SEOUL, South Korea--The International Vaccine Institute has discovered for the first time that orally administered, killed cholera vaccines protect not only those who are vaccinated but also their unvaccinated neighbors-- a phenomenon known as "herd protection". This dual protection may make these vaccines potent tools for controlling cholera, one of the world´s most dreaded diseases. The result of the study appeared on May 24 in the online version of the Lancet, one of the world´s most renowned medical journals.
In this study IVI scientists conducted an innovative re-analysis of a 1985 trial of two oral killed cholera vaccines (cholera toxin B subunit-killed whole cell and killed whole cell only) in Bangladesh, and demonstrated that areas with higher vaccine coverage rates had markedly lower rates of cholera infections both among people who received an inactive placebo and among vaccinees. The trial targeted 124,035 people in 6,423 geographical clusters in rural Bangladesh.
The data suggest that even people who are not vaccinated themselves benefit indirectly from widespread vaccine use, because vaccination reduces the circulation of the microorganism causing cholera.
"The re-analysis of the Bangladesh trial demonstrates that the use of killed oral cholera vaccines can have a major impact on cholera transmission," said Dr. John D. Clemens, IVI Director and a world authority in vaccine evaluation. "Even if not all people in a community take the vaccine, it can be expected that outbreaks can be prevented, or if outbreaks occur, many fewer people will be affected."
Cholera, an enteric disease transmitted by fecal or oral route, kills an estimated 120,000 people worldwide every year, and it still afflicts many developing countries in Asia and Africa with unclean water and poor sanitation. Dr. Clemens said "This promising finding provides further evidence for health policymakers to vaccinate populations at high risk of cholera infections especially in the event of disasters, such as tsunamis and flooding."
This important finding follows an earlier, recently published study led by IVI scientists that showed that one of two oral killed cholera vaccines tested in Bangladesh, BS-WC (marketed by SBL Vaccin as DukorolTM) was safe and highly effective in preventing the disease in a population in Mozambique with a high prevalence of HIV/AIDS. The study was published on the February 24 issue of the New England Journal of Medicine.
The IVI is the world´s only international organization devoted exclusively to research and development of new vaccines for the poor in developing countries. It conducts field research to accelerate the introduction of vaccines in 21 developing countries of Asia, Africa and Latin America, and laboratory research to develop new vaccines at its headquarters on the campus of Seoul National University.