The arrival of the omicron variant of the coronavirus has health officials in some U.S. communities reviving contact tracing operations in an attempt to slow and understand its spread. In New York City, officials quickly reached out to a man who tested positive for the variant and had attended an anime convention along with more than 50,000 people last month. Other urgent tracing efforts are taking place from Nebraska to Philadelphia to Baltimore. So far the variant has been detected in a handful of states, including California, Hawaii and Colorado. Scientists are still studying how contagious omicron is and whether it can thwart vaccines.