CNN reports:

In the week ending December 21, there was nearly three times as much Covid-19 circulating in the US than there was during the week ending December 7, CDC data shows.

This surge happened in all regions of the country, but there has been a particularly sharp uptick in the Midwest, where Covid-19 levels are nearly twice as high as they are in other parts of the country.

Some experts worry that the rapid rise after an unusually long lull could have left many people vulnerable to disease spread at the height of the holiday season.

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