Projected Impact of Vaccination Timing and Dose Availability on the Course of the 2014 West African Ebola Epidemic

PLOS CURRENT OUTBREAKS                                                                              Nov. 21, 2014
By David Fisman and Ashleigh Tuite, Dalla Lana School of Public Health, University of Toronto

As removal of population-level susceptibility through vaccination could be a highly impactful control measure for this epidemic, we sought to estimate the number of vaccine doses and timing of vaccine administration required to reduce the epidemic size. Our base model was fit using the IDEA approach, a single equation model that has been successful to date in describing Ebola growth. We projected the future course of the Ebola epidemic using this model. Vaccination was assumed to reduce the effective reproductive number. We evaluated the potential impact of vaccination on epidemic trajectory under different assumptions around timing of vaccine availability.

Results: Using effective reproductive (Re) number estimates derived from this model, we estimate that 3-4 million doses of vaccine, if available and administered, could reduce Re to 0.9 in the interval from January-March 2015. Later vaccination would be associated with a progressively diminishing impact on final epidemic size; in particular, vaccination to the same Re at or after the epidemic is projected to peak (April-May 2015) would have little impact on final epidemic size, though more intensive campaigns (e.g., Re reduced to 0.5) could still be effective if initiated by summer 2015. In summary, there is a closing window of opportunity for the use of vaccine as a tool for Ebola epidemic control.

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http://currents.plos.org/outbreaks/article/projected-impact-of-vaccination-timing-and-dose-availability-on-the-course-of-the-2014-west-african-ebola-epidemic/