Comparing alternative cholera vaccination strategies in Maela refugee camp: using a transmission model in public health practice

Abstract

BackgroundCholera is a major public health concern in displaced-person camps, which often contend with overcrowding and scarcity of resources. Maela, the largest and longest-standing refugee camp in Thailand, located along the Thai-Burmese border, 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 and planning for subsequent campaigns, we developed a mathematical model of cholera in Maela.MethodsWe formulated a Susceptible-Infectious-Water-Recovered-based 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). After the vaccine campaign, we generated case forecasts for the next year, to inform on-the-ground decision-making regarding whether a booster campaign was needed.ResultsWe found that preexposure vaccination can substantially reduce the risk of cholera even when <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, given that a two-dose schedule would incur a delay in administration of the second dose. Forecasting using realistic coverage levels predicted that there was no need for a booster campaign in 2014 (consistent with our predictions, there was not a cholera epidemic in 2014).ConclusionsOur analyses suggest that vaccination in conjunction with ongoing water sanitation and hygiene efforts provides an effective strategy for controlling cholera outbreaks in refugee camps. Effective preexposure vaccination depends on timing and effectiveness. If a camp is facing an 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. Overall, this analysis illustrates how mathematical models can be applied in public health practice, to assist in evaluating alternative intervention strategies and inform decision-making.

Direct transmission via households informs models of disease and intervention dynamics in cholera

“…Specifically, the nature and amount of household transmission can have a meaningful impact, not only on the trajectory of disease, but on which intervention strategies might be most effective in preventing or attenuating a given epidemic. Our results support recent findings suggesting that vaccines can be especially effective in high-density settings with large amounts of household transmission [9]. That is, water treatment and antibiotics-both of which may be relevant in other settings-are likely to be less effective in subverting epidemics in refugee camps, and related settings where household transmission is high.…”

“…Importantly, our model structure allows one to examine how different magnitudes of household transmission influence disease dynamics. A recent model of high-density settings simulated these dynamics effectively, but did so for a single refugee camp with a specific set of parameter values [9]. Our model, alternatively, explores the space of possible direct transmission parameters that may pertain to different high-density cholera settings.…”

“…We might especially expect direct household transmission to influence disease dynamics in high-density settings, like those associated with displaced populations (e.g. refugee camps) [8,9].…”

Refugee Health During COVID-19 and Future Pandemics

“…During a pandemic, this concern grows exponentially due to the frequent inability of displaced persons to escape the present pandemic’s impact. Indeed, history proves that failing to include displaced persons in pandemic response plans has left them vulnerable to the reemergence of infectious diseases, as was the case for cholera and now during the COVID-19 pandemic [ 8 – 10 ]. There is now increasing evidence that racial and ethnic minority groups, including many displaced populations, have been disproportionately affected by COVID-19 [ 10 ].…”

Optimizing one-dose and two-dose cholera vaccine allocation in outbreak settings: A modeling study

“…Between 2005 to 2012, surveillance had identified four cholera outbreaks in Maela, the largest refugee camp in Thailand with high population density and migration [7,24]. The second largest of these outbreaks occurred in 2010 with 362 confirmed cases [25]. At this time, the camp was home to approximately 45,000 refugees, and 13% were children under five years old [7,25].…”