In a new study published in New England Journal of Medicine (NEJM) on May 5, 2016, researchers have reported that single dose of oral killed cholera vaccine, which was given in two dose regiment before, provides 40% protection against the disease for at least six months in a population living in endemic area.
Firdausi Qadri, PhD, of International Centre for Diarrheal Disease Research, Bangladesh (ICDDR, B) and co-authors wrote that the vaccine can also provide 63% protective efficacy against severely dehydrating cholera.
Another observation indicated that the vaccine did not provide protection to children under the age of five. As the authors report it, the probable reason for it can be the “not yet developed” additional resistance to cholera, which is usually present in highly endemic areas.
The older children and adults according to the study did develop sufficient short term protection with a single dose of the killed oral cholera vaccine. The researchers assume that this finding will help ‘to not worry about the challenges of operating two dose cholera vaccination programs’ when developing strategies for endemic control.
The study was carried out in urban slums of Mirpur in Dhaka, Bangladesh, where endemic of cholera reaches peak in the months of March and April. The study period was from January 2014 to February 2014, where participants were given a single dose of vaccine or a placebo. The results were published on observations made during the initial six months of vaccination.
In the randomized placebo-controlled study to measure efficacy, initially 352, 157 patients were assessed, 205,513 underwent randomized vaccination, and 204, 700 of those were considered to be included in final analysis of the data after accounting for migration and deaths. All participants were more than one year of age and were not pregnant.
Primary outcome was set as a culture confirmed cholera case occurring between seven and 180 days of vaccination. Secondary outcome was considered to be the proportion of severe dehydrating disease cases over the same period.
There were 101 first cholera episodes, including 37 severe dehydration cases, which followed the same pattern of case load and calendar timing observed previously in the region. All cases observed of cholera after vaccinations were V. cholerae O1 El Tor biotype.
The total cases reported had 63 in placebo group and 38 in the vaccine group, with respective rates of 0.62 and 0.37 per 1,000 in their categories. All these cases projected a protective efficacy of 40%.
The 37 severe cases with 27 in placebo and 10 in the vaccine group had a protective efficacy of 63%.
Groups of participants one to four, five to fourteen, and fifteen to older, showed respective efficacies of 16%, 63%, and 56%.
Efficacy, not to be confused with effectiveness, of a vaccine represents the percentage of reduction of disease in a group which was vaccinated compared to a group which was not vaccinated, in a controlled setting. Effectiveness represents how well the vaccine works when they are used in routine conditions in a community.
The authors made two important notes. First, the vaccine’s performance in an uncontrolled setting can be different, especially where cholera does not exist as an endemic (no natural immunity in residents of the area). Second, these results represent only short term protection.
The vaccine used in the study named Shanchol, is a licensed drug of Shantah Biotechnics of India. The vaccine, a killed whole-cell-only oral drug comes in vials containing 1.5 ml of liquid agent. One dose of the vaccine costs 1.85 US dollars.
Initial trials for the vaccine have shown five-year conferred cumulative protection of the vaccine with two doses at 65% and two-year cumulative protection at 53%.
World Health Organization (WHO) on the basis of these statistics started collecting a stockpile of the vaccine, for possible future epidemics arising after natural disaster like the one in Haiti in 2010. That particular outbreak killed more than 7,000 people and diseased a population of 600,000.
The important question which remained, after these studies, was whether a second dose of vaccine was needed when the first dose was providing “substantial immunologic responses” in epidemic areas. According to authors, studies like the one published by NEJM, can answer such questions and help policymakers make informed financial, and economic decisions when managing an epidemic.
Cholera, often caused by a potentially fatal bacterial strain and transmitted through water or food, currently causes 28,000 to 142,000 deaths worldwide annually. 80% of the infections can be controlled with the administration of oral rehydration pills but if left untreated can kill a patient within hours.