The head of the US Centers for Disease Control and Prevention (CDC) Dr Rochelle Walensky told a White House briefing: "I’m going to reflect on the reoccurring feeling I have of impending doom," adding "we have so much reason for hope, but right now I’m scared".
Dr Walensky expressed her concerns because of a spike in Covid-19 cases in the US, the BBC reports, with 60,000 a day in the past week. The most serious outbreak has been in the north-east.
It comes despite 22% of the population having been vaccinated. However, President Biden has struggled to convince some states that face masks need to be worn, and there are widespread differences in which age groups have been vaccinated around the country.
The threat of a renewed outbreak may hamper efforts to open a UK-US travel corridor this summer. Until now, the US had been seen as a serious prospect due to the speed of its vaccination programme.
