After a slow start, influenza is beginning to take hold across the US.

During the last week of December, some 4.1 percent of doctor visits in the U.S. were because of flu-like illnesses, according to the Centers for Disease Control and Prevention’s weekly report known as FluView. In terms of severity, that’s right in the middle of the four previous flu seasons.

Hardest hit thus far has been the southern US, covering a ten state sweep from South Carolina all the way to New Mexico and even up to Utah. Another pocket of virulence has been growing in New Jersey and New York City. So far, there’s been minimal to low levels of disease across most of the northern half of the country.

But there are several months left in the season.

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