Masks make a comeback in some US counties 1:03
(CNN) -
Unpublished data shows that vaccinated people who are later infected with the delta variant of the coronavirus can have as much viral load as those who are not vaccinated.
This information is the main driver of the latest change to the mask guide from the US Centers for Disease Control and Prevention (CDC), according to a source involved in the process.
In general, people who received the vaccine still play a small role in transmission, and breakthrough infections are rare.
In addition, the source pointed out two other factors that led to this decision: the prevalence of the delta variant and the low vaccination rate.
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4:17
When the guideline was initially revised on May 13 so that vaccinated people could stop wearing a mask, the delta variant only accounted for 1% of reported infections.
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Now, according to the CDC, it accounts for at least 83% of cases.
The source also noted that the country's overall vaccination level is lower than initially expected.
In addition, he indicated that most of the transmission occurs in areas with vaccination levels below 40% of the population.
Delta variant