Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. The Cochrane Infectious Diseases Group produces reviews that cover the prevention and treatment of a wide range of illnesses. These include cholera and their review on cholera vaccines was updated in January 2024. Here's the new lead author, KM Saif-Ur-Rahman from Evidence Synthesis Ireland and Cochrane Ireland in University of Galway to tell us more.

Saif: Cholera is a diarrheal disease, which spreads when people consume food or water containing the bacteria. It's prevalent in regions with inadequate sanitation and limited access to clean water, posing a heightened risk during humanitarian crises. Cholera can result in severe dehydration, and without prompt treatment, can be fatal.
Cholera vaccines have been in development for many years and oral vaccines are considered cost-effective and easy to administer. They can also be stored and delivered efficiently, even in humanitarian crises. Some oral cholera vaccines have received WHO pre-qualification, following a standardised evaluation and this is used by UN organizations like UNICEF for vaccine procurement.
In our updated Cochrane review, we have sought to quantify the efficacy and safety of WHO-prequalified oral inactivated cholera vaccines in preventing cholera among both children and adults. These are sometimes called "killed vaccines", which denotes the use of an inactivated, non-virulent form of the disease-causing organism during the vaccine preparation process.
We identified five randomised trials, which were done in Peru, India and Bangladesh. This provides high certainty evidence that two-dose administration of the whole-cell plus recombinant vaccine, Dukoral, with or without a booster dose, is effective in preventing cholera over at least two years, with an overall vaccine efficacy of 76%. Similarly, the two-dose regimen of the bivalent whole cell vaccine, specifically Shanchol, provided protection against cholera infection for up to five years, showing an overall vaccine efficacy of 80%, also with high-certainty evidence. Lastly, there was high certainty evidence that a single dose of this vaccine prevented cholera infection at the two-year follow-up, with an overall vaccine efficacy of 40%.
In regard to other cholera vaccines, it's important to note that there are no trials on some bivalent whole cell vaccines, such as Euvichol/Euvichol-Plus. However, these and the bivalent whole cell vaccine that we did find trials for, Shanchol, are considered to be functionally identical, so the findings from trials on Shanchol can be reasonably applied to Euvichol/Euvichol-Plus. This is important, because the manufacturer of Shanchol has decided to cease production of the vaccine by the end of 2023.
In summary, therefore, we found that oral killed cholera vaccines are safe and well-tolerated, with adverse events being comparable between the vaccine and placebo or no vaccine groups. Therefore, in cholera-endemic regions or during outbreaks and humanitarian crisis, the use of a bivalent whole cell vaccine, such as Shanchol or of a whole-cell plus recombinant vaccine, such as Dukoral, can effectively protect against cholera and prevent infections. Ongoing exploration of the long-term effectiveness of single-dose bivalent whole cell vaccination for up to five years is warranted, and there is a need for trials assessing the effectiveness of newer vaccines, including Hilchol.

Mike: If you would like to learn about the vaccines that have been tested in randomised trials and watch for further updates of this review if the additional evidence becomes available, you can find it online with a simple search for 'cholera vaccines' at Cochrane Library dot com.