Managing Two-Dose COVID-19 Vaccine Rollouts with Limited Supply
35 Pages Posted: 23 Feb 2021
Date Written: February 22, 2021
We consider the problem of rolling out an approved COVID-19 vaccine (e.g., the one developed by Pfizer) that requires two doses to be spaced apart by a fixed time interval. Facing severely limited supply and mounting pressure to rapidly achieve herd immunity through vaccination, the U.K. and U.S. governments, along with the E.U., face the decision of whether to reserve stocks for the required second doses for returning recipients. We model the vaccine rollout process and complement it with an SIR (susceptible-infected-recovered) model that captures the disease transmission process. For a two-dose vaccine, we model the inventory dynamics under three stocking policies: (1) holding back second doses, (2) releasing second doses, and (3) stretching the lead time between doses. Counterintuitively, we show that even if one intends to release all second doses, only less than half of the available doses can be allocated to first-dose appointments in order to avoid delays in administering the required second doses for returning recipients, no matter how quickly supply grows over time. We show analytically that under a (weakly) increasing vaccine production rate, releasing second doses reduces the number of infections but creates uneven vaccination patterns. Contrary to popular belief that releasing the required second doses will reduce infections significantly, our numerical results reveal the reduction in infections is quite modest. Compared with the policy of releasing second doses, stretching the between-dose lead time flattens the infection curve but leads to a higher total case count. Finally, we consider an alternative single-dose vaccine with a lower overall efficacy (e.g., the Johnson & Johnson vaccine) and show it can be more effective than its two-dose counterparts in slowing down infections and ending the pandemic. As more than one hundred countries have yet to start their vaccination efforts as of February 2021, our research has important policy implications for various national and local governments to develop their vaccine rollout strategies especially when their supply of vaccine will be likely to be limited initially.
Keywords: COVID-19 vaccine rollout, vaccine inventory, health policy, SIR model
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