Fig. 1: Summary of potential future scenarios for global SARS-CoV-2 transmission depending on the chosen global vaccine strategies and rate of immune waning following infection or vaccination.

Vaccine stockpiling and rapidly waning immunity result in low global population immunity towards SARS-CoV-2, and may prompt frequent variant emergence and booster administration. High global population immunity is achieved under scenarios characterized by equitable vaccine allocation and more durable immunity. Under these scenarios, variant emergence may be less frequent, and the need for boosters may also be reduced. Vaccine hesitancy acts similarly to vaccine inequity in leaving large portions of the population unvaccinated, lowering overall global population immunity.