South Africa has halted plans to roll out the Oxford-AstraZeneca vaccine after it showed minimal efficacy in preventing mild and moderate COVID-19 in people infected by the dominant coronavirus variant which has been overwhelming South Africa’s health system. Meanwhile, the British government moved to reassure the public that the Oxford-AstraZeneca vaccine prevents death and severe illness and is effective against the variant that’s come to dominate cases in the U.K.

The U.S. Centers for Disease Control and Prevention has identified nearly 700 U.S. infections from variants first reported in the U.K., South Africa and Brazil that may have evolved to spread more rapidly — or to reinfect people who have already had COVID-19.