Rapid and localised vaccinations can prevent a Cholera epidemic

Responding to a cholera epidemic with an intervention that includes vaccines and water treatment in the immediate vicinity of the first cases leads to a reduction of infections of up to 81% compared to a large-scale campaign.

To understand and demonstrate this, an international team of mathematical model designers, experts in public health and doctors analysed the high-resolution data of an epidemic that hit N’djamena (in the NASA satellite photo), capital of Chad, in 2011. The results were published on the PLOS Medicine scientific journal. Among the authors Enrico Bertuzzo professor of Ecohydrology at the Department of Environmental Sciences, Informatics and Statistics at Ca’ Foscari, has overseen the development of the modelling approach.

“Immediately intervening in the area where the first cases appear,” explains Enrico Bertuzzo, “can prevent the spread of the epidemic. Furthermore, this technique requires fewer resources than large-scale action, which we have seen would be less effective.”

To test the hypotheses, the team led by Andrew Azman from the Johns Hopkins University in the US, modeled the cholera epidemic in Chad that infected 4,352 people over 232 days. Starting from the data on the development of the epidemic and the spatio-temporal distribution of cases, scientists have proven the effectiveness of a response that focuses on a 100 metre radius around the reported cases.

To be efficient, the intervention should be composed of a combination of actions: the provision of clean drinking water and the oral admission of vaccines and antibiotic prophylaxis.

Cholera is principally contracted from the consumption of contaminated food or water and the epidemics are linked to insufficient hygiene, overcrowding, inadequate sanitary facilities and non-potable water.

In recent years, the number of known cases on a global level varies from 110 thousand to 200 thousand per year. Officially, 5 thousand deaths per year are due to cholera, but the World Health Organisation estimates that the real number may be significantly greater, due to the lack of reporting and deficiencies in surveillance systems.