Meta-analysis confirms effectiveness of killed oral cholera vaccines

Last Updated: 2017-07-31

By Anne Harding

NEW YORK (Reuters Health) - Two doses of killed whole-cell oral cholera vaccine (kOCV) protect against cholera for at least three years, while a single-dose provides short-term protection, according to a new systematic review and meta-analysis.

"We now have a solid evidence base to show it indeed provides high levels of protection against cholera for at least three years, if not longer," Dr. Andrew S. Azman of the Johns Hopkins School of Public Health in Baltimore, one of the study's authors, told Reuters Health in a telephone interview. "When vaccine supply is limited, as it currently is, using one dose to quickly protect more people can be a useful option in epidemics like the one currently ravaging Yemen."

Studies have found a wide range of efficacy and effectiveness for kOCVs, which have been in use since the 1970s, Dr. Azman and his team note in their report in The Lancet Infectious Diseases, online July 17.

To gauge average efficacy and effectiveness, the researchers looked at seven trials (including 695 cholera cases) and six observational studies (with 217 cholera cases).

They defined vaccine efficacy as the relative reduction in medically attended confirmed cholera risk in randomized trial participants who received the vaccine versus those who did not. They defined vaccine effectiveness as the relative reduction in risk among vaccinated versus unvaccinated individuals in case-control, cohort, or case-cohort studies.

Efficacy of the two-dose regimen averaged 58%, while effectiveness was 76%. For children younger than age 5, two-dose efficacy was 30%, while it was 64% for children age 5 or older. Efficacy estimates for the two-dose regimen remained the same for the first two years after vaccination, and dropped to 39% at three years and 26% at four years.

Previous research on the kOCV had been done mostly in South Asia, Dr. Azman noted. "It's quite a unique setting where it's hyperendemic, and there the vaccine may actually protect differently than in other places," he said. "Now we've seen in sub-Saharan Africa, Vietnam, Peru, Haiti, in addition to India and Bangladesh, that the vaccine does consistently provide protection."

Although water, sanitation and hygiene (WaSH) interventions are believed to be the most effective approach to controlling cholera, implementing them requires investment in infrastructure as well as changes in behavior, Dr. Suman Kanungo and Dr. Pranab Chatterjee of the Indian Council of Medical Research at the National Institute of Cholera and Enteric Diseases in Kolkata write in an editorial accompanying the study. "Keeping these issues in mind, cheap and effective OCVs emerge as a viable option to keep cholera at bay, reducing morbidity and mortality, while the definitive WaSH interventions are identified and rolled out," they add.

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Lancet Infect Dis 2017