A study of genomes from 33 African nations and two “overseas territories,” published in the journal Science on Thursday, tracks the evolution of the pandemic across the continent and the emergence of a number of so-called Variants of Concern and Variants of Interest. One of those, beta, spread around the globe earlier this year and rendered some vaccines partially ineffective.

The “slow rollout of vaccines in most African countries creates an environment in which the virus can replicate and evolve,” the organizations said. “This will almost certainly produce additional VOCs, any of which could derail the global fight against Covid-19.”