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

Abstract

BackgroundOral cholera vaccination is an approach to preventing outbreaks in at-risk settings and controlling cholera in endemic settings. However, vaccine-derived herd immunity may be short-lived due to interactions between human mobility and imperfect or waning vaccine efficacy. As the supply and utilization of oral cholera vaccines grows, critical questions related to herd immunity are emerging, including: who should be targeted; when should revaccination be performed; and why have cholera outbreaks occurred in recently vaccinated populations?Methods and findingsWe use mathematical models to simulate routine and mass oral cholera vaccination in populations with varying degrees of migration, transmission intensity, and vaccine coverage. We show that migration and waning vaccine efficacy strongly influence the duration of herd immunity while birth and death rates have relatively minimal impacts. As compared to either periodic mass vaccination or routine vaccination alone, a community could be protected longer by a blended “Mass and Maintain” strategy. We show that vaccination may be best targeted at populations with intermediate degrees of mobility as compared to communities with very high or very low population turnover. Using a case study of an internally displaced person camp in South Sudan which underwent high-coverage mass vaccination in 2014 and 2015, we show that waning vaccine direct effects and high population turnover rendered the camp over 80% susceptible at the time of the cholera outbreak beginning in October 2016.ConclusionsOral cholera vaccines can be powerful tools for quickly protecting a population for a period of time that depends critically on vaccine coverage, vaccine efficacy over time, and the rate of population turnover through human mobility. Due to waning herd immunity, epidemics in vaccinated communities are possible but become less likely through complementary interventions or data-driven revaccination strategies.

Vaccine hesitancy and the resurgence of vaccine preventable diseases: the way forward for Malaysia, a Southeast Asian country

“…28 Secondly, in countries with high vaccination rates, like Malaysia, vaccine-derived herd immunity may be shortlived due to high rate of human mobility, and the influx of international travelers and migrants. 29,30 Presently, vaccination coverage of migrants is not monitored, exposing a gap in the NIP. There is recommendation from the study that children of migrants should also be included in the NIP as this would also contribute toward protection of the local children from being affected by VPDs.…”

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

“…Another used an agent-based model to examine cholera transmission in a refugee camp setting [44], and one mathematical modeling analysis included displaced-persons to examine cholera dynamics and rainfall in Haiti using a model accounting for environmental transmission [39]. Finally, another used compartmental models to examine cholera transmission and vaccination–induced herd immunity among displaced persons in South Sudan [45]. These models have been useful in explaining different drivers of transmission across settings and evaluating proposed interventions.…”

The use of mobile phone data to inform analysis of COVID-19 pandemic epidemiology

“…These data can be collected in high-and low-income settings and can capture, in near real-time, changes in mobility and clustering patterns for large swaths of the population. We and others have previously used aggregated and anonymized geolocation information from passively collected mobile phone data to successfully inform and model the spatial and temporal dynamics of endemic and emerging infectious diseases, including malaria [13][14][15][16] , cholera 17 , measles [18][19][20][21][22][23] , dengue 24,25 , and Ebola 26,27 . Through these prior applications, an understanding of privacy-conscious ways to utilize these data and inform public health policy while forming productive collaborations with operators, public health officials, and academic partners has been developed.…”