SEOUL, Korea -- In the wake of one of the worst cholera outbreaks in more than a decade in Africa and the availability of effective vaccines, a group of international experts has called on the world health community to consider introducing oral cholera vaccines as a potential emergency measure to tackle the deadly diarrheal disease.
In their policy paper published in the May 15 issue of the journal Science, the experts, including Dr. John Clemens, Director-General of the Seoul, Korea-based International Vaccine Institute (IVI), and Prof. Robert Black at the Bloomberg School of Public Health at Johns Hopkins University in the United States, suggest that it may be the time for the world to consider potential use of oral cholera vaccines as another option for containing cholera outbreak.
Cholera remains an important public health problem in the developing world. In 2007, 177,963 cholera cases and 4,031 deaths were reported to WHO from 53 countries, with 94 percent of cases reported from Africa. The true figures are likely to be much higher, due to under-reporting, and as many as 120,000 deaths are estimated to occur each year from the disease. A recent outbreak in Zimbabwe has infected 97,979 people as of May 15, killing 4,273 since last August.
The cholera control strategy has changed little over the past decades. Oral (ORT) and intravenous rehydration therapy has been the centerpiece for rehydrating people infected with cholera. Provision of safe water and adequate sanitation were widely employed as emergency measures for people at immediate risk of cholera infection, but are not guaranteed to remain once the outbreak ends.
An oral cholera vaccine called ‘rBS-WC,’ evaluated in Mozambique by the IVI in 2004, showed about 90 percent protection against cholera of life-threatening severity, even in a population with a high prevalence of HIV. Internationally licensed and available, the vaccine has also been shown to protect unvaccinated neighbors of vaccinees through “herd protection” against cholera.
Nevertheless, vaccination has not been recommended by the World Health Organization (WHO) as a strategy to contain cholera in Zimbabwe “due to its two dose regimen, short shelf-life, high cost, and need for cold chain distribution.” There are certainly logistical complexities to administering a two-dose regimen in a setting as chaotic as Zimbabwe, as well as strategic choices to be made for how to target high risk groups for vaccination. But delivery of this vaccine has been shown to be feasible in three WHO-sponsored community demonstration projects in rural and urban sub-Saharan Africa.
Moreover, a potentially cheaper vaccine, which was developed by the IVI in collaboration with VaBiotech in Vietnam, was licensed in India last February. The vaccine’s licensure in India whose regulatory authority is WHO-approved paves the way for the worldwide use of the world’s first low-cost cholera vaccine that is suitable for use in developing countries, where most cholera cases occur. Initial results of a phase 3 study of the killed whole-cell (WC) vaccine, which enrolled 67,000 individuals in Kolkata, India in 2006, found the vaccine to confer substantial protection during two years of follow-up, including protection of children aged 1–5 years.
Dr. Clemens said, “If current barriers to potential use of oral cholera vaccines could be overcome, public health workers, Ministries of Health, international organizations and donor groups could begin a constructive discussion about how, when, and where the vaccine could be deployed.”
The International Vaccine Institute (IVI), based in Seoul, Korea, is the world’s only international organization devoted exclusively to developing and introducing new and improved vaccines to protect the world’s poorest people, especially children in developing countries. Established as an initiative of the United Nations Development Program in 1997, the IVI operates under a treaty signed by 40 countries and the World Health Organization. The Institute conducts research in 28 countries of Asia, Africa and Latin America on vaccines against diarrheal infections, bacterial meningitis and pneumonia, as well as Japanese encephalitis and dengue fever, and develops new and improved vaccines, adjuvants and assays at its headquarters in Seoul. For more information, please visit www.ivi.int