Vox: “An expert explains why vaccinated people should wear masks in some indoor settings. The Centers for Disease Control and Prevention has now done an about-face on its masking guidelines for people vaccinated against Covid-19. Back in May, the agency said that people who are fully vaccinated against Covid-19 could “resume activities without wearing masks or physically distancing.” But the new CDC guidance issued in late July says that vaccinated people should “wear a mask indoors in public if you are in an area of substantial or high transmission.” Even where transmission rates aren’t as high, immunized people with weakened immune systems, and the people they live with, should also consider it. Why the change? The far more contagious delta variant of the virus that causes Covid-19 has rattled health officials. Beyond its rapid spread, the delta variant appears to cause more serious illness. It also seems better able to elude immune protection from vaccines and prior infections. Some breakthrough infections have been reported among vaccinated people, although the majority seem to lead to few, if any, symptoms. And while the vaccination rate has started to pick up again, it’s still far below its peak in April. Tens of millions of Americans remain unvaccinated, and in some regions of the US, less than 30 percent of people are immunized…”