Impact of meningococcal vaccination with combined serogroups A and C polysaccharide vaccine on carriage of Neisseria meningitidis C

Longitudinal study of meningococcal carriage in adolescents and young adults in South Australia 2017-2020

BACKGROUND

This analysis investigated longitudinal changes in meningococcal carriage in adolescents in South Australia over 4 years.

METHODS

Data from the "B Part of It" study, which included a state-wide cluster randomized controlled trial in secondary-school students (n = 34,489 in 2017 and 2018) and serial cross-sectional studies in school leavers aged 17-25 years (n = 4028 in 2019-2020). Individuals had oropharyngeal swabs collected annually. This study included two unique cohorts: (1) individuals enrolled in 2019, with three consecutive annual swabs taken in 2017, 2018 and 2019; and (2) individuals enrolled in 2020, with swabs taken in 2017, 2018, and 2020. Disease-associated N. meningitidis genogroups were identified using PCR and whole genome sequencing. Univariate analysis identified risk factors for recurrent carriage (≥2).

RESULTS

Among school leavers, 50 (1.7%, total n = 2980) had carriage detected at successive visits. In participants with meningococcal carriage at successive visits, 38/50 (76.0%) had the same genogroup detected by porA PCR. Of those, 19 had the same MLST type and demonstrated minimal variation, indicating they most likely had sustained carriage of the same isolate (range 226 to 490 days, mean duration 352 [SD 51] days). In the 2019 school leaver cohort, 6.7% acquired carriage in their first year out of school compared to 3.3% in their final school year. Compared to single carriage detection, recurrent carriage was potentially more likely in older adolescents (16 compared to ≤15 years; OR = 1.97 (95%CI 1.0, 3.86); p = 0.048).

CONCLUSION

Whilst carriage is typically transient, some adolescents/young adults may have persistent carriage and are likely to be an important group in the transmission of meningococci.

Epidemiology and prevention of meningococcal disease: a critical appraisal of vaccine policies

Meningococcal disease is characterized by a marked variation in incidence and serogroup distribution by region and over time. In several European countries, Canada and Australia, immunization programs, including universal vaccination of infants or toddlers with catch-up campaigns in children and adolescents, aimed at controlling disease caused by meningococcal serogroup C have been successful in reducing disease incidence through direct and indirect protection. More recently, meningococcal conjugate vaccines targeting disease caused by serogroups A, C, W-135 and Y have been licensed and are being used in adolescent programs in the USA and Canada while a mass immunization campaign against serogroup A disease has been implemented in Africa. Positive results from clinical trials using vaccines against serogroup B disease in various age groups suggest the possibility of providing broader protection against serogroup B disease than is provided by the currently used outer membrane vesicle vaccines. The purpose of our review of meningococcal epidemiology and assessment of existing policies is to set the stage for future policy decisions. Vaccination policies to prevent meningococcal disease in different regions of the world should be based on quality information from enhanced surveillance systems.

Systematic review: Impact of meningococcal vaccination on pharyngeal carriage of meningococci

OBJECTIVE

To investigate the effect of meningococcal vaccines on pharyngeal carriage of meningococci.

METHODS

Systematic review. MEDLINE and EMBASE were searched for relevant studies. Controlled trials and observational studies which used comparison groups or compared carriage rates before and after vaccination were included in the review.

RESULTS

Twenty-nine studies satisfied the inclusion criteria. Twenty-five studies reported the effect of a polysaccharide vaccine, one the effect of a serogroup C conjugate vaccine and three the impact of serogroup B outer-membrane vaccines on overall and/or serogroup-specific meningococcal carriage rates. Ten studies of meningococcal polysaccharide vaccines found reduced serogroup-specific carriage; seven of these focussed on high-risk groups and had a short follow-up period. Only one of five studies of civilian populations in Africa showed a significantly reduced carriage. Many studies had methodological shortcomings. The one study which assessed the effect of a meningococcal conjugate vaccine on carriage showed a significant impact. Three studies of serogroup B outer-membrane protein vaccines showed no effect on carriage.

CONCLUSIONS

A few well-designed trials of the impact of meningococcal vaccines on carriage have been undertaken. Such studies should be an essential component of the evaluation of new meningococcal vaccines, particularly those introduced to control epidemic meningococcal disease in Africa.

Development of immunity to serogroup B meningococci during carriage of Neisseria meningitidis in a cohort of university students

Understanding the basis of protective immunity is a key requirement for the development of an effective vaccine against infection with Neisseria meningitidis of serogroup B. We have conducted a longitudinal study into the dynamics of meningococcal acquisition and carriage in first-year university students. The detection of carriage of serogroup B meningococci correlated with an increase in detection of serum bactericidal activity (SBA) against both colonizing and heterologous serogroup B strains. Once induced, SBA remained high throughout the study. Although students showed increases in antibodies reactive with capsular polysaccharide and lipopolysaccharide (LPS), these antibody responses were transitory, and their decline was not accompanied by a corresponding decline in SBA. In contrast, there was a significant correlation between the presence of antibodies to the PorA outer membrane protein and SBA against both homologous and heterologous strains. SBA induced by a PorA-negative mutant confirmed the contribution of PorA to heterologous activity. Increases in SBA against a range of serogroup B strains were also observed in students in whom no meningococcal carriage was detected. This heterologous protection could not be associated with the presence of antibodies reacting with capsule, LPS, PorA, PorB, Rmp, Opa, Opc, or pilin, demonstrating that other, as yet unidentified, antigens contribute to the development of immunity to serogroup B meningococci. Identification of such antigens with the ability to induce an effective cross-reactive bactericidal response to a range of strains would be a major step in the production of a universally effective vaccine against infections caused by serogroup B meningococci.

Neisseria meningitidis: an overview of the carriage state

During periods of endemic disease, about 10 % of the general population harbour Neisseria meningitidis in the nasopharynx. Since N. meningitidis is a strict human pathogen and most patients have not been in contact with other cases, asymptomatic carriers are presumably the major source of the pathogenic strains. Most carrier isolates are shown to lack capsule production. The capsule deficient state of meningococcal strains in the nasopharynx may aid evasion of the human immune defence and hence be selected to survive nasopharyngeal colonization. Carriage itself can be an immunizing process resulting in systemic protective antibody responses. Frequent nasopharyngeal colonization with related bacteria like Neisseria lactamica improves natural immunity to meningococci by the formation of cross-reacting antibodies. While most meningococcal strains recovered from patients belong to a limited number of clonal groups worldwide, strains isolated from carriers comprise numerous genotypes, with only a small proportion of the strains representing invasive clones. During the carriage state, co-colonization with other pathogenic and non-pathogenic bacteria may lead to genetic exchange, which may result in the emergence of new meningococcal clones. The high diversity of meningococcal carrier strains, compared with hypervirulent strains, supports the idea that transmissibility, not invasion, is essential in the life cycle of N. meningitidis.

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.