Antibody Persistence at 1 and 4 Years Following a Single Dose of MenAfriVac or Quadrivalent Polysaccharide Vaccine in Healthy Subjects Aged 2-29 Years

Zika Virus in West Africa: A Seroepidemiological Study between 2007 and 2012

According to the World Health Organization, the entire African continent is at risk of a Zika outbreak. To increase data availability on the epidemiology of Zika virus circulation in Africa, we evaluated the immunity to Zika virus in a selected cohort of subjects from West Africa between 2007 and 2012. Human serum samples were collected in 2007 and in 2011/2012 from a cohort of 2-29-year-old subjects from Mali, Senegal, and The Gambia. A sample that tested positive by Zika virus IgG ELISA and by Zika virus microneutralization test was defined as positive. In 2007, the highest prevalence was 21.9%, found in Senegal among 18-29-year-old subjects. In 2011/2012, the highest prevalence, 22.7%, was found still in Senegal, but in 11-17-year-old subjects. During both study periods, the lowest prevalence was found in Mali, where few positive cases were found only in 18-29-year-old subjects. The Gambia showed an intermediate prevalence. In the three countries, prevalence was strongly associated with increasing age. This study contributes to understanding Zika virus circulation within three different ecological and demographic contexts with scarce or no data currently available. Results showed that Zika virus circulated actively in West Africa between the period 2007 and 2011/2012, but with some geographic specificity.

Serogroup A meningococcal conjugate vaccines: building sustainable and equitable vaccine strategies

INTRODUCTION

For well over 100 years, meningococcal disease due to serogroup A Neisseria meningitidis (MenA) has caused severe epidemics globally, especially in the meningitis belt of sub-Saharan Africa.

AREAS COVERED

The article reviews the background and identification of MenA, the global and molecular epidemiology of MenA, and the outbreaks of MenA in the African meningitis belt. The implementation (2010) of an equitable MenA polysaccharide-protein conjugate vaccine (PsA-TT, MenAfriVac) and the strategy to control MenA in sub-Saharan Africa is described. The development of a novel multi-serogroup meningococcal conjugate vaccine (NmCV-5) that includes serogroup A is highlighted. The PubMed database (1996-2019) was searched for studies relating to MenA outbreaks, vaccine, and immunization strategies; and the Neisseria PubMLST database of 1755 MenA isolates (1915-2019) was reviewed.

EXPERT OPINION

Using strategies from the successful MenAfriVac campaign, expanded collaborative partnerships were built to develop a novel, low-cost multivalent component meningococcal vaccine that includes MenA. This vaccine promises greater sustainability and is directed toward global control of meningococcal disease in the African meningitidis belt and beyond. The new WHO global roadmap addresses the continuing problem of bacterial meningitis, including meningococcal vaccine prevention, and provides a framework for further reducing the devastation of MenA.

Antibody Persistence at the Population Level 5 Years After Mass Vaccination With Meningococcal Serogroup A Conjugate Vaccine (PsA-TT) in Burkina Faso: Need for a Booster Campaign?

Background

In Burkina Faso, serogroup A meningococcal (NmA) conjugate vaccine (PsA-TT, MenAfriVac) was introduced through a mass campaign in children and adults in December 2010. Similar to a serological survey in 2011, we followed population-level antibody persistence for 5 years after the campaign and estimated time of return to previously-published pre-vaccination levels.

Methods

We conducted 2 cross-sectional surveys in 2013 and early 2016, including representative samples (N = 600) of the general population of Bobo-Dioulasso, Burkina Faso. Serum bactericidal antibody titers (rabbit complement) were measured against NmA reference strain F8236 (SBA-ref), NmA strain 3125 (SBA-3125), and NmA-specific immunoglobulin G (IgG) concentrations.

Results

During the 2016 survey, in different age groups between 6 and 29 years, the relative changes in geometric means compared to 2011 values were greater among younger age groups. They were between -87% and -43% for SBA-ref; -99% and -78% for SBA-3125; and -89% and -63% for IgG. In linear extrapolation of age-specific geometric means from 2013 to 2016, among children aged 1-4 years at the time of the PsA-TT campaign, a return to pre-vaccination levels should be expected after 12, 8, and 6 years, respectively, according to SBA-ref, SBA-3125, and IgG. Among older individuals, complete return to baseline is expected at the earliest after 11 years (SBA-ref and SBA-3125) or 9 years (IgG).

Conclusions

Based on SBA-3125, a booster campaign after 8 years would be required to sustain direct immune protection for children aged 1-4 years during the PsA-TT campaign. Antibodies persisted longer in older age groups.

Antibody kinetics following vaccination with MenAfriVac: an analysis of serological data from randomised trials

BACKGROUND

A meningococcal group A conjugate vaccine, PsA-TT (also known as MenAfriVac), was developed with the support of the Meningitis Vaccine Project. Around 280 million individuals aged 1-29 years have been immunised across the African meningitis belt. We analysed the kinetics of vaccine-induced antibody response and assessed the possible implications for duration of protection.

METHODS

We obtained data from two longitudinal studies done in The Gambia, Mali, and Senegal of antibody responses in 193 children aged 12-23 months and 604 participants aged 2-29 years following MenAfriVac vaccination. Antibodies were measured using two methods: group A serum bactericidal antibody (SBA) assay and group A-specific IgG ELISA. Data on antibody responses were analysed using a mixed-effects statistical model accounting for the mean response and variation in patterns of antibody kinetics. Determinants of antibody duration were investigated using regression analysis.

FINDINGS

In children age 12-23 months, the reduction in MenAfriVac-induced antibody levels assessed by SBA titres had two phases: with 97·0% (95% credible interval [CrI] 95·1-98·3) of the response being short lived and decaying within the first 6 months and the remainder being long lived and decaying with a half-life of 2690 days (95% CrI 1016-15 078). Antibody levels assessed by SBA titres in participants aged 2-29 years were more persistent, with 95·0% (85·7-98·1) of the response being short lived, and the long lived phase decaying with a half-life of 6007 days (95% CrI 2826-14 279). Greater pre-vaccination antibody levels were associated with greater immunogenicity following vaccination, as well as greater antibody persistence. Despite rapid antibody declines in the first phase, antibodies in the second phase persisted at SBA titres greater than 128. Although there is no strong evidence base for a correlate of protection against infection with Neisseria meningitidis serogroup A, we use an assumed SBA titre of 128 as a threshold of protection to predict that 20 years after vaccination with a single dose of MenAfriVac, vaccine efficacy will be 52% (29-73) in children vaccinated at age 12-23 months and 70% (60-79) in participants vaccinated at age 2-29 years.

INTERPRETATION

Population-level immunity induced by routine vaccination with the Expanded Programme on Immunization is predicted to persist at levels sufficient to confer more than 50% protection over a 20-year time period. Further increases in population-level immunity could be obtained via mass campaigns or by delaying the age of vaccination through the Expanded Programme on Immunization. However, the benefits of such a strategy would need to be weighed against the risks of leaving young children unvaccinated for longer.

FUNDING

Meningitis Vaccine Project and Institut Pasteur.

Initial validation of a simulation model for estimating the impact of serogroup A Neisseria meningitidis vaccination in the African meningitis belt

We previously developed a mathematical simulation of serogroup A Neisseria meningitidis (NmA) transmission in Burkina Faso, with the goal of forecasting the relative benefit of different vaccination programs. Here, we revisit key structural assumptions of the model by comparing how accurately the different assumptions reproduce observed NmA trends following vaccine introduction. A priori, we updated several of the model's parameters based on recently published studies. We simulated NmA disease under different assumptions about duration of vaccine-induced protection (including the possibility that vaccine-induced protection may last longer than natural immunity). We compared simulated and observed case counts from 2011-2017. We then used the best-fit model to forecast the impact of different vaccination strategies. Our updated model, with the assumption that vaccine-induced immunity lasts longer than immunity following NmA colonization, was able to reproduce observed trends in NmA disease. The updated model predicts that, following a mass campaign among persons 1-29 years of age, either routine immunization of 9 month-old children or periodic mini-campaigns among children 1-4 years of age will lead to sustained control of epidemic NmA in Burkina Faso. This validated model can help public health officials set policies for meningococcal vaccination in Africa.

Proceedings of the first African Health Forum: effective partnerships and intersectoral collaborations are critical for attainment of Universal Health Coverage in Africa

BACKGROUND

Universal Health Coverage (UHC)is central to the health Sustainable Development Goals(SDG). Working towards UHC is a powerful mechanism for achieving the right to health and promoting human development which is a priority area of focus for the World Health Organization WHO. As a result, the WHO Regional Office for Africa convened the first-ever Africa Health Forum, co- hosted by the government of Rwanda in Kigali in June 2017 with the theme "Putting People First: The Road to Universal Health Coverage in Africa". The Forum aimed to strengthen and forge new partnerships, align priorities and galvanize commitment to advance the health agenda in Africa in order to attain UHC and the SDGs. This paper reports the proceedings and conclusions of the forum.

METHODS

The forum was attended by over 800 participants. It employed moderated panel and public discussions, and side events with political leaders, policy makers and technicians from ministries of health and finance, United Nations agencies, the private sector, the academia, philanthropic foundations, youth, women and non-governmental organizations drawn from within and outside the Region.

CONCLUSIONS

The commitment to achieve UHC was a collective expression of the belief that all people should have access to the health services they need without risk of financial hardship. The attainment of UHC will require a significant paradigm shift, including development of new partnerships especially public-private partnerships in selected areas with limited government resources, intersectoral collaboration to engage in interventions that affect health but are outside the purview of the ministries in charge of health and identification of public health issues where knowledge gaps exist as research priorities. The deliberations of the Forum culminated into a "Call-to-Action" - Putting People First: The Road to Universal Health Coverage in Africa, which pledged a renewed determination for Member States, in partnership with the private Sector, WHO, other UN Agencies and partners to support the attainment of the SDGs and UHC. There was agreement that immediate action was required to implement the call-to-action, and that the African Regional Office of WHO should develop a plan to rapidly operationalize the outcomes of the meeting.

Clinical data supporting a 2-dose schedule of MenB-FHbp, a bivalent meningococcal serogroup B vaccine, in adolescents and young adults

Invasive meningococcal disease (IMD) caused by Neisseria meningitidis is a potentially devastating condition that can result in death and is associated with serious long-term sequelae in survivors. Vaccination is the preferred preventative strategy. Quadrivalent polysaccharide-based vaccines that protect against infection caused by meningococcal serogroups A, C, W, and Y are not effective against meningococcal serogroup B (MenB), which was responsible for approximately 60% and 35% of confirmed IMD cases in the European Union and the United States in 2016, respectively. A recombinant protein MenB vaccine (MenB-FHbp [bivalent rLP2086; Trumenba®]) has been approved for protection against MenB infection in persons 10-25 years of age in the United States and Canada and for individuals ≥10 years of age in the European Union and Australia. In these regions, MenB-FHbp is approved as a 2- or 3-dose primary vaccination schedule. This report will review the current evidence supporting administration of MenB-FHbp as a 2-dose primary vaccination schedule. Different contexts in which a 2- or 3-dose primary vaccination schedule might be preferred (eg, routine prospective vaccination vs outbreak control) are reviewed.

Community Perspectives Associated With the African PsA-TT (MenAfriVac) Vaccine Trials

Background. The Meningitis Vaccine Project (MVP) was established to address epidemic meningitis as a public health problem in sub-Saharan Africa and, to that end, worked to develop a group A meningococcal conjugate vaccine, PsA-TT.

Methods. Experiences in 4 clinical trial sites are described. Culturally sensitive collaborative strategies were adopted to manage acceptable communication methods, peculiarities with the consent process, participant medical issues, community care, and death.

Results. The clinical trials were completed successfully through community acceptance and active community collaboration. The trials also strengthened the capacities in the participating communities, and actively worked to resolve community problems.

Conclusions. The understanding and integration of sociocultural realities of communities were major assets in the conduct and acceptance of these trials. MVP succeeded in these sites and provided a sound example for future clinical studies in Africa.

Clinical Trials Registration. ISRTCN78147026 (PsA-TT 002); ISRCTN87739946 (PsA-TT 003); ISRCTN82484612 (PsA-TT 004); PACTR ATMR2010030001913177 (PsA-TT 006); and PACTR201110000328305 (PsA-TT 007).

Antibody Persistence 1-5 Years Following Vaccination With MenAfriVac in African Children Vaccinated at 12-23 Months of Age

Background. Following mass vaccination campaigns in the African meningitis belt with group A meningococcal conjugate vaccine, MenAfriVac (PsA-TT), disease due to group A meningococci has nearly disappeared. Antibody persistence in healthy African toddlers was investigated.

Methods. African children vaccinated at 12–23 months of age with PsA-TT were followed for evaluation of antibody persistence up to 5 years after primary vaccination. Antibody persistence was evaluated by measuring group A serum bactericidal antibody (SBA) with rabbit complement and by a group A–specific IgG enzyme-linked immunosorbent assay (ELISA).

Results. Group A antibodies measured by SBA and ELISA were shown to decline in the year following vaccination and plateaued at levels significantly above baseline for up to 5 years following primary vaccination.

Conclusions. A single dose of PsA-TT induces long-term sustained levels of group A meningococcal antibodies for up to 5 years after vaccination.

Clinical Trials Registration. ISRTCN78147026.

Meningococcal quadrivalent tetanus toxoid conjugate vaccine (MenACWY-TT, Nimenrix™): A review of its immunogenicity, safety, co-administration, and antibody persistence

INTRODUCTION

Meningococcal disease is a major cause of morbidity and mortality worldwide with reported epidemics and outbreaks in different parts of the world. Despite the availability of antimicrobial therapy, challenges remain in early recognition and prevention of disease. Several vaccines have been developed to date aiming at preventing disease spread.

DISCUSSION

MenACWY-TT (Nimenrix™) has been extensively studied for use in different age groups. Phase II and III randomized trials have demonstrated its immunogenicity when administered in children aged 1 year and older, adolescents and adults. It has an acceptable safety profile with minor adverse events comparable to other vaccines. Follow up studies have shown persistence of protective antibodies up to three years. MenACWY-TT was safely and effectively co-administered with different recommended vaccines.

CONCLUSION

MenACWY-TT is a safe and immunogenic vaccine that can be used to protect against these four serogroups in individuals older than 1 year of age.