New guidelines from the Centers for Disease and Control (CDC) stated the increasing risk from the Delta variant meant that fully vaccinated adults should wear masks in areas where coronavirus infection rates are causing concern.
But what’s the threshold? And where are the at-risk areas?
The CDC has issued a colour-coded map of the United States showing areas of low, moderate, substantial and high risk.
Anywhere with substantial or high risk are strongly advised to mask up when indoors, as new evidence suggests fully vaccinated people can still spread the virus.
"This new science is worrisome and, unfortunately, warrants an update to our recommendations," CDC director Dr Rochelle Walensky said on Tuesday.
The CDC calculates Covid risk level by anaylsing the number of new cases per 100,000 residents and the percent of coronavirus tests that come back positive in a seven-day period.
Transmission rates are considered substantial if there are 50 to 99 new cases per 100,000 residents, or if positive tests are returned on eight to nine per cent of tests.
Rates are considered high when there are 100 or more new cases per 100,000 in the past seven days and ten per cent or higher positive test results during in that period.
The map shows data at a county-by-county level and is being constantly updated.
Unvaccinated people should wear masks indoors regardless of the rate of cases in their area, the CDC advises.
Revised guidelines from the CDC also advise vaccinated people to get tested if they have been exposed to the virus, even if they aren’t showing any symptoms.
They had previously said that vaccinated people didn’t need to get tested if they had been close to an infected person unless they had symptoms.
The rate of coronavirus infections is about twice as high in Republican counties as in Democrat counties amid a surge in cases due to the Delta variant, a new analysis from The Washington Post stated.
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