India-made typhoid vaccine efficacy lasts for four years: study

India-made typhoid vaccine efficacy lasts for four years: study

Subject: Science and tech

Section: Health

Context:

• A phase-3 trial conducted in Malawi on children aged between nine months and 12 years has demonstrated that the “Typbar” typhoid vaccine, developed by Hyderabad-based Bharat Biotech, maintains its efficacy for at least four years.

Details:

• The trial, which is the first randomised, controlled, double-blind study of its kind in a typhoid fever-endemic setting.
• The vaccine’s efficacy ranges from 70.6% to over 79%.
• The study provides evidence of the vaccine’s long-term protection beyond 48 months, with minimal decline in efficacy over time, supporting its cost-effectiveness.
• It also notes the robust immune response induced by conjugated typhoid vaccines in individuals older than six months, mentioning two WHO-prequalified vaccines: Bharat Biotech’s Typbar TCV and Biological E’s Vi-CRM197.
• However, concerns about the potential rebound of Salmonella Typhi bacteria in vaccinated children due to waning protection suggest the need for further research on the vaccine’s long-term efficacy and the possible benefits of a booster dose, with an immunogenicity study of a booster dose currently underway in Malawi.

Typbar- Typhoid vaccine:

• Typbar TCV® is the world’s first clinically proven conjugate typhoid vaccine, notable for containing the polysaccharide of Salmonella typhi Ty2 conjugated to Tetanus Toxoid.
• This conjugation method enhances the immune response by eliciting T-dependent antibody responses, characterized by the production of high-affinity antibodies and the establishment of long-term immune memory, beyond the basic B cell responses elicited by the Vi capsular polysaccharide alone.
• Significantly, Typbar TCV® is the only typhoid vaccine approved for use in children and infants under 2 years of age.
• It has received WHO prequalification, underscoring its global importance in typhoid fever prevention.

About Typhoid fever:

• It is a serious infection caused by Salmonella Typhi, a bacterium transmitted exclusively through humans.
• It spreads via the fecal-oral route, commonly through contaminated food or water. Without treatment, 1 in 20 recovered individuals becomes a symptomless carrier, capable of infecting others for up to a year.
• Typhoid fever is prevalent in parts of Asia, Africa, the Caribbean, Central and South America, and the Middle East, posing a risk, especially to travellers.
• Symptoms of typhoid can range from mild to severe, including fever, fatigue, malaise, sore throat, persistent cough, and headache, lasting about a month without treatment.
• Prevention is possible through vaccination, available as a live, attenuated capsule for individuals over 6 years or an inactivated shot for those over 2 years, administered two weeks before travel. However, the vaccine’s effectiveness ranges from 50–80%.
• Treatment necessitates prompt antibiotic administration. The emergence of drug-resistant strains, however, threatens the efficacy of these treatments.
• Multi-drug-resistant (MDR) typhoid, which shows resistance to multiple antibiotic classes, has been a concern but has declined in Bangladesh and India since 2000, remained low in Nepal, and slightly increased in Pakistan.
• A newer threat is Extensive Drug Resistance (XDR) typhoid, resistant to at least five classes of antibiotics, observed in India, Bangladesh, Nepal, and Pakistan, posing a significant public health risk.

Source: TH