Vaccines for the prevention of meningococcal disease in children

Enhanced immune response of T-cell independent or dependent antigens in SIGN-R1 knock-out mice

Dextran was used to explore a novel method of enhancing an immune response against T-cell independent type 2 (TI-2) polysaccharide antigens, because of its suitability as a model for the immunogenecity of many TI-2 polysaccharide antigens and its high affinity to SIGN-R1. Here we showed that the primary immune response of IgM, IgG3, and IgG2b was enhanced by dextran in SIGN-R1 knock-out (KO) mice, further evoking the induction of a secondary immune response to IgG2b in parallel. On the other hand, an immune response of IgG1 and IgG2b against T-cell dependent (TD) antigen was strongly enhanced by the administration of ovalbumin (OVA) in SIGN-R1 KO mice. These results indicate that SIGN-R1 is critical in the regulation of immune responses. Therefore, our study suggests that inhibition of TI-2 polysaccharide antigen uptake in SIGN-R1(+) macrophages contributes to the development of novel vaccination strategies against TI-2 polysaccharide antigens.

Baseline meningococcal carriage in Burkina Faso before the introduction of a meningococcal serogroup A conjugate vaccine

The serogroup A meningococcal conjugate vaccine MenAfriVac has the potential to confer herd immunity by reducing carriage prevalence of epidemic strains. To better understand this phenomenon, we initiated a meningococcal carriage study to determine the baseline carriage rate and serogroup distribution before vaccine introduction in the 1- to 29-year old population in Burkina Faso, the group chosen for the first introduction of the vaccine. A multiple cross-sectional carriage study was conducted in one urban and two rural districts in Burkina Faso in 2009. Every 3 months, oropharyngeal samples were collected from >5,000 randomly selected individuals within a 4-week period. Isolation and identification of the meningococci from 20,326 samples were performed by national laboratories in Burkina Faso. Confirmation and further strain characterization, including genogrouping, multilocus sequence typing, and porA-fetA sequencing, were performed in Norway. The overall carriage prevalence for meningococci was 3.98%; the highest prevalence was among the 15- to 19-year-olds for males and among the 10- to 14-year-olds for females. Serogroup Y dominated (2.28%), followed by serogroups X (0.44%), A (0.39%), and W135 (0.34%). Carriage prevalence was the highest in the rural districts and in the dry season, but serogroup distribution also varied by district. A total of 29 sequence types (STs) and 51 porA-fetA combinations were identified. The dominant clone was serogroup Y, ST-4375, P1.5-1,2-2/F5-8, belonging to the ST-23 complex (47%). All serogroup A isolates were ST-2859 of the ST-5 complex with P1.20,9/F3-1. This study forms a solid basis for evaluating the impact of MenAfriVac introduction on serogroup A carriage.

Henoch-Schölein purpura and polysaccharide meningococcal vaccine

BACKGROUND

We describe here a case of Henoch-Schönlein purpura (HSP) that occurred 10 days after administration of the meningococcal polysaccharide vaccine and came to the attention of a Vaccine Safety Datalink (VSD) investigator (but did not occur in the VSD cohort). Periodic case reports have linked vaccines to HSP.

OBJECTIVE

To better understand the potential risk for HSP after immunization with the meningococcal polysaccharide vaccine.

PATIENTS AND METHODS

We studied the VSD cohort to estimate the 42-day postvaccination incidence rate of HSP in the VSD population 16 to 20 years of age. Electronic data from all 8 VSD sites were gathered. All subjects aged 16 to 20 years who received a meningococcal polysaccharide vaccine were followed for 42 days after that vaccination for evidence of HSP. Background rates were determined by examining all the nonexposed time of the same cohort.

RESULTS

No cases of HSP were seen in the 42 days after 49,027 doses of meningococcal polysaccharide vaccine among the entire VSD adolescent and young adult population. The background incidence rate was 4.2 per 100,000 person-years.

CONCLUSION

These data provide the strongest evidence so far that HSP is not associated with receipt of meningococcal polysaccharide vaccine in the 16- to 20-year age group.

Reducing child mortality in Nigeria: a case study of immunization and systemic factors

The purpose of the study is to assess the outcome of the Expanded Program on Immunization (EPI) in Nigeria, as well as to examine systemic factors influencing its high under-five mortality rate (UFMR). The principal objective of the EPI program when it was implemented in 1978 was to reduce mortality, morbidity and disability associated with six vaccine preventable diseases namely tuberculosis, tetanus, diphtheria, measles, pertussis and poliomyelitis. The methodological approach to this study is quantitative, using secondary time series data from 1970 to 2003. The study tested three hypotheses using time series multiple regression analysis with autocorrelation adjustment as a statistical model. The results showed that the EPI program had little effect on UFMR in Nigeria. Only the literacy rate and domestic spending on healthcare had statistically significant effects on the UFMR. The military government was not a significant factor in reducing or increasing the UFMR. It appears that Nigeria needs a unified approach to healthcare delivery, rather than fragmented programs, to overcome cultural and political divisions in society.

Bacterial Meningitis in Burkina Faso: Surveillance Using Field-Based Polymerase Chain Reaction Testing

BACKGROUND

In addition to frequent epidemics of group A meningococcal disease, endemic bacterial meningitis due mostly to Neisseria meningitidis, pneumococcus, and Haemophilus influenzae type b is a serious problem in sub-Saharan Africa. The improved ability to identify the etiologic agent in cases of bacterial meningitis will facilitate more rapid administration of precise therapy.

METHODS

To describe the epidemiology of bacterial meningitis and evaluate the usefulness of field-based polymerase chain reaction (PCR) testing, we implemented population-based meningitis surveillance in Burkina Faso during 2002-2003 by use of PCR, culture, and antigen detection tests.

RESULTS

Among persons aged 1 month to 67 years, the incidences of meningococcal meningitis, pneumococcal meningitis, and Haemophilus influenzae type b meningitis were 19 cases (n=179), 17 cases (n=162), and 7.1 cases (n=68) per 100,000 persons per year, respectively. Of the cases of meningococcal meningitis, 72% were due to N. meningitidis serogroup W135. Pneumococcal meningitis caused 61% of deaths and occurred in a seasonal pattern that was similar to that of meningococcal meningitis. Of cases of pneumococcal meningitis and N. meningitidis serogroup W135 meningitis, 71% occurred among persons >2 years of age. Most patients, regardless of the etiology of their illness and the existence of an epidemic, received short-course therapy with oily chloramphenicol. Compared with culture as the gold standard, the sensitivity and specificity of PCR in the field were high; this result was confirmed in Burkina Faso and Paris.

CONCLUSIONS

Precise and rapid identification of etiologic agents is critical for improvement in the treatment and prevention of meningitis, and, thus, PCR should be considered for wider use in Africa. Vaccines against Streptococcus pneumoniae, N. meningitidis (including serogroup W135), and H. influenzae type b all will have a major impact on the bacterial meningitis burden. Antibiotic recommendations need to consider the importance of S. pneumoniae, even during the epidemic season.

Acute Bacterial Meningitis in Children

Despite advances in recent decades in management, including new and effective antimicrobials, children with bacterial meningitis still incur significant morbidity and mortality. Pathophysiologic processes including colonization and migration of the bacteria to blood, seeding of the meninges, and meningeal and brain inflammation have been largely elucidated, but more specific knowledge could lead to new effective therapies. Outside of the neonatal period, the most common causative organisms have been Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis. However, conjugate vaccines, especially the H influenzae type b preparation, have contributed significantly to steep declines in the incidence of meningitis. Optimal management consists of rapid diagnosis and administration of bactericidal antibiotics with properties allowing adequate penetration of the inflamed blood-brain barrier. Recently, development of microbial resistance has resulted in changes to recommended empiric antibiotic regimens. Novel therapies are under investigation; however, until controlled trials can be conducted, these therapies cannot be recommended.

Rates of Neisseria meningitidis increasing in young adults

The burden of meningococcal disease has remained unchanged in the United States for the past 4 decades. The currently available meningococcal vaccine is safe and effective, however, due to immunogenic limitations inherent to polysaccharide vaccines, it has been available only for high-risk populations older than 2. Incorporation of a more immunogenic and effective conjugated vaccine into the routine immunization schedule offers an opportunity to substantially affect the incidence of meningococcal disease. The routine use of a meningococcal conjugate vaccine in the United States will save lives and prevent significant morbidity in children and young adults.

Mucosal vaccination against serogroup B meningococci: induction of bactericidal antibodies and cellular immunity following intranasal immunization with NadA of Neisseria meningitidis and mutants of Escherichia coli heat-labile enterotoxin

Conjugated polysaccharide vaccines protect against serogroup C meningococci. However, this approach cannot be applied to serogroup B, which is still a major cause of meningitis. We evaluated the immunogenicity of three surface-exposed proteins from serogroup B Neisseria meningitidis (App, NhhA, and NadA) identified during whole-genome sequencing. Mice were immunized intranasally with individual proteins in the presence of wild-type Escherichia coli heat-labile enterotoxin (LTwt), LTR72, a partially inactivated mutant, or LTK63, a completely nontoxic mutant, as the adjuvant. Each of the meningococcal proteins induced significant cellular responses; NhhA and NadA induced strong antibody responses, but only NadA induced bactericidal antibody when administered intranasally with mucosal adjuvants. In addition, immunoglobulin A and bactericidal antibodies were detected in the respiratory tract following intranasal delivery of NadA. Analysis of antigen-specific cytokine production by T cells from immunized mice revealed that intranasal immunization with NadA alone failed to generate detectable cellular immune responses. In contrast, LTK63, LTR72, and LTwt significantly augmented NadA-specific gamma interferon, interleukin-4 (IL-4), IL-5, and IL-10 production by spleen and lymph node cells, suggesting that both Th1 and Th2 cells were induced in vivo. The strongest cellular responses and highest bactericidal antibody titers were generated with LTR72 as the adjuvant. These findings demonstrate that the quality and magnitude of the immune responses generated by mucosal vaccines are influenced by the antigen as well as the adjuvant and suggest that nasal delivery of NadA with mucosal adjuvants has considerable potential in the development of a mucosal vaccine against serogroup B meningococci.