CHICAGO (CBS) -- Nine more states have been added to Chicago's COVID-19 travel advisory, even as the U.S. Centers for Disease Control and Prevention is expected to revise its mask guidance, and recommend that some vaccinated people wear masks indoors again.
The Chicago Department of Public Health added Alabama, Alaska, Arizona, Kansas, Mississippi, Oklahoma, Tennessee, Texas, and Wyoming to the travel advisory on Tuesday.
The list now includes 14 states and one territory: Arkansas, Missouri, Florida, Louisiana, Alabama, Virgin Islands, Oklahoma, Mississippi, Nevada, Alaska, Arizona, Texas, Kansas, Tennessee, and Wyoming.
States are added to the list when they surpass 15 coronavirus cases per day per 100,000 residents.
"People who are unvaccinated by far have the highest risk of contracting COVID," said CDPH Commissioner Allison Arwady, M.D. "And the number one way for us to stop the spread of COVID is to get vaccinated and to encourage everyone we know to get their vaccinations. Vaccines are safe and effective."
While the travel advisory does not include any restrictions on visitors, the city said all travelers must still follow masking rules while traveling. Masks are required on planes, buses, trains, and other forms of public transportation traveling into, within, or out of the United States and in U.S. transportation hubs such as airports and stations.
It's the third week in a row Chicago has added states to its travel advisory, after going nearly two months without any states on the list.
Unvaccinated visitors from states and territories on the city's travel advisory are urged to either obtain a negative COVID-19 test result no more than 72 hours before arriving in Chicago, or quarantine for a 10-day period upon arrival.
Anyone who has been fully vaccinated is exempt from the travel advisory.
The announcement comes just hours before the CDC is expected to revise its mask guidance Tuesday afternoon, saying fully vaccinated Americans should wear masks indoors in communities where there is substantial or high transmission, according to a federal official.
It isn't yet clear how substantial or high transmission will be determined by the CDC.
The new guidance comes as a growing number of local and state health officials have already returned to mandating masks indoors, with cases of the virus surging among unvaccinated Americans. Some 63% of U.S. counties currently have "high" or "substantial" spread of the virus, according to the CDC.
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