The US Centres for Disease Control and Prevention is stepping up its efforts to track coronavirus mutations to ensure that Covid-19 vaccines and treatments stay ahead of new variants of the disease until collective immunity is achieved, the CDC chief said.

Dr Rochelle Walensky, who took over as CDC director last Wednesday, said the greatest immediate culprit for sluggish vaccine distribution is a supply crunch worsened by inventory confusion inherited from the Trump administration.

“The fact that we don’t know today, five days into this administration, and weeks into planning, how much vaccine we have just gives you a sense of the challenges we’ve been left with,” she told Fox News.

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