The Centers for Disease Control and Prevention is recommending that even vaccinated Americans resume wearing masks indoors if they are in areas with high transmissibility of the COVID-19 virus.
The guidance also recommends that people with underlying conditions that may make them more susceptible to the coronavirus wear masks, along with anyone residing with vulnerable people. Teachers, school staff, students and visitors inside schools from kindergarten to 12th grade also fall under new guidance recommending universal mask-wearking.
For vaccinated people in just under half of the counties in the country —which have high transmissibility — that means masks are recommended to be commonplace indoors once again.
Several counties with major U.S. urban centers, including Los Angeles, St. Louis and Miami-Dade, are among the high transmission counties.
Here’s what transmissibility is and how to find out if you’re in an area where you should start masking indoors again.
What is high transmissibility?
Community transmission is calculated using two metrics: how many new cases per 100,000 persons have occurred in the last seven days, and the percentage of positive diagnostic and screening nucleic acid amplification tests in the last seven days. Counties are categorized as having low, moderate, substantial or high transmissibility.
Transmissibility is considered high when there are 100 or more new cases per 100,000 in the last seven days and 10% or higher positive NAATs in that period. A high transmission designation can vary, with places like Salt Lake County in Utah at just over 100 cases per 100,000, to counties like Pulaski County in Arkansas, which has nearly 500 cases per 100,000.
The delta variant, which continues to make up more than 80% of new infections in the U.S., is more than two times as transmissible than the original strains of COVID-19, and experts believe it could cause vaccinated people to be contagious.
“This new science is worrisome and unfortunately warrants an update to our recommendations,” CDC director Dr. Rochelle Walensky said in a briefing Tuesday.
Where is COVID spreading at a high rate?
Just under half of all U.S. counties, 46.43%, are currently identified as having high COVID transmission, according to the CDC, an increase of over 17% from seven days ago.
Counties with the likelihood of substantial transmission make up 17.02% of the U.S.; 27.2% of counties are considered at a moderate level; and 9.31% are at a low level.
In two states, Florida and Arkansas, everyone should wear a mask in indoor public spaces, according to the latest CDC guidance, because each county in the two states is a high transmission community.
States with a large concentration of high transmission counties are mostly in the Southern U.S., and some Western states like Utah, according to the CDC’s COVID tracker.
In several states, including Louisiana, Mississippi, Alabama and Missouri, nearly every county is at a high level on the map.
Florida’s largest counties by population also have some of the highest levels of transmission, with Miami-Dade County at over 408 cases per 100,000 people and Broward County at 310 cases per 100,000.
Arkansas’ largest county by population, Pulaski County, has 491.18 cases of COVID-19 per 100,000 people in seven days.
Los Angeles, by comparison, is also listed in the high transmission category, and has 159.22 cases per 100,000 people over seven days. Salt Lake County in Utah has 102.63 cases per 100,000.
Transmissibility is lower in areas of the Northeast and some parts of the Midwest. Nearly all the counties in New York, Pennsylvania and Minnesota, for example, are in the moderate or low categories.
Masks are coming back:What that means for vaccinated Americans.
How to find out if you’re in a high transmissibility area
The CDC provides a COVID data tracker that includes a by-county view of transmissibility rates each week.
You can enter your state, county or metro area to find out what the transmissibility is like where you live by going to this site.