A new study finds that cases of a more contagious coronavirus variant are rapidly increasing in the United States, and significant community transmission may already be occurring. Although the B.1.1.7 variant first identified in the UK is currently at a relatively low frequency in the United States, the paper says it's doubling every week and a half, similar to what was observed in other countries. The report estimates this variant is 35-45% more transmissible than strains that appeared earlier in the US, and it's doubling about every 10 days in the country.