Cholera Vaccine

NAIROBI (IRIN) - Trials of a cholera vaccine manufactured in Vietnam at a cost of only about US 20 cents a dose have produced encouraging results, especially for children, according to a press statement from the United Nations' World Health Organisation (WHO) on Friday, 8 February.

The research team concluded that the vaccine was "safe and immunogenic" and "could elicit robust immune responses", especially in children, for whom the risk of endemic cholera is highest, but also in adults, WHO stated.

The research results were encouraging, "particularly because of its low cost of production", it quoted the research scientists as saying in the latest issue of the Bulletin of the World Health Organisation. Further studies were needed in order to evaluate the clinical protection it confers, the researchers added.

Cholera, one of the key indicators of social development, no longer poses a threat to countries with a minimum standard of healthy living conditions, but remains a challenge to countries where access to safe drinking-water and adequate sanitation are not assured, according to the International Federation of Red Cross and Red Crescent Societies.

"Cholera epidemics are a marker for poverty and lack of basic sanitation," according to the US government's Centers for Disease Control and Prevention. "Lack of access to basic water and sanitation is often associated with poverty and the poor often pay more for an inaccessible supply of small volumes of water of doubtful quality," according to the WHO.   Transmitted through the ingestion of the bacteria Vibrio cholerae from the faeces of an infected person, the disease is spread generally through inadequate human-waste disposal and sanitation, contamination of water sources and/or poor personal hygiene and the contamination of foodstuffs. 

Most people infected with Vibrio cholerae do not become ill, and even when illness does occur, infection causes only mild or moderate diarrhoea in more than 90 percent of episodes, according to the WHO. However, in some 5 to 10 percent of cases, "patients develop very severe watery diarrhoea and vomiting from six hours to five days after exposure to the bacterium", it added.

In these cases, the loss of large amounts of fluid can rapidly lead to severe dehydration and, in the absence of adequate treatment - the most important of which is early rehydration - death can occur within hours.

The number of cholera cases notified by Africa exceeds by far the number of cases reported from other continents, with 27 countries reporting outbreaks in the year 2000, according to international epidemiological records.

The disease can spread rapidly in areas where sewage and drinking water supplies are inadequately treated - as is common in many areas of sub-Saharan Africa - and the situation is often exacerbated by heavy rains and flooding, conflict-related destruction of infrastructure or natural disasters, according to humanitarian sources.   

In addition to human suffering, deaths and serious public health problems, cholera can have a severe social and economic impact, according to the WHO. Furthermore, outbreaks can cause panic, often leading to inappropriate responses such as restrictions on travel and trade, quarantine or excessive isolation of affected populations.

Sudden, large outbreaks are usually caused by a contaminated water supply and, in endemic areas, cholera particularly affects young children. When cholera appears in a community, it is essential to ensure three things: the hygienic disposal of human waste; an adequate supply of safe drinking water; and good food hygiene, according to the WHO.

"The greatest risk occurs in overpopulated communities and refugee settings characterised by poor sanitation and unsafe drinking water," according to the Global Task Force on Cholera Control in Geneva, Switzerland.

The current global cholera pandemic began in Indonesia in 1961, spread to West Africa in 1970 and has now become endemic in most of the African continent, according to health officials.    

In late 1997, there was a sudden increase in the instances of cholera in the Horn of Africa, and this continued through 1998 (coincidental with regional El-Nino flooding), spreading also to many other countries. During 1998, there were major cholera outbreaks in the Democratic Republic of the Congo, Kenya, Mozambique, Uganda and Tanzania, as well as a large increase in the number of reported cases in West Africa.   In 1998, Africa reported 211,748 cases of cholera (the highest number of cases ever reported, up 79 percent on the 1997 figures) and accounted for 72 percent of the global cholera disease burden. In addition, given poor functioning of surveillance systems and inadequate data in some countries, WHO estimated that there were "many more cholera cases than the number reported".

A serious outbreak in Zanzibar meant that Tanzania had the highest number of cases of cholera in Africa for the second year running, with 43,000 cases (up from 40,249 in 1997) - followed by Uganda (18,000), Kenya (18,000) and Somalia (14,708).

A severe outbreak in Kwazulu-Natal Province, South Africa, in August 2000 gave rise to over 106,000 cases of cholera and over 230 deaths by 8 August 2001, in the biggest outbreak in Africa for that period, according to WHO statistics. All in all, the South African outbreak accounted for 80 percent of all cases worldwide in the reporting period.

There was also a severe outbreak in Kano State, Nigeria, in November 2001, with over 2,000 cases and 20 deaths reported. That followed outbreaks in Burkina Faso, Cote d'Ivoire (with over 3,000 cases) and Guinea between July and September 2001. 

When a community is unprepared for a cholera epidemic, case-fatality rates can be as high as 50 percent - usually because treatment begins too late, or there are no treatment facilities - but a well-organised response in countries geared up for treating diarrhoeal diseases can limit the case-fatality rate to less than 1 percent, according to WHO. 

"Almost every developing country is now facing either a cholera outbreak or the threat of an epidemic," according to the agency, and better, more timely information should be used to provide more rational responses to the disease, ensuring preparedness, early detection and rapid response to outbreaks.

There was a lot of work currently taking place in the effort to develop a cholera vaccine, which caused high morbidity [ill health] and mortality [death] in areas of poor medical and public health infrastructure, such as rural areas of Africa, a WHO official told IRIN on Tuesday.

The development of a new vaccine with better protective qualities, with proven effectiveness in large populations and the delivery of which was not prohibitively expensive would definitely be helpful in reducing the burden of disease in Africa, he said.

Key issues would include the duration of effectiveness of a vaccine, whether or not there were other, complicating factors in a given situation and the ease/cost-effectiveness of delivery mechanisms. At a wider level, such a vaccine would only be an adjunct to other preventive measures and cholera would never be eradicated without tackling the root causes, he added.

With increased urbanisation, cholera will be an increasing problem in the future in areas where sanitation and water safety are inadequate, according to the Red Cross Federation. Yet, current responses to cholera tend to be reactive, and more importance needs to be given to medium- and long-term prevention measures. 

Six thousand people, mostly in Africa, die daily from diseases caused by poor sanitation while another 300 million on the continent have no access to clean water, Dr Klaus Toepfer, Executive Director of the United Nations Environment Programme, stated recently. The biggest challenge to UNEP is to develop mechanisms that may ensure the survival and well-being of millions of people dying or getting ill due to the overwhelming poor sanitation, he added.

The continuing prevalence of cholera in Africa should be "a powerful stimulus to develop needed infrastructure for sanitation and for public health in general, including improvements in sanitation, safer water handling, and public health capacity for surveillance and response to epidemics", according to the US Centers for Disease Control and Prevention.

 

February 2002