Variants Fuel Covid-19 Surge, but Scientists Voice Optimism for Vaccines

Covid-19 cases are surging across the world, fueled by highly contagious variants of the coronavirus that are popping up far from where they were first detected. The spread of these variants, scientists say, highlights how tiny, random changes in the virus’s genetic code threaten to undo progress in beating back a global pandemic that has killed at least three million people. Concerning variants are spreading in the U.S. and Canada, Europe and Latin America. Scientists say variants can be brought under control with now-familiar public health measures such as mask wearing and social distancing, despite evidence that some strains might evade the immune response triggered by vaccination or a past infection.