Fractional Dosing of Yellow Fever Vaccine to Extend Supply: A Modeling Study

Wu, Joseph T.; Peak, Corey M.; Leung, Gabriel M.; Lipsitch, Marc

We have considered fractional dosing for residents of areas at high risk for transmission. Another group of interest are travelers, for whom we must also consider longevity of response, lower levels of exposure, and more detailed discussions on equity outside the scope of this modeling paper. The cost of fractional-dose strategies will depend on the route of administration, but could potentially be substantially less expensive per vaccine recipient. 18 Our simple model has several limitations. We assume homogeneous mixing of the population (reasonable at least locally for a vector-borne disease). We also fix a particular value of R 0 for each calculation, and assume this value is maintained until the epidemic has swept through a population. In reality, R 0 will vary seasonally as vector abundance, extrinsic incubation period, and other factors vary. The existence of a hightransmission season might enhance the benefits of fractional-dose vaccination. Most importantly, there will be a premium on achieving high vaccine coverage before the peak of transmission to maximally impact transmission, and this will be limited by supply constraints that could be partially relieved by fractionation. However, the cases-averted estimates might not all be achieved in a single transmission season if seasonal declines in mosquito abundance abrogate transmission before the large majority of the population has become infected.