Establishing herd immunity against Ebola through vaccination.

OBJECTIVES In response to recent concern regarding Ebola outbreaks, this study aims to (1) determine the relationship between vaccination coverage and herd immunity, (2) determine the vaccination coverage necessary to establish herd immunity for previous Ebola viruses, and (3) recommend vaccination coverage thresholds for future Ebola viruses. METHODS Herd immunity thresholds needed to block transmission of Ebola virus were determined using vaccine efficacy and number of secondary cases per infected case during an entire infectious period. RESULTS In past Ebola outbreaks 42.2-63.0% of the population would need to be vaccinated in order to prevent transmission and outbreaks. Assuming 80% vaccine efficacy as reported by phase I clinical trials, 52.7-78.7% of the population would require vaccination coverage in order to establish herd immunity. In recent ring vaccination trials which considered the vaccine to be 100% effective after 10 days, 42.2-63.0% of the population would need to be vaccinated. CONCLUSION For future Ebola outbreaks, the spread of the virus can be prevented by vaccinating certain percentages of the population depending on vaccine efficacy and number of secondary cases per infected case.