Vaccination, like tests, is a state-led effort in the U.S.

With daily cases crossing 250,000, COVID-19 has killed nearly 380,000 people in the U.S. -- the highest in the world. As states roll out vaccines in phases amid reports of the two more transmissible variants from the UK and South Africa in the country, experts warn that arresting the virus spread is key to stopping the pandemic. ProPublica’s Caroline Chen joins Hari Sreenivasan to discuss.