One-shot vaccine offers typhoid hope
[NEW DELHI] A cheap single-shot vaccine can protect young children from typhoid, new research shows.
The vaccine, originally developed by Indian company Biological E in 1999, costs as little as 50 US cents per dose.
It can protect 80 per cent of children aged less than five years, according to the study, which was conducted in a Kolkata slum where the disease is prevalent.
The WHO recommends two anti-typhoid vaccines. One is an oral vaccine, Ty21a, a capsule that must be taken three times. The second is an injectable vaccine that can be given as a single shot.
But despite WHO recommendations, the injection has not been widely used in public-health programmes in developing countries because of doubts over its effectiveness.
In addition, "many developing countries lack sufficient surveillance infrastructure to document burden, and are therefore unaware of the magnitude of the problem or even the specific highest-risk age groups", Abdullah Brooks, head of the infectious diseases unit at the International Centre for Diarrhoeal Disease Research in Bangladesh, told SciDev.Net. "Thus, there is no demand from the public or policymakers."
Typhoid is a deadly bacterial infection, endemic in the developing world, that is spread through contaminated water and food. Caused by the bacterium Salmonella enterica Typhi, it causes up to 600,000 deaths per year. In most countries, infections peak in school-age children, but in the urban slums of South Asia they tend to peak in pre-school children.
The study, conducted by the National Institute of Cholera and Enteric Diseases (NICED) in Kolkata and the International Vaccine Institute in Seoul, was carried out on more than 37,000 children aged between two and 18 years. The initial study was done in 2004, and subjects were followed up for two years.
The protection rate of 80 per cent in children under five years old falls to 56 per cent in children aged 5-14, and 46 per cent in older children.
An additional benefit is 'herd protection' — 44 per cent of unvaccinated people living close to vaccinated people were protected as the spread of infection stopped.
"This is important new information," said Myron Levine, director of the Center for Vaccine Development at the University of Maryland, in an accompanying commentary in the New England Journal of Medicine (NEJM). It "further bolsters the case for school-based immunisation to control endemic typhoid, since one might expect some indirect protection of pre-school children as well".
The study was published in the NEJM last week (23 July).
New Engl. J. Med. 361, 335 (2009)