Could a Shigella vaccine impact long-term health outcomes?: Summary report of an expert meeting to inform a Shigella vaccine public health value proposition, March 24 and 29, 2021

Epidemiology of Reportable Bacterial Infectious Diseases in Saudi Arabia

INTRODUCTION

Bacterial infections have a significant impact on human health; they can cause severe morbidity and mortality, particularly in susceptible populations. Epidemiological surveillance is a critical tool for monitoring the population's health and facilitate the prevention and control of infectious disease outbreaks. Knowing the burden of bacterial communicable diseases is an initial core step toward public health goals.

METHODS

Saudi epidemiology surveillance data were utilized to depict the changing epidemiology of bacterial infectious diseases in Saudi Arabia from 2018 to 2021. The cumulative numbers of cases, demographics, and incidence rates were analyzed and visualized. Parametric tests were used to compare the difference in the mean values between categorical variables. Regression analysis was employed to estimate trends in disease rates over time. Statistical significance was set at p value ≤ 0.05.

RESULTS

The results revealed that brucellosis, tuberculosis, and salmonellosis were the most frequently reported bacterial infectious diseases in Saudi Arabia. Males were more significantly affected by brucellosis and tuberculosis infections than females. Salmonellosis infections were more significant among Saudi citizens, while pulmonary tuberculosis was more significant in non-Saudis. Interestingly, there was a decline in the incidence rates of numerous bacterial infectious diseases during the Coronavirus Disease 2019 (COVID-19) pandemic and COVID-19 restrictions. Some bacterial infectious diseases were rarely reported in Saudi Arabia, including syphilis and diphtheria.

CONCLUSIONS

The future perspective of this research is to enhance disease surveillance reporting by including different variables, such as the source of infection, travel history, hospitalization, and mortality rates. The aim is to improve the sensitivity and specificity of surveillance data and focus on the mortality associated with bacterial pathogens to identify the most significant threats and set a public health priority.

Reassessing potential economic value and health impact of effective Shigella vaccines

The gram-negative bacterium Shigella is a leading cause of diarrheal morbidity and mortality in children in low- and middle-income countries. Several promising vaccine candidates are in late stages of clinical development against this increasingly antibiotic-resistant pathogen. However, considering the increasingly crowded and costly paediatric immunization schedule, and likely advent of other important new vaccines, it is unclear whether introduction of a Shigella vaccine would represent a high priority for international agencies or health ministries in low- and middle-income countries. To determine whether there is a compelling public health value proposition for a Shigella vaccine, we used the World Health Organization's Full Value of Vaccine Assessment analytic framework and formulated five broad scientific, policy, economic and commercial-related propositions regarding the development of a Shigella vaccine. We also explored the current regulatory, clinical, policy and commercial challenges to a Shigella-containing combination vaccine development and adoption. Through a series of literature reviews, expert consultations, social science field studies and model-based analyses, we addressed each of these propositions. As described in a series of separate publications that are synthesized here, we concluded that the economic and public health value of a Shigella vaccine may be greater than previously recognized, particularly if it is found to also be effective against less severe forms of diarrheal disease and childhood stunting. The decision by pharmaceutical companies to develop a standalone vaccine or a multipathogen combination will be a key factor in determining its relative prioritization by various stakeholders in low- and middle-income countries.

Exploring Shigella vaccine priorities and preferences: Results from a mixed-methods study in low- and middle-income settings

Background

Shigella is the leading bacterial cause of diarrheal mortality in children and can cause long-term effects on growth and development. No licensed Shigella vaccines currently exist but several promising candidates are in development and could be available in the next five years. Despite Shigella being a well-known public health target of the World Health Organization for decades, given current burden estimates and competing preventable disease priorities in low-income settings, whether the availability of an effective Shigella vaccine will lead to its prioritization and widespread introduction among countries at highest risk is unknown.

Methods

We conducted a mixed-methods study of national stakeholders and healthcare providers in five countries in Asia and Africa and regional stakeholders in the Pan American Health Organization to identify preferences and priorities for forthcoming Shigella vaccines.

Results

In our study of 89 individuals, diarrhea was the most frequently mentioned serious health concern for children under five years. Antimicrobial resistance (AMR) was more often considered very concerning than diarrhea or stunting. Shigella awareness was high but not considered a serious health concern by most stakeholders. Most participants were willing to consider adding a new vaccine to the routine immunization schedule but expressed reservations about a Shigella vaccine because of lower perceived burden relative to other preventable diseases and an already crowded schedule; interest was highest among national stakeholders in countries receiving more financial support for immunization. The priority of a Shigella vaccine rose when participants considered vaccine impacts on reducing stunting and AMR. Participants strongly preferred oral and combination vaccines compared to injectable and a single-antigen presentations, citing greater perceived community acceptability.

Conclusions

This study provides a critical opportunity to hear directly from country and regional stakeholders about health priorities and preferences around new vaccines. These findings should inform ongoing Shigella vaccine development efforts and eventual vaccine introduction and implementation planning.

Vaccine value profile for Shigella

Shigella is the leading bacterial cause of diarrhoea and the second leading cause of diarrhoeal mortality among all ages. It also exhibits increasing levels of antibiotic resistance. The greatest burden is among children under five in low- and middle-income countries (LMICs). As such, a priority strategic goal of the World Health Organization (WHO) is the development of a safe, effective and affordable vaccine to reduce morbidity and mortality from Shigella-attributable dysentery and diarrhea, including long term outcomes associated with chronic inflammation and growth faltering, in children under 5 years of age in LMICs. In addition, a safe and effective Shigella vaccine is of potential interest to travellers and military both to prevent acute disease and rarer, long-term sequelae. An effective Shigella vaccine is also anticipated to reduce antibiotic use and thereby help diminish further emergence of enteric pathogens resistant to antimicrobials. The most advanced vaccine candidates are multivalent, parenteral formulations in Phase 2 and Phase 3 clinical studies. They rely on O-antigen-polysaccharide protein conjugate technologies or, alternatively, outer membrane vesicles expressing penta-acylated lipopolysaccharide that has been detoxified. Other parenteral and oral formulations, many delivering a broader array of Shigella antigens, are at earlier stages of clinical development. These formulations are being assessed in alignment with the WHO Preferred Product Characteristics, which call for a 1 to 2 dose primary immunization series given during the first 12 months of life, ideally starting at 6 months of age. This 'Vaccine Value Profile' (VVP) for Shigella is intended to provide a high-level, holistic assessment of the information and data that are currently available to inform the potential public health, economic and societal value of pipeline vaccines and vaccine-like products. This VVP was developed by a working group of subject matter experts from academia, non-profit organizations, government agencies and multi-lateral organizations. All contributors have extensive expertise on various elements of the Shigella VVP and collectively aimed to identify current research and knowledge gaps. The VVP was developed using only existing and publicly available information.