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COVID-19 now spreading at 'substantial' and 'high' levels in 35 Minnesota counties

Updated CDC guidelines say to mask up indoors if you live in these areas. Even if you're vaccinated.

MINNESOTA, USA — A national map updated Friday by the Centers for Disease Control and Prevention shows the number of Minnesota counties with substantial or high levels of community COVID transmission increased within a matter of days.

Earlier this week, 21 Minnesota counties fell into those categories. Now, 32 counties are at substantial levels and three counties are at high levels within the state. 

While Hennepin County and Ramsey County are at substantial levels, Lake County, Morrison County, and Dodge County are at high levels.

Fully vaccinated people living in any of these areas should wear a mask in public indoor settings, the CDC announced in its updated guidance Tuesday.

"I know this is not a message America wants to hear," CDC director Dr. Rochelle Walensky said at the time.

As numbers were updated Friday, new insight also became available.

NBC News obtained an internal CDC document that says even vaccinated people are able to readily spread the delta variant of the virus and that the variant is as contagious as the chicken pox.

However, the agency notes that vaccination does protect against more severe symptoms.

Dr. Ruth Lynfield, MD, from the Minnesota Department of Health weighed in on what these developments mean.

"We do think (the) vaccine is working very well," Lynfield said. "What was new and different is, when the amount of virus that people were carrying was looked at, it's a very high level of virus with this variant and that's why it's more contagious."

She says people who did have vaccine breakthrough - even if they didn't have a lot of symptoms - were still carrying a lot of virus in their throat and nose.

"That is why we wanted to be sure to protect the community," Lynfield said. "That when there are high levels of virus circulating - when it is so-called raining COVID - it would be a good idea for everyone to wear a mask to decrease the amount of virus because what's going to get us out of this pandemic is, if we can stop the virus circulating."

"And the vaccine, again, is a really great tool."

RELATED: CDC document warns delta variant appears to be as contagious as chickenpox

RELATED: The CDC recommends wearing masks indoors in these Minnesota counties