Population-Level Effect of Cholera Vaccine on Displaced Populations, South Sudan, 2014

Abstract

Following mass population displacements in South Sudan, preventive cholera vaccination campaigns were conducted in displaced persons camps before a 2014 cholera outbreak. We compare cholera transmission in vaccinated and unvaccinated areas and show vaccination likely halted transmission within vaccinated areas, illustrating the potential for oral cholera vaccine to stop cholera transmission in vulnerable populations.

Prolonging herd immunity to cholera via vaccination: Accounting for human mobility and waning vaccine effects

“…These findings are within the range of estimates derived from South Sudan in 2014. [37] Assuming this pre-vaccination estimate of R 0 = 1.80, we find that after vaccination the probability of an outbreak first exceeded 50% in May 2016 and reached 57% when the outbreak began in October ( Fig 5C, black line). Using a "Mass and Maintain" strategy including vaccination of 100% of individuals migrating into the camp after the second mass vaccination campaign, we estimate that only 52% of the population would have been susceptible on the date the first case was reported in the camp, which is low enough to generate herd immunity at the time (assuming R 0 = 1.80)(S7 Fig).…”

“…PoC Camp between October, 2016, and January, 2017. Using the daily case counts (grey bars) and a generation interval with median of 5 days and following a gamma distribution with shape = 0.5 and rate = 0.1 as per ref [37], we report a mean time-dependent reproductive number (red line) above unity for nearly two months. 95% confidence intervals are shown in pink.…”

“…In order to estimate the probability of an outbreak given introduction of a cholera case using the population susceptibility over time, X(t), we must estimate the basic reproductive number, R 0 . Following frameworks [35,36] recently applied to cholera in South Sudan, [37] we retrospectively estimate the time-varying reproductive number using two sources: (1) daily case reports, which we extract from Cholera Situation Reports from the South Sudan Ministry of Health, [38] and (2) an expected generation interval distribution, which we assume to follow a discretized gamma distribution with median of 5 days. [37] This method assumes uniform mixing, no imported cases after the first case, and no missing data.…”

“…Following frameworks [35,36] recently applied to cholera in South Sudan, [37] we retrospectively estimate the time-varying reproductive number using two sources: (1) daily case reports, which we extract from Cholera Situation Reports from the South Sudan Ministry of Health, [38] and (2) an expected generation interval distribution, which we assume to follow a discretized gamma distribution with median of 5 days. [37] This method assumes uniform mixing, no imported cases after the first case, and no missing data. [35,36] Maximum likelihood estimation procedures were implemented in the statistical software program R using the R0 package.…”

Adapting to the global shortage of cholera vaccines: targeted single dose cholera vaccine in response to an outbreak in South Sudan

“…5,7,9,[13][14][15][16] However, providing just one dose per person would allow double the number of people to be vaccinated, and could potentially increase population-wide protection (herd immunity), thereby having a greater eff ect on public health. 17 On the basis of this information, alongside promising initial results from a large single-dose clinical trial 15 presented in a scientifi c meeting at the time of the outbreak, the decision was taken to target a larger atrisk population with a single dose of oral cholera vaccine (Shanchol). After wider consultations with key stakeholders, the Ministry of Health, supported by Médecins Sans Frontières, requested 640 000 doses to cover Juba and Torit counties.…”