Shanchol, the cholera vaccine used in endemic countries, is given in two doses 6 weeks apart. But some patients may simply not return for a second dose. If the second dose is delayed by more than 6 weeks, the WHO says, the whole regimen has to be restarted. According to a researcher at the Johns Hopkins Bloomberg School of Public Health, a single dose of Shanchol may provide sufficient protection in an epidemic. Andrew Azman used mathematical models to determine "minimum relative single-dose efficacy," the point at which a single-dose cholera vaccine campaign could be equally or more effective than a two-dose campaign in hypothetical epidemics. His models were based on outbreaks in Guinea, Zimbabwe and Haiti. And while Azman and his colleagues found evidence that a single dose of Shantha's Shanchol might be sufficient, "substantial uncertainty about one-dose efficacy remains" and field studies in areas with periodic cholera outbreaks are a priority, the team wrote. More