valid and sufficient to achieve the final goals, in due time and without problems of misinformation, shortage of vaccine or lack of participation of professionals or people. Mistakes due to incorrect administration of the vaccine, management problems, rupture of the cold chain or recording failures were minimal and accidental.

[Immunologic behavior of meningococcal vaccines]

Meningococcal disease continues to be a great health problem on all continents and the meningococcal vaccines have been proposed for their prevention and epidemic control. The polysaccharide A and C vaccines are relatively efficacious with distinct immunological behavior with regard to the different age groups, however, up to the present no highly efficacious vaccine for meningococcal B disease exists. The meningococcal B capsular polysaccharide is not immunogenic due to the structural mimicry of mammalian tissues and efforts to produce carrier proteins have been proposed in order to obtain an immunogenic vaccine for all age groups that would if possible, protect against all the meningococci. This review of the literature presents the study of the development of the immunological behavior of all the meningococcal vaccines undergoing development and reports on the efforts to obtain a safe and efficacious product for the control of meningococcal disease.

Standardization and a multilaboratory comparison of Neisseria meningitidis serogroup A and C serum bactericidal assays. The Multilaboratory Study Group

A standardized serum bactericidal assay (SBA) is required to evaluate the functional activity of antibody produced in response to Neisseria meningitidis serogroup A and C vaccines. We evaluated assay parameters (assay buffer, target strains, growth of target cells, target cell number, complement source and concentration, and methods for growth of surviving bacteria) which may affect the reproducibility of SBA titers. The various assay parameters and specificity of anticapsular antibody to five serogroup A strains (A1, ATCC 13077, F8238, F9205, and F7485) and four serogroup C strains (C11, G7880, G8050, and 1002-90) were evaluated with Centers for Disease Control and Prevention meningococcal quality control sera. The critical assay parameters for the reproducible measurement of SBA titers were found to include the target strain, assay incubation time, and complement. The resulting standardized SBA was used by 10 laboratories to measure functional anticapsular antibody against serogroup A strains F8238 and serogroup C strain C11. In the multilaboratory study, SBA titers were measured in duplicate for 14 pairs of sera (seven adults and seven children) before and after immunization with a quadrivalent polysaccharide (A, C, Y, and W-135) vaccine. The standardized SBA was reliable in all laboratories regardless of experience in performing SBAs. For most sera, intralaboratory reproducibility was +/- 1 dilution; interlaboratory reproducibility was +/- 2 dilutions. The correlation between median titers (interlaboratory) and enzyme-linked immunosorbent assay total antibody concentrations was high for both serogroup A (r = 0.86; P < 0.001; slope = 0.5) and serogroup C (n = 0.86; P < 0.001; slope = 0.7). The specified assay, which includes the critical parameters of target strain, incubation time, and complement source, will facilitate interlaboratory comparisons of the functional antibody produced in response to current or developing serogroup A and C meningococcal vaccines.