Typhoid vaccines. Historical aspects of typhoid vaccine development, and currently available products

Typhoid fever is an acute infectious disease caused by Salmonella enterica subsp. enterica serovar Typhi (S. Typhi), which is still extremely common in endemic low- and middle-income countries of Asia and Africa. Industrialised countries may also be affected by typhoid fever outbreaks due to booming international tourism, and natural disasters. Given S. Typhi progressive resistance to antibiotics, high epidemiological burden, and lack of adequate sanitation and hygiene in a number of regions, the introduction of new treatment protocols and the improvement of preventive vaccination are critical tasks in global healthcare. The aim of the study was to highlight the main historical aspects of the typhoid vaccine development, to summarise data on the licensed vaccines and promising approaches to the development of new typhoid vaccines. The paper describes the current epidemiological situation of typhoid fever globally and in the Russian Federation. It dwells upon the global experience in typhoid vaccine development from the production of an inactivated vaccine to the development of conjugated vaccines. The paper summarises data on Russian and foreign-made typhoid fever vaccines currently available in the global pharmaceutical market. It outlines the main trends in the development of vaccines against the disease caused by S. Typhi. The paper demonstrates the need for improving the efficacy of existing vaccines and development of new typhoid combination vaccines.

Typhoid and paratyphoid fever: a clinical seminar

Rationale for review: Enteric fever (EF) caused by Salmonella enterica subspecies enterica serovar Typhi (Salmonella Typhi) and S. Paratyphi (Salmonella Paratyphi) remains an important cause of infectious morbidity and mortality in many low-income countries and, therefore, still poses a major infectious risk for travellers to endemic countries. Main findings: Although the global burden of EF has decreased over the past two decades, prevalence of EF remains high in Asia and Africa, with the highest prevalence reported from the Indian subcontinent. These statistics are mirrored by data on travel-related EF. Widespread and increasing antimicrobial resistance has narrowed treatment options for travel-related EF. Ceftriaxone- and azithromycin-based therapies are commonly used, even with the emergence of extremely drug-resistant typhoid in Pakistan. Preventive measures among locals and travellers include provision of safe food and water and vaccination. Food and water precautions offer limited protection, and the efficacy of Salmonella Typhi vaccines is only moderate signifying the need for travellers to be extra cautious. Recommendations: Improvement in the diagnosis of typhoid with high degree of clinical suspicion, better diagnostic assays, early and accurate detection of resistance, therapy with appropriate drugs, improvements in hygiene and sanitation with provision of safe drinking water in endemic areas and vaccination among travellers as well as in the endemic population are keys to controlling typhoid. While typhoid vaccines are recommended for travellers to high-risk areas, moderate efficacy and inability to protect against Salmonella Paratyphi are limitations to bear in mind. Improved Salmonella Typhi vaccines and vaccines against Salmonella Paratyphi A are required.

Travelers’ vaccines and their adverse events in Nara, Japan

Background: It is important to analyze the types of vaccines in travel clinics to determine the focus points in future practice. Methods We retrospectively reviewed the electronic medical records of all patients who visited the travel clinic of Nara Medical University between June 2013 and December 2019 to determine their background and the vaccines administered. The information regarding adverse events of the unapproved vaccines in Japan (Havrix®, Verorab®, Boostrix®, Priorix®, Typhim Vi®, and Mencevax®) was also collected. Results Of 645 patients, 58.6% were men and the median age was 31 years. Business was the most common travel purpose (34.9%), and Southeast Asia was the most common destination (40.2%). More than 80% of travelers to low- and middle-income countries were vaccinated against hepatitis A, while the rabies vaccination rate was approximately 50%. Typhoid vaccination coverage among travelers to South Asia was approximately 50%. The incidence of adverse events requiring medical consultation, telephonic consultation, or prolonged stay in the examination room was less than 5% for all unapproved vaccines in Japan. Conclusion More patient education is needed to increase the vaccination rate of rabies and typhoid vaccines. Adverse events to unapproved vaccines in Japan were not high and were well-tolerated.

Review on the Recent Advances on Typhoid Vaccine Development and Challenges Ahead

Control of Salmonella enterica serovar typhi (S. typhi), the agent of typhoid fever, continues to be a challenge in many low- and middle-income countries. The major transmission route of S. typhi is fecal-oral, through contaminated food and water; thus, the ultimate measures for typhoid fever prevention and control include the provision of safe water, improved sanitation, and hygiene. Considering the increasing evidence of the global burden of typhoid, particularly among young children, and the long-term horizon for sustained, effective water and sanitation improvements in low-income settings, a growing consensus is to emphasize preventive vaccination. This review provides an overview of the licensed typhoid vaccines and vaccine candidates under development, and the challenges ahead for introduction.

Adverse Events Following Immunization With Combined vs Concurrent Monovalent Hepatitis A and Typhoid Vaccines in Children

Combined hepatitis A and typhoid vaccine is available in Australia, but licensed for use from age 16 years; however it is used “off-label” in children. The combined vaccine is well tolerated in children aged 2–16 years and the risk of adverse events is similar to those receiving concurrent monovalent vaccines.

Why Is Eradicating Typhoid Fever So Challenging: Implications for Vaccine and Therapeutic Design

Salmonella enterica serovar Typhi (S. Typhi) and S. Paratyphi, namely typhoidal Salmonellae, are the cause of (para) typhoid fever, which is a devastating systemic infectious disease in humans. In addition, the spread of multidrug-resistant (MDR) and extensively drug-resistant (XDR) S. Typhi in many low and middle-income countries poses a significant risk to human health. While currently available typhoid vaccines and therapeutics are efficacious, they have some limitations. One important limitation is the lack of controlling individuals who chronically carry S. Typhi. However, due to the strict host specificity of S. Typhi to humans, S. Typhi research is hampered. As a result, our understanding of S. Typhi pathogenesis is incomplete, thereby delaying the development and improvement of prevention and treatment strategies. Nonetheless, to better combat and contain S. Typhi, it is vital to develop a vaccine and therapy for controlling both acutely and chronically infected individuals. This review discusses how scientists are trying to combat typhoid fever, why it is so challenging to do so, which approaches show promise, and what we know about the pathogenesis of S. Typhi chronic infection.