A typhoid vaccine (Typbar TCV) developed by the Hyderabad-based Bharat Biotech has shown 81.6% efficacy in preventing typhoid fever at 12 months in a Phase-III clinical trial. The trial was carried out in Nepal in over 10,000 children who received the vaccine.
A single does of the vaccine was found to be effective in preventing typhoid in children aged nine months to 16 years. The vaccine confers protection two-three weeks after vaccination. The duration of protection is currently not known. The results of the trial were published in The New England Journal of Medicine (NEJM).
The Typbar TCV vaccine was recommended by WHO’s Strategic Advisory Group of Experts on Immunization (WHO-SAGE) in December 2017. WHO prequalified the vaccine in January 2018.
Typhoid fever is caused by the highly contagious Salmonella Typhi bacteria. Nearly 11 million fall sick due to typhoid and about 1,17,000 deaths are reported each year. The bacteria spread through contaminated food or water.
The Typbar TCV typhoid vaccine tested in Nepal is a conjugate vaccine. Conjugate vaccine is one in which the antigen (which is a polysaccharide in this case) is chemically linked to a carrier protein.
Two other typhoid vaccines — polysaccharide typhoid vaccine and live, weakened typhoid vaccine — are already used commercially. But the efficacy of the vaccines to protect against typhoid is lower than the conjugate vaccine that was tested in Nepal.
“The other two vaccines offer 60-70% protection unlike the conjugate vaccine which confers nearly 82% protection. Two doses of live, weakened typhoid vaccine are needed to reach 60-70% protection,” says Dr. V. Krishna Mohan, Executive Director at Bharat Biotech.
“More importantly, the conjugate vaccine can be given to babies as young as six months, while the other two vaccines cannot be given to children below two years of age.”
According to SAGE, in high-incidence settings, a large proportion of severe typhoid fever cases occur in children aged below two years.
While typhoid bacteria can be treated with antibiotics, the microbes have developed resistance against multiple antibiotics. Multi-drug resistant typhoid bacteria are seen in south Asia including India. Since 2016, extensively drug-resistant (XDR) typhoid outbreaks have been reported from Sindh province in Pakistan. According to an Editorial accompanying the paper, XDR typhoid has been found in India, Bangladesh, and Pakistan.
“Right now in Pakistan, a strain of typhoid has developed resistance to all but one of the antibiotics we use to treat the disease, threatening to take us back to the days when typhoid killed as many as one-fifth of the people that contracted it,” Dr. Seth Berkley, chief executive of Gavi, the Vaccine Alliance, told BBC.
Bharat Biotech has been supplying the typhoid conjugate vaccine to Pakistan since 2017. “So far about 10 million vaccines have been supplied to Pakistan,” says Dr. Mohan. Pakistan is the first country to introduce the typhoid conjugate vaccine as part of its national immunisation programme.