Cholera vaccine: new preventive tool for endemic countries.

Cholera is a major global public health problem and remains an important threat in almost every developing country, especially in areas where population overcrowding and poor sanitation are common, such as slums and refugee camps. Cholera is one of the most dreaded diseases in the world, in some cases leading to death within 24 h if left untreated. Without treatment, severe infection has a mortality rate of 30-50%. In 2007, WHO recorded 177,963 cholera cases and 4,031 deaths worldwide. However, the estimated actual burden of cholera is in the vicinity of 3 to 5 million cases and 100,000 to 130,000 deaths per year. The disease is endemic to parts of Africa, Asia, the Middle East and South America. Large outbreaks are common after natural disasters or in populations displaced by war, where there is inadequate sewage disposal and contaminated water. In India, during the 10-y period (1997-2006) studied, the states having the highest number of reported outbreaks were West Bengal, Orissa, Maharashtra and Kerala, which together accounted for 60% of all reported outbreaks. A review of cholera cases in India reported to WHO from 2003-2007 showed that the numbers were in the few thousands with a case fatality rate of < 1%. However, it is believed that the number of cholera cases and deaths occurring annually in India is much greater than the number reported. A literature review covering a four-year period from 2003 to 2006 found reported cholera outbreaks in 18 of the 35 States and Union Territories of India. Of these, 11 had cholera outbreaks reported for multiple years. Vietnam has produced a cheaper variant of killed whole-cell vaccine devoid of the B subunit. This vaccine contains both Vibrio cholerae O1 and O139, and provides 50 per cent protection for at least three years after vaccination. For endemic cholera, population-level immunity is relatively high, making control possible with relatively low vaccine coverage levels. This vaccine should be used in areas where cholera is endemic, particularly in those at risk of outbreaks, in conjunction with other prevention and control strategies.