New Delhi: A Bharat Biotech vaccine that prevents typhoid fever, caused by a drug-resistant bacteria and prevalent in Africa, has been found to be safe and effective for children under the age of 12 in Phase 3 clinical trials.
The typhoid fever, caused by H58 Salmonella Typhi, a type of bacteria that has become resistant to multiple drugs, is an increasing public health threat in sub-Saharan Africa.
A team of scientists, including researchers from University of Oxford, conducted a Phase 3, double-blind trial in Blantyre, Malawi, to assess the efficacy of Vi polysaccharide typhoid conjugate vaccine (Vi-TCV).
Developed by Bharat Biotech, the Vi-TCV or Typbar TCV — the world’s first clinically proven conjugate Typhoid vaccine — contains a carbohydrate from the Salmonella typhi Ty2 bacteria, along with the Tetanus vaccine.
While the Salmonella typhi carbohydrate alone elicits B cell responses, the inclusion of the tetanus vaccine elicits higher-affinity antibodies and long-term immune memory.
Such a vaccine is known as conjugate vaccines — where a weak antigen is combined with a strong antigen — so that the immune system has a stronger response. An antigen is a part of the pathogen that the body can identify.
The Typbar TCV is the world’s first clinically proven conjugate Typhoid vaccine.
India’s top virologist Dr Gagandeep Kang, who is also a professor at the Christian Medical College in Vellore, also tweeted on the development.
An Indian made typhoid vaccine ready to solve problems in Africa-great, long awaited data here. Gavi Alliance is supporting vaccine introductions in Asia and Africa.
Safety and Efficacy of a Typhoid Conjugate Vaccine in Malawian Children | NEJM https://t.co/hNKoDmHUBu
— G Kang (@GKangInd) September 18, 2021
The Phase 3 trials
In the latest clinical trial, the results of which have been published in the journal NEJM, researchers randomly assigned 28,130 children who were between 9 months and 12 years of age to either receive a single dose of Vi-TCV or meningococcal capsular group A conjugate (MenA) vaccine.
Blood culture tests confirmed typhoid fever occurred in 12 children among the 14,069 children in the Vi-TCV group and in 62 children in the MenA group of 14,061 children.
Among Malawian children, administration of Vi-TCV resulted in a lower incidence of blood culture, confirmed typhoid fever, than the MenA vaccine. The vaccine was found to provide a protective efficacy of 80.7 per cent.
The efficacy of Vi-TCV was similar in children who were younger than five years of age and children who were five years of age or older at the time of vaccination, and this efficacy remained consistent throughout the observation period.
In total, 130 serious adverse events occurred in the first 6 months after vaccination — 52 in the Vi-TCV group and 78 in the MenA group — including 6 deaths (all in the MenA group). No serious adverse events were considered by the investigators to be related to vaccination.
In their papers, researchers noted that efficacy of Vi-TCV after 18 to 24 months was consistent with a previously reported efficacy of 81.6 per cent after 12 months of follow-up among Nepalese children of 9 months to 16 years of age.
The team said that despite a 2008 WHO recommendation for programmatic use of existing vaccines in countries in which typhoid is endemic, no African country integrated these vaccines into routine schedules, largely because of the unsuitability of their use in the youngest children and the need for repeated doses.
Malawi, where the trial was conducted, has a high prevalence of typhoid among school-age and preschool children.
Based on their findings, the team now recommends a routine introduction of Vi-TCV among infants, coupled with catch-up campaigns targeting children up to the age of 15 years to control drug-resistant typhoid.
(Edited by Arun Prashanth)
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