Comparing alternative cholera vaccination strategies in Maela refugee camp using a transmission model

Abstract

Background. Cholera remains a major public health concern, particularly in refugee camps, which may contend with overcrowding and scarcity of resources. Maela, the largest long-standing refugee camp in Thailand, experienced four cholera outbreaks between 2005 and 2010. In 2013, a cholera vaccine campaign was implemented in the camp. To assist in the evaluation of the campaign, we developed a mathematical model of cholera in Maela.Methodology/Principal Findings. We formulated a Susceptible-Infectious-Water-Recovered-based cholera transmission model and estimated parameters using incidence data from 2010. We next evaluated the reduction in cases conferred by several immunization strategies, varying timing, effectiveness, and resources (i.e., vaccine availability). Finally, we generated post-campaign case forecasts, to determine whether a booster campaign was needed. Using parameters from our calibrated model, our analyses suggest that preexposure vaccination can substantially reduce the risk of cholera even when the < 50% of the population is given the full two-dose series. Additionally, the preferred number of doses per person should be considered in the context of one vs. two dose effectiveness and vaccine availability. For reactive vaccination, a trade-off between timing and effectiveness was revealed, indicating that it may be beneficial to give one dose to more people rather than two doses to fewer people, which would incur a delay in administration of the second dose. Forecasting using realistic coverage levels indicated that there was no need for a booster campaign in 2014.Conclusions/Significance. Our analyses suggest that vaccination in conjunction with water sanitation and hygiene improvements provides an effective strategy for cholera outbreaks in refugee camps. Effective preexposure vaccination depends on timing and effectiveness. If a camp is facing an ongoing outbreak, delayed distribution of vaccines can substantially alter the effectiveness of reactive vaccination, suggesting that quick distribution of vaccines may be more important than ensuring every individual receives both vaccine doses. Author summaryWe developed an age-structured Susceptible-Infectious-Water-Recovered (SIWR)-based transmission model to consider different cholera vaccination strategies in Maela, the largest long-standing refugee camp in Thailand. Our model was fit to cholera incidence data from 2010 and was in part parameterized by demographic data collected from the camp. We considered multiple scenarios, including both a theoretical exploration of the effects of variation in timing, effectiveness and supply, as well as the real-world coverage of vaccine in Maela. The preferred number of doses per person and timing of vaccination campaigns should be considered in the context of one vs. two dose effectiveness and logistical constraints. Importantly, our analysis coincided with an actual cholera vaccination campaign in the camp and was used to evaluate the campaign and to help determine that there was no need for a follow-up boo...