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An internal Centers for Disease Control and Prevention document obtained by The Washington Post states that the Delta variant of the coronavirus appears to cause more serious infections and is as contagious as chickenpox.

The CDC reached this conclusion after looking at new, unpublished data from outside studies and outbreak investigations, the Post reports. The research also suggests that people who are vaccinated against the coronavirus but become infected by the Delta variant are able to transmit the virus just as easily as people who are not vaccinated, and it's estimated that every week, there are 35,000 symptomatic infections among the 162 million Americans who are vaccinated.

This worrying information is what triggered the CDC earlier this week to change its guidelines for vaccinated people, telling them they should wear masks indoors in COVID-19 hot spots. It's not just CDC scientists who are alarmed — in an email to the Post, Robert Wachter, chairman of the Department of Medicine at the University of California at San Francisco, said when he finished reading the document, he was "significantly more concerned than when I began."

The CDC wants people to get vaccinated and take preventative measures, like wearing masks, and acknowledged in the document that with the Delta variant in play, "the war has changed." It is critical that new messaging get out to the public emphasizing the importance of getting vaccinated, while also explaining that people who get the vaccine can still become infected by the virus, although it keeps them from getting severely ill. To help people better understand how Delta is changing the coronavirus game, an official told the Post that the CDC will publish the new data on Friday.