A Japanese study to assess immunogenicity and safety of a typhoid Vi polysaccharide vaccine

Evaluation of Vaccine Safety After the First Public Sector Introduction of Typhoid Conjugate Vaccine-Navi Mumbai, India, 2018

BACKGROUND

In December 2017, the World Health Organization (WHO) prequalified the first typhoid conjugate vaccine (TCV; Typbar-TCV). While no safety concerns were identified in pre- and postlicensure studies, WHO's Global Advisory Committee on Vaccine Safety recommended robust safety evaluation with large-scale TCV introductions. During July-August 2018, the Navi Mumbai Municipal Corporation (NMMC) launched the world's first public sector TCV introduction. Per administrative reports, 113 420 children 9 months-14 years old received TCV.

METHODS

We evaluated adverse events following immunization (AEFIs) using passive and active surveillance via (1) reports from the passive NMMC AEFI surveillance system, (2) telephone interviews with 5% of caregivers of vaccine recipients 48 hours and 7 days postvaccination, and (3) chart abstraction for adverse events of special interest (AESIs) among patients admitted to 5 hospitals using the Brighton Collaboration criteria followed by ascertainment of vaccination status.

RESULTS

We identified 222/113 420 (0.2%) vaccine recipients with AEFIs through the NMMC AEFI surveillance system: 211 (0.19%) experienced minor AEFIs, 2 (0.002%) severe, and 9 serious (0.008%). At 48 hours postvaccination, 1852/5605 (33%) caregivers reported ≥1 AEFI, including injection site pain (n = 1452, 26%), swelling (n = 419, 7.5%), and fever (n = 416, 7.4%). Of the 4728 interviews completed at 7 days postvaccination, the most reported AEFIs included fever (n = 200, 4%), pain (n = 52, 1%), and headache (n = 42, 1%). Among 525 hospitalized children diagnosed with an AESI, 60 were vaccinated; no AESIs were causally associated with TCV.

CONCLUSIONS

No unexpected safety signals were identified with TCV introduction. This provides further reassurance for the large-scale use of Typbar-TCV among children 9 months-14 years old.

Vaccine development for enteric bacterial pathogens: Where do we stand?

Gut infections triggered by pathogenic bacteria lead to most frequently occurring diarrhea in humans accounting for million deaths annually. Currently, only a few licensed vaccines are available against these pathogens for mostly travelers moving to diarrheal endemic areas. Besides commercialized vaccines, there are many formulations that are either under clinical or pre-clinical stages of development and despite several efforts to improve safety, immunogenicity and efficacy, none of them can confer long-term protective immunity, for which repeated booster doses are always recommended. Further in many countries, financial, social and political constraints have jeopardized vaccine development program against these pathogens that enforce us to gather knowledge on safety, tolerability, immunogenicity and protective efficacy regarding the same. In this review, we analyze safety and efficacy issues of vaccines against five major gut bacteria causing enteric infections. The article also simultaneously describes several barriers for vaccine development and further discusses possible strategies to enhance immunogenicity and efficacy.

S. typhi Vi capsular polysaccharide vaccine-induced humoral immunity in travellers with immunosuppressive therapy for rheumatoid disease

INTRODUCTION

Typhoid fever is a global health problem, causing significant morbidity and mortality. Currently, the most widely used vaccine is the typhoid Vi capsular polysaccharide (Vi-PS) vaccine. While epidemiological studies on its efficacy have been performed in children in endemic countries, there are no efficacy studies evaluating its use in travel medicine. Response to vaccination may differ in travellers receiving immunosuppressive therapy. This study investigates the humoral response to Vi-PS vaccination in travellers receiving immunosuppressive therapy for rheumatoid disease.

METHODS

We recruited patients from the LUMC rheumatology outpatient clinic and travellers from the travel clinic who had previously received Vi-PS vaccination and also immunosuppressive therapy for rheumatoid disease. We analysed blood samples acquired from 42 patients over a period of 3 years. We estimated the length of persistence of protective titres using the survival analysis using multiple cut-off values for protection and measured titre half-life and the influence of immunosuppressive medication on titre half-life using mixed models.

RESULTS

Anti-Vi-PS antibody levels stayed above 10 EU/ml for a mean of 13.3 years, above 15 EU/ml for a mean of 10.1 years and above 20 EU/ml for a mean of 8.6 years after Vi-PS vaccination. Titre half-life was 7.5 years (95% CI 5.0-14.7 years, P < 0.001). No significant influence of medication on titre half-life was found.

CONCLUSION

Both persistence of protective antibody titres and titre half-life are longer than expected based on other studies. This warrants further study in adult volunteers, both in healthy individuals and patients suffering from rheumatoid disease.

Measurement and interpretation of Salmonella typhi Vi IgG antibodies for the assessment of adaptive immunity

Response to polysaccharide vaccination can be an invaluable tool for assessing functionality of the adaptive immune system. Measurement of antibodies raised in response to Pneumovax®23 is the current gold standard test, but there are significant challenges and constraints in both the measurement and interpretation of the response. An alternative polysaccharide vaccine approach (Salmonella typhi Vi capsule (ViCPS)) has been suggested. In the present article, we review current evidence for the measurement of ViCPS antibodies in the diagnosis of primary and secondary antibody deficiencies. In particular, we review emerging data suggesting their interpretation in combination with the response to Pneumovax®23 and comment upon the utility of these vaccines to assess humoral immune responses while receiving immunoglobulin replacement therapy (IGRT).

Typhoid Vaccination among Japanese Travelers to South Asia and the Factors Associated with Compliance

Objective In 2010, candid advice concerning the low rate of typhoid vaccination among Japanese travelers was received from Nepal. Recently, progressive Japanese travel clinics have encouraged Japanese travelers to be vaccinated against typhoid fever in conjunction with officially approved vaccines, such as hepatitis A vaccine. We herein report the status of typhoid vaccinations for Japanese travelers to the most endemic area (South Asia) and describe the factors associated with compliance. Methods In the travel clinic at Kurume University Hospital, we used the following criteria to retrospectively extract the records of new pre-travel Japanese clients between January 2011 and March 2015: hepatitis A vaccine administered, traveling to South Asian countries, and ≥2 years of age. We first summarized the participants and then divided them into typhoid-vaccinated and typhoid non-vaccinated groups for a comparative analysis. Results This study included 160 clients. A majority (70.0%) of these clients traveled for business. The duration of trips was long (≥1 month) (75.0%), and India was a popular destination (90.6%). A comparative study between the vaccinated group (n=122) and the non-vaccinated group (n=38) revealed that the two factors most positively associated with typhoid vaccination were business trips [adjusted odds ratio (aOR) 3.59, 95% confidence interval (CI) 1.42-9.06] and coverage by a company/organization payment plan (aOR 7.14, 95% CI 2.67-20.3). Conclusion The trend toward typhoid vaccination among Japanese travelers to South Asia with pre-travel consultation is correlated with business trips and coverage by a company/organization payment plan. If problems concerning the cost of vaccines were resolved, more travelers would request typhoid vaccination.