gupta
Why do vaccinated people need to mask? See Gupta's answer
02:54 - Source: CNN
CNN  — 

Health guidance issued Tuesday recommends that fully vaccinated people wear masks indoors if they’re in areas with “substantial” or “high” transmission of Covid-19. But what do “substantial” and “high” actually mean?

The two terms are part of the US Centers for Disease Control and Prevention’s four-tiered system that measures the level of community transmission in each county: low, moderate, substantial and high. On the CDC’s website, you can run a search by state or county and click around the color-coded map to see how active the virus is where you live.

A county’s level of transmission is based on just two metrics: new Covid-19 cases per 100,000 people and the positivity rate, both measured over the last seven days. The basic idea is that these show how much virus is spreading around us, CNN Medical Analyst Dr. Leana Wen said.

“The level of coronavirus transmission is an important determinant of how much risk you’re in, if you’re vaccinated or unvaccinated,” she said.