Global disparities in the introduction, scale-up, and effectiveness evaluation of COVID-19 vaccines.

The global response to COVID-19 saw the most rapid and extensive vaccination rollout in history. Yet there were large disparities in the introduction, scale-up, and evaluation of programmes. To systematically quantify these disparities, we generate linkages across public datasets containing country- and territory-level income data, COVID-19 vaccination rates, and COVID-19 vaccine effectiveness (VE). Our results show that, compared with high-income countries, lower-income countries introduced vaccines later, were less likely to achieve key coverage milestones, and were slower to do so where these milestones were achieved. The literature on primary series COVID-19 VE has been dominated by studies of mRNA vaccines from high-income countries, with data for other vaccines and lower-income countries appearing later and in substantially lower quantities. For vaccines with available VE data across multiple income settings (BNT162b2, mRNA-1273, and ChAdOx1-S), our meta-regression highlights robust protection against severe COVID-19, with no significant differences in primary series VE according to country-level income status during the Delta and Omicron periods. Our findings demonstrate the strong protection conferred by COVID-19 vaccines across diverse populations. Nonetheless, our results quantify the stark disparities that pervaded each stage of COVID-19 vaccine implementation, and highlight evidence gaps related to products and platforms being used across much of the globe.