TCV: A breakthrough for preventing typhoid

The news on the pre-qualification of Typhoid Conjugate Vaccine (TCV) by the World Health Organisation (WHO) on January 3, 2018 and endowment by Gavi, the Vaccine Alliance have dawned a unique beginning for the entire field of public health. For the first time, a vaccine has been prequalified by WHO that is only needed in the routine immunisation programmes of low- and middle-income countries in the South Asia and Africa.

Prof Dr Samir Saha, Head of Department of Microbiology, Dhaka Shishu Hospital and Executive Director of Child Health Research Foundation (CHRF) and his team has been working on Meningitis and Pneumonia for the last several decades to generate evidence and facilitate the introduction of vaccines against Haemophilus influenzae type b (Hib) and Streptococcus pneumoniae — two devastating organisms that affect children under 5 years of age in developing countries.

When both vaccines were introduced in Bangladesh, they were proud but not satisfied. Much to their surprise, during all their surveillance studies, typhoid always emerged as the largest fraction of all invasive bacterial diseases, in spite of the fact that they were not even looking for it. Typhoid, then, was so neglected that it did not even make it to WHO's list of neglected diseases.

Historically, three countries of the South Asia — Bangladesh, India, and Pakistan — were assumed to bear the largest burden of typhoid.

There are a few ways of treating and preventing typhoid: through use of effective antibiotics, through improvement of water supply, sanitation, and hygiene (WaSH) systems and through vaccines.

With rising antimicrobial resistance, antibiotics are becoming less effective; improvements in WaSH worked well in developed countries but comes with an exorbitant price tag in any low- and middle-income nations.

The decision of WHO for recommending the introduction of TCV in typhoid-endemic countries was a very pleasant surprise for all of us living in the developing world with high prevalence of typhoid.

Dr Samir and his team did not expect anyone to invest on typhoid as it is the 'disease of the poor' and the associated possibility of market failure. On an average, they observed that 3 out of 4 blood cultures isolates in the community was Salmonella typhi, the causative organism of typhoid, and yet it went disregarded as a high burden infectious disease.

Vaccination is not the end of the story either. It requires continuous surveillance to measure the impact of TCV introduction on typhoid burden and the improvement of the overall health system. It will be vital to keep a close monitor the behaviour of the distant cousin of Salmonella typhi, Salmonella paratyphi, during the post TCV period.

Dr Samir urges that industries should not decelerate their effort on development of a bivalent vaccine that can prevent diseases by both these pathogens. Bangladeshis, like any other low-key and middle-income countries, usually receive a vaccine after 20-25 years of its introduction in the developed world — pneumococcal vaccines took 20 years and Hib vaccine took 25 years to travel in Bangladesh. This is the first time that a vaccine will be first introduced in a country where it is needed the most. Its introduction will be a huge public health triumph.