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10 MAY 2016
A new study by icddr,b scientists and published in the New England Journal of Medicine has shown for the first time that a single dose of the oral cholera vaccine Shanchol is effective in older children and adults in an area where cholera is endemic.
These findings will be eagerly received globally by health agencies interested in using the vaccine in a single dose in endemic areas where cholera is common, as well as in epidemic situations where disruption of healthcare infrastructure makes it difficult to complete the currently recommended two-dose regimen.
Child being fed oral cholera vaccine in Bangladesh. Photo: Graham Judd / icddr,b
The icddr,b study, done in collaboration with the Government of Bangladesh and the International Vaccine Institute in Seoul, and funded by the Bill and Melinda Gates Foundation, was conducted in the urban slums of Mirpur, an area of Dhaka, Bangladesh with high rates of cholera.
The researchers randomised non-pregnant residents over the age of 1 year to a single dose of oral cholera vaccine (Shanchol) or placebo.
The vaccine was 40% protective against all cholera episodes up to 6 months after dosing and 63% protective against severely dehydrating cholera.
Overall, 204,700 received one complete dose of vaccine or placebo and among these 101 first cholera episodes were detected during the six months of follow-up, 37 with severe dehydration.
The vaccine was safe and adverse event rates were similar in the vaccine and placebo groups.
Dr Firdausi Qadri, a Scientist in the Infectious Diseases Division at icddr,b, who led the study, says that “a single dose of the oral cholera vaccine was safe and provided protection against cholera for at least 6 months of follow-up.” The vaccine was particularly effective at preventing cholera with severe dehydration.
“However, the single dose vaccine was not protective for young children under the age of 5 years although 2 doses of the vaccine has been shown to be effective in this age group,” she noted.
“Our results are very encouraging and show that a single dose of the OCV is effective in preventing disease in older children and adults in a highly cholera endemic setting in the world,” she added.
At the same time, because the findings show that even a single dose provides at least short-term protection of older children and adults, the vaccine is still likely to be beneficial during epidemics occurring in the wake of humanitarian disasters: “Infrastructural challenges to completing a two-dose regimen should not deter the use of the vaccine to help contain epidemics in these settings,” says Professor John D Clemens, Executive Director of icddr,b and senior author on the paper.
Previously, the two-dose regimen of Shanchol, a World Health Organization pre-qualified oral cholera vaccine, was found in a trial in Kolkata to confer 65% protection that was sustained for at least 5 years. More recently, when delivered through routine government services in Dhaka, the same regimen was found by icddr,b scientists to confer 53% protection over two years of follow-up, as recently published in The Lancet.
The full findings of the single-dose study were published in the New England Journal of Medicine.