Evidence of Extended Thermo-Stability of Typhoid Polysaccharide Conjugate Vaccines.

Fang Gao,Sarah Davis,Kay Lockyer,Samuel Pradeep Dondapati,Barbara Bolgiano,Sjoerd Rijpkema,Gopal Singh,Sai D Prasad,Alastair Logan,Gurbaksh Singh Sounkhla

doi:10.3390/microorganisms9081707

Fang Gao, Sarah Davis + Show 8 more

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https://doi.org/10.3390/microorganisms9081707

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Abstract

Typhoid conjugate vaccines (TCV) are effective in preventing enteric fever caused by Salmonella enterica serovar Typhi in Southeast Asia and Africa. To facilitate vaccination with the Vi capsular polysaccharide–tetanus toxoid conjugate vaccine, Typbar TCV, and allow it to be transported and stored outside a cold chain just prior to administration, an extended controlled-temperature conditions (ECTC) study was performed to confirm the quality of the vaccine at 40 °C for 3 days at the end of its shelf-life (36 months at 2–8 °C). Studies performed in parallel by the vaccine manufacturer, Bharat Biotech International Limited, and an independent national control laboratory (NIBSC) monitored its stability-indicating parameters: O-acetylation of the Vi polysaccharide, integrity of the polysaccharide–protein conjugate, and its molecular size and pH. ECTC samples stored at 40 °C and 45 °C in comparison with control samples stored at 4 °C and 55 or 56 °C, were shown to have stable O-acetylation and pH; only very slight increases in the percentage of free saccharide and corresponding decreases in molecular size were observed. The deoxycholate method for precipitating conjugated polysaccharide was very sensitive to small incremental increases in percentage of free saccharide, in line with storage temperature and duration. This extended ECTC study demonstrated minimal structural changes to the Vi polysaccharide and conjugate vaccine and a stable formulation following extended exposure to elevated temperatures for the desired durations. This outcome supports the manufacturer’s ECTC claim for the vaccine to be allowed to be taken outside the cold chain before its administration.

Highlights

Of thermostable vaccines to control enteric fever in endemic regions of Asia and Africa would benefit country health programs, international organizations and vaccine producers
Enteric fever is caused by systemic infection with Salmonella enterica subspecies serovars Typhi
Whilst non-typeable Salmonella infections typically cause diarrheal illness, typhoid infections typically produce bacteremia accompanied by febrile illnesses, with prolonged high fever and headache being common symptoms [3]. These infections are relatively common in low- and middle-income countries (LMICs) with poor water supply and sanitation, but infections can be controlled through vaccination with typhoid conjugate vaccines

Summary

Introduction

Of thermostable vaccines to control enteric fever in endemic regions of Asia and Africa would benefit country health programs, international organizations and vaccine producers. Enteric fever is caused by systemic infection with Salmonella enterica subspecies serovars Typhi Typhi in 2019 and 14.3 million from both S. Typhi in 2017, contributing to approximately 1.53 million deaths per annum [1,2]. Whilst non-typeable Salmonella infections typically cause diarrheal illness, typhoid infections typically produce bacteremia accompanied by febrile illnesses, with prolonged high fever and headache being common symptoms [3]. These infections are relatively common in low- and middle-income countries (LMICs) with poor water supply and sanitation, but infections can be controlled through vaccination with typhoid conjugate vaccines. Vaccination can break the escalating cycle of antibiotic resistance

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