Comparative Effectiveness of Different Strategies of Oral Cholera Vaccination in Bangladesh: A Modeling Study

Abstract

BackgroundKilled, oral cholera vaccines have proven safe and effective, and several large-scale mass cholera vaccination efforts have demonstrated the feasibility of widespread deployment. This study uses a mathematical model of cholera transmission in Bangladesh to examine the effectiveness of potential vaccination strategies.Methods & FindingsWe developed an age-structured mathematical model of cholera transmission and calibrated it to reproduce the dynamics of cholera in Matlab, Bangladesh. We used the model to predict the effectiveness of different cholera vaccination strategies over a period of 20 years. We explored vaccination programs that targeted one of three increasingly focused age groups (the entire vaccine-eligible population of age one year and older, children of ages 1 to 14 years, or preschoolers of ages 1 to 4 years) and that could occur either as campaigns recurring every five years or as continuous ongoing vaccination efforts. Our modeling results suggest that vaccinating 70% of the population would avert 90% of cholera cases in the first year but that campaign and continuous vaccination strategies differ in effectiveness over 20 years. Maintaining 70% coverage of the population would be sufficient to prevent sustained transmission of endemic cholera in Matlab, while vaccinating periodically every five years is less effective. Selectively vaccinating children 1–14 years old would prevent the most cholera cases per vaccine administered in both campaign and continuous strategies.ConclusionsWe conclude that continuous mass vaccination would be more effective against endemic cholera than periodic campaigns. Vaccinating children averts more cases per dose than vaccinating all age groups, although vaccinating only children is unlikely to control endemic cholera in Bangladesh. Careful consideration must be made before generalizing these results to other regions.

Oral cholera vaccines and their impact on the global burden of disease

“…Using an age-structured mathematical model of endemic cholera transmission calibrated to reproduce cholera dynamics of Matlab, Bangladesh, maintaining 70% OCV coverage of residents one year and older can interrupt cholera transmission. 35 These results are consistent with an earlier model from Bangladesh suggesting that 50% coverage was sufficient to stop transmission. 36 As cholera dynamics (e.g., age-specific incidence, proportion of waterto-person transmission, degree of endemicity) can vary across nations and subnationally, these results from Bangladesh may not be straightforwardly generalizable to other nations or subnational areas.…”

The First Use of the Global Oral Cholera Vaccine Emergency Stockpile: Lessons from South Sudan

“…More work is needed in understanding how to target appropriate populations if OCV is to become more integrated into standard cholera control and prevention packages. With enhancement of cholera surveillance systems and analyses of historical epidemiologic data, target populations may be identified more precisely—whether based on geography [ 10 ], age [ 11 ], or other criteria [ 12 ]. More evidence is needed on alternative dosing strategies, and field-adapted variants of currently licensed OCV should be fast-tracked.…”

Seasonality and the effectiveness of mass vaccination

“…Pathogens with \long cycle” transmission, like cholera, may be more affected by seasonal interruption than predicted from an SIR model, which captures short cycle (person-to-person) but not long cycle (environmental) transmission. Transmission models that include long cycle transmission could be used to study seasonality of enteric pathogens [6, 5, 9], while models that explicitly include vectors, such as [22], could be used to study vector-borne pathogens. However, the SIR model is sufficient for the qualitative analyses presented here.…”