Oral cholera vaccine interventions show promising success

Delivery of the second dose of the two-dose oral cholera vaccines (OCV) through a self-administration strategy deployed by icddr,b researchers has proven successful in vaccinating an urban Dhaka slum population, shown in a recent study.

OCVs provide 3-5 years of protection against cholera. Photo: Rabiul Hasan / icddr,b

Around 93 percent of recipients of the first dose of the two dose regimen were found to have taken the second dose themselves when these were given out to them in a zip-lock bag for consumption two weeks after the initial dose.

“OCV in studies carried out by us earlier has shown that it is stable for up to six weeks at ambient temperatures,” says Dr Firdausi Qadri, icddr,b senior scientist and senior author of the study published in Vaccine.

The empty vials of the second dose of OCV were collected later by visiting houses to ensure that the vaccine vials were taken by the participants. About 98 percent recipients appreciated this strategy, she adds.

Urban slum population are one of the most vulnerable to cholera. Photo: Shumon Ahmed / icddr,b

Two of the major challenges of delivering vaccines to communities are cold chain maintenance in order to preserve the vaccines, and organising human resource for administering vaccine delivery. Dr Qadri and colleagues have already shown that OCVs are stable in elevated temperature without cold chain which enabled carrying out large scale field trials to administer OCVs without refrigeration.

“Successful implementation of this self-administration delivery strategy can be an alternative solution for delivering vaccines to hard-to-reach populations, in resource-poor settings or during a humanitarian crisis, when households are able to properly store and use an OCV product as instructed,” says Dr Ashraful Islam Khan, icddr,b associated scientist and first author of the recently published important study.


Harnessing an unrestrainable foe: Cholera

Cholera continues to be a public health challenge in Bangladesh, especially in endemic areas such as slums that face a huge deficiency of clean water, hygiene and sanitation (WASH) facilities. OCVs provide modest efficacy and 3-5 years of protection against cholera. They have been used in large scale campaigns over the last five years to curb epidemics, and also in endemic areas where WASH conditions are still lacking and inadequate.

WASH conditions are poor in the Rohingya camps in Cox's Bazaar. Photo: Rabiul Hasan / icddr,b

The studies at icddr,b have shown that even a single dose regimen of inactivated whole-cell OCV can  provide protection for up to two years to older children (over 5 years)  and adults, according to icddr,b findings in the Lancet Infectious Diseases.

Studies have shown that oral cholera vaccines have a significant impact on reducing cholera in populations, by both direct and indirect, herd protection effects, that is even among those not vaccinated as shown by an icddr,b study looking at the effects of mass cholera vaccination.


“This is known as the herd immunity,” says Prof John Clemens MD, icddr,b executive director and a senior author of the study published in PLOS NTD.

“Immunising a significant proportion of a population makes it difficult for an infectious diseases like cholera to spread to non-vaccinees, since the herd effects of OCVs interrupt transmission” clarifies Prof Clemens.

Although the herd effects of immunisation is found useful, organising human resources for vaccine delivery, especially in remote and formidable settings, is yet another challenge that icddr,b researchers have examined which has been carried out in Dhaka city as well as in rural settings and during humanitarian crises among the forcibly displaced Myanmar nationals in Rohingya camps in Cox’s Bazar.

Prof John Clemens (2L), Dr Qadri (2R) and Dr Ashraf (3R) visit the Rohingya camps. Photo: icddr,b

Not very far from urban Bangladesh is Keraniganj, a rural setting with modestly-equipped public health facilities. The OCV team at icddr,b explored whether it is feasible and cost-effective to undertake a mass vaccination campaign in this area using the existing government vaccine delivery system.

“The first OCV dose could cover almost 90 percent of the targeted population, and of them 92% were covered for the second dose,” notes Dr Qadri, senior author of this study published in Human Vaccines & Immunotherapeutics.

Dr Qadri believes that these findings, demonstrating an acceptable delivery cost, confirms the success of using existing government system to deliver OCVs.


Way Forward

One of the most recent and successful examples of averting cholera was the pre-emptive emergency OCV deployment for the Forcibly Displaced Myanmar Nationals (FDMNs) in Rohingya camps in Bangladesh.

icddr,b researchers visit during vaccination at the Rohingya camp. Photo: Rabiul Hasan / icddr,b

Many of these people including children were unvaccinated with the EPI vaccines and had been forced to a setting under conditions with a heightened likelihood of cholera epidemics due to the existing compromised WASH conditions.

“Our OCV campaign in collaboration with the Bangladesh Government and international partners provides a model for pre-emptive delivery of OCVs from the WHO stockpile to avert major cholera epidemics in complex humanitarian emergencies,” observes Prof Clemens in a commentary published in The Lancet.

The icddr,b studies earlier and especially those carried out recently provide evidence of successful interventions to tackle  two major challenges – cold chain management and appropriate human resources. The icddr,b OCV team anticipate that people prone to cholera in Bangladesh can be protected with locally produced OCVs which will become available in the near future, as noted by the researchers in a recent commentary in The Journal of Infectious Diseases.