The Centers for Disease Control and Prevention (CDC) is resisting changing its guidance on masking and other measures meant to mitigate the risk of COVID-19 despite cases, hospitalizations, and deaths dropping across the United States in recent weeks. The key factor is the agency’s system for ranking community transmission of the virus that causes COVID-19. That ranks counties as having “substantial” or “high” transmission if there are 50 or more new cases per 100,000 people in the past 7 days. The ranking system has not been changed since the spring of 2020, even as the number of tests performed has soared. As the CDC considers whether to change guidance, “we recognize the importance of not just cases, which continue to result in substantial or hide community transmission and over 97 percent of our counties in the country, but critically, medically severe disease that leads to hospitalizations,” CDC Director Dr. Rochelle Walensky …