Haiti cholera: less than 50% vaccination needed to halt spread

Researchers have used a mathematical model to show that a surprisingly low level of vaccination coverage would stem the spread of cholera in Haiti that has followed the 2010 earthquake.

The findings add fuel to an ongoing debate about the types of public health intervention that should be used to contain the epidemic.

"Even if we could get an immunization rate in the range of 40 to 50 percent, it should be possible to control recurrent cholera outbreaks," said author Glenn Morris (University of Florida, Gainesville, USA) in a press statement.

"That should be enough to tilt things in your favor so that you can start getting control of the disease in these areas, to where, hopefully, rates of transmission will slow and numbers of cases will gradually die off."

The model showed that overall vaccination coverage of 45.4% across Haiti would be sufficient to suppress transmission.

However, there is substantial geographic variation in the outbreak. The Artibonite department, which has been identified as the source of the epidemic, had the highest levels of transmission. The authors believe that this region would require 65% vaccination coverage to prevent transmission.

The researchers say that their model has advantages over earlier ones, as it incorporates recently recognized differences in the transmission pathway whereby direct human-to-human transmission in fresh stool is much more infectious than indirect transmission. Indeed, they showed that human-human transmission accounted for 68% of the disease spread.

The authors explain that Haiti's large system of estuaries could provide a long-term reservoir for cholera which, combined with human-human transmission, could lead it to become endemic.

The US Centers for Disease Control and Prevention has been skeptical about the value of cholera vaccination in Haiti, choosing to focus instead on improving the water supply and sanitation.

However, the authors conclude in Scientific Reports that large-scale vaccination, even with moderate coverage, could be effective but only if other measures are taken.

"To achieve optimal protection of the population, vaccination would need to be combined with other measures that permanently improve water systems and/or otherwise decrease the risk of transmission from environmental sources," write author Zindoga Mukandavire, University of Florida, and colleagues.

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