Bangalore: The existing, inexpensive vaccine for typhoid in the country can protect 80% of preschool children and should be used for mass immunization, but countries such as India have failed to do this due to uncertainties about its effectiveness, says a new study in Thursday’s issue of the New England Journal of Medicine.
Click here for an interview with Deepika Sur, chief researcher of the study on typhoid vaccines
More than two decades after typhoid vaccines—Ty21a and Vi polysaccharide—hit the market, India, owing to its lack of clean drinking water for all, continues to have typhoid outbreaks. According to the World Health Organization, or WHO, of around 500,000 typhoid deaths globally every year, 400,000 occur in Asia.
“We undertook this large study (on 37,673 children) on the slum dwellers of eastern Kolkata to show that logistically and programmatically it is possible to deliver low-cost Vi vaccine in diverse settings and that it is effective,” said Dipika Sur, principal investigator of the study from the National Institute of Cholera and Enteric Diseases in Kolkata. Unlike regular clinical trials, that test the efficacy of the drug, this study was for “effectiveness” in real-life situations, she said.
“With this study, we’ll try to convince the government to include it in the national programme...We have also done a cost effectiveness and a behavioural study (which is another publication),” Sur added.
The study was funded by the Bill and Melinda Gates Foundation. The Vi vaccines were donated by GlaxoSmithKline Pharmaceuticals Ltd, Indian arm of the European firm.
Ty21a is an oral vaccine and is given in three doses; Vi is a one-dose injectable vaccine. The former, though, is not readily available and can be given to children only over six years of age. A bonus from this study is the finding that the Vi vaccine also protected unvaccinated children from typhoid in the control group living in the neighbourhood as bacteria transmission was blocked by the vaccinated group.
Experts say this indirect protection bolsters the argument for school-based immunization. “Even if the protection is for three years, it is good enough,” said John D. Clemens, co-author of the study at the International Vaccine Institute in Seoul, South Korea.
“The public health importance of typhoid is under-ascertained and the governments don’t have a good handle on the typhoid burden,” said Clemens. “Unlike dengue fever, which is dramatic in nature and gets publicized, typhoid doesn’t get on the radar of governments and the media.”
The paediatric community in the country has been advocating mass immunization of children. The vaccine is readily available from multinational firms such as GSK and Aventis Pasteur Inc. as well as Indian generic drug makers including Bharat Biotech International Ltd and Panacea Biotec Ltd.
The Indian Academy of Pediatrics has been recommending typhoid as well as rota virus and pneumococcal vaccines for long, said Dinesh Kaul, consultant paediatrician at Sir Ganga Ram Hospital in New Delhi.
Theoretically, “conjugate” vaccines—a new class of vaccines with better immunity—can solve some of the logistical issues as it can be clubbed with other routine vaccines given to children below two years of age.
“Conjugate vaccines hold promise but there’s been only one trial in Vietnam, which showed 90% protection for many years and we are still a few years away from it,” said Clemens. “Vi polysaccharide vaccine is far from perfect but will significantly bring down the disease burden,” he added.