Mass cholera vaccination early in outbreak could stem spread of disease, studies show

Jan 27 2011

"The cholera bacterium has undergone important mutations in recent years, causing longer outbreaks of the disease with increased fatalities, researchers reported on Wednesday," Reuters reports. "In a package of papers published in the journal PLoS Neglected Tropical Diseases, they said mass vaccinations should be considered as a solution even after outbreaks have begun," the news service writes (Lyn, 1/26).

"Although easily administered oral vaccines exist, public health officials typically don't vaccinate against cholera in the throes of an outbreak because medical workers have their hands full rehydrating patients who have come down with the diarrheal disease," Science News writes (Seppa, 1/25). In recent months, the debate over how useful a cholera vaccine can be during an outbreak has "reignited," as experts try to slow the spread of the disease in Haiti, which to date has sickened some 105,000 and killed more than 2,000, Reuters writes.

"Caused by a water-borne bacteria called vibrio cholera, [cholera] is transmitted when contaminated human fecal matter gets into water, food or onto someone's hands" - a particular "challenge to countries without safe drinking water and adequate sanitation," Reuters continues. While the symptoms from the disease can kill some within hours, others "show no symptoms but can pass the bacterium further" (1/26).

In an effort to assess how a cholera vaccine could have affected the outcome of previous cholera outbreaks, "scientists collected information from three regions where cholera has struck in the past 15 years — Zimbabwe, Zanzibar and India," and used a computer model to predict outcomes of an early vaccine effort, Science News writes of one of the studies published in the journal (1/25).

In the case of cholera outbreak that took place in Zimbabwe between 2008 and  2009, during which 98,591 cholera cases had been reported with 4,288 deaths attributed to cholera, "[i]f a rapid response had taken place and half of the population had been vaccinated once the first 400 cases had occurred, as many as 34,900 (40%) cholera cases and 1,695 deaths (40%) could have been prevented," the authors of the study report. "In the sites with endemic cholera, Kolkata and Zanzibar, a significant number of cases could have been prevented but the impact would have been less dramatic," they add (Reyburn et al., 1/25).

"The PLoS package also included a study from Vietnam, which showed how mass vaccination helped control the disease in Hanoi even after an outbreak occurred in 2007," Reuters adds. "Fifteen percent of patients given the oral vaccine came down with cholera subsequently, compared to 30 percent of those not vaccinated," the authors reported, according to the news service (1/25).

"The recent outbreaks of cholera in Haiti, Pakistan, and Zimbabwe suggest that our current global action plans against cholera are failing," Edward Ryan, of Massachusetts General Hospital and Harvard University, who was not involved in the two PLoS studies, writes in an editorial where he describes how vibrio cholerae has evolved in a manner that allows it to linger, allowing for longer outbreaks of the disease. "What role cholera vaccine will play, if any, is still uncertain, and even if cholera vaccine is incorporated into response plans, many logistic hurdles would remain (who will pay, will vaccine be stockpiled, which vaccine would be used, who would control its use, delivery, and deployment, how will a vaccine program synergize with other response efforts and immunization efforts, etc.). But one thing is very clear … we have a wily and adaptive foe that has changed the rules of engagement repetitively, and it may be time for us to similarly adapt our strategies," Ryan concludes (1/25).

According to Reuters, "There are only about 200,000 to 300,000 doses of cholera vaccine available in the world, and only two companies produce it"  (1/26).