The Centers for Disease Control and Prevention issued new guidance recommending indoor mask use in counties with high rates of transmission – even for vaccinated individuals.  The announcement came as new studies have shown breakthrough Covid infections in vaccinated individuals have just as much viral load as infected people who are unvaccinated. CDC COVID tracker by State and County at https://covid.cdc.gov/covid-data-tracker/ As of Feb. 4th, 99.8 percent of U.S. counties, including Puerto Rico’s municipalities, fall under the mask guidance. This map showing the CDC’s recommendations will be updated daily.  The CDC also issued guidance that children wear masks in classrooms when the school year begins.  The delta variant, which officials have said is more contagious than the original coronavirus strain, is contributing to a fourth wave of infections and hospitalizations.  An area’s level of virus transmissibility depends on two factors: the average number of cases relative to a county’s population and the Covid test positivity rate. The CDC recommends people wear masks indoors in counties that either average 50 or more cases per 100,000 residents or have a test positivity rate equal to or greater than 8 percent.