The new coronavirus variant has emerged as the United States grapples with a nationwide spike in infections that added more than a million new cases in just six days, according to a Reuters tally, a total of more than 18 million since the pandemic began. Many US states and cities have imposed lockdowns and business closures to try to get a handle on a wave of illness driven by last month's Thanksgiving gatherings. Political leaders have asked Americans to stay home for the upcoming holidays to prevent a surge upon the surge threatening to overwhelm healthcare systems.