Vaccine rollout has been uneven across countries and in time, despite pronouncements of urgency from leaders of wealthy nations and the establishment of initiatives such as COVAX. The global situation remains dire, with high incidence rates and a potential for sustained outbreaks in low-income and middle-income countries.
The global availability of vaccines has been limited, with states and territories being largely responsible for local distribution efforts. Because the quantity of vaccines available is finite, strategies are needed to prioritize vaccination and balance the need for a large number of doses with the desire to protect vulnerable populations.
Currently, most states are using an age-based approach to vaccination, where the oldest are vaccinated first, followed by essential workers and then by everyone else. The rationale behind this strategy is that the risk of severe outcomes (infection, disease, and death) from the vaccine increases rapidly with age.
However, as the supply of vaccines is limited, the Advisory Committee on Immunization Practices recommends taking a phased approach to vaccination, with priority given to healthcare personnel, long-term care facility residents, and frontline essential workers. The phased strategy is not being implemented in many states, with a large number of counties having limited capacity due to lack of pharmacy access, leading to crowded clinics and delays in scheduling appointments.
We used an agent-based model with a detailed social contact network to explore how prioritization could be optimized during the vaccine rollout, considering different age groups and their likelihood of encountering each other. In addition to evaluating the impact of varying the vaccine rollout strategies, we also evaluated their effects on costs and benefits. The results show that faster vaccine rollout rates are associated with lower total cost per vaccine unit, due to fixed costs being spread over more doses.