Cholera vaccines 'effective even after outbreak begins'
[SANTIAGO] Cholera vaccination could save lives and help limit epidemics even when rolled out weeks after the outbreaks start, two studies have found.
Although the WHO currently recommends considering vaccination in outbreaks, it says that there is a lack of evidence that such 'retroactive' vaccination is beneficial.
But the new studies — published in PLoS Neglected Tropical Diseases yesterday (25 January) — show for the first time that vaccination can reduce case numbers and save lives during cholera outbreaks, adding weight to calls to start vaccinating in Haiti.
The Haiti outbreak, which started in October following destruction left by the January 2010 earthquake, has affected over 190,000 people and killed almost 4,000.
One of the studies estimated that up to 40 per cent of deaths could have been prevented in Zimbabwe, during an outbreak in 2008, if a rapid vaccination response with Dukoral vaccine had reached half of the population.
Rita Reyburn, co-author of the study and a researcher at the International Vaccine Institute in South Korea, told SciDev.Net that in both settings a breakdown of infrastructure preceded the outbreak.
Until sanitation and water supply are dramatically improved in Haiti, Reyburn said, "mass vaccination campaigns with oral cholera vaccines are the most promising help that we can offer … [they] would almost certainly reduce the number of cases in the future".
But Andrea Vicari, immunisation advisor for the Pan American Health Organization's Family and Community Health section, told SciDev.Net that the findings do not change the WHO's appraisal.
He said that the assumption in Reyburn's paper that millions of vaccines doses could be made available within a few weeks are unrealistic — and vaccinating enough Haitians would take a long time, making its impact less effective.
"Haiti's outbreak is arguably much more explosive than the epidemic case of Zimbabwe modelled in the paper," he said.
The second study found that deploying ORC-Vax — a modified version of which is now licensed in India as Shanchol — following a 2008 outbreak in Hanoi, Vietnam, provided 76 per cent protection against cholera.
But Anna Lopez, one of the study's authors, and a researcher at the International Vaccine Institute in South Korea said further evidence is needed to recommend retroactive vaccination as routine, since the study was limited by its small sample size.
"Unfortunately, it is difficult to conduct studies in the middle of a cholera outbreak, as we have to prioritise care for the patients."
She said that if a vaccination campaign was conducted in Haiti, "it should be planned with appropriate lead time as it may take a while for the manufacturers to have the vaccines available for a campaign".
PLoS Neglected Tropical Diseases doi: 10.1371/journal.pntd.0000952
PLoS Neglected Tropical Diseases doi: 10.1371/journal.pntd.0001006