Covid-19 cases in the US may be trending in the right direction, but experts say there's still reason to worry. For one, there are new variants circulating in the US that are threatening another surge and could make even everyday activities more dangerous. Cases of a variant first spotted in the UK have been detected in at least 28 states, new data from the CDC shows. And Minnesota officials recently announced the first US case of another variant, detected in a traveler from Brazil.