No, you’re not crazy. Yes, the CDC’s mask guidelines are confusing — should you wear a mask indoors even if you’re vaccinated?

Wear a mask. Don’t wear a mask. Make one. Buy one. Wear it outdoors. Wear it indoors.

Confused? You’re not alone.

So what’s the deal with the CDC’s new guidance? In an effort to help combat the highly contagious delta variant, the U.S. Centers for Disease Control and Prevention said Tuesday that people in areas with “substantial” or “high” rates of COVID-19 should go back to wearing masks in public indoor spaces.

“The delta variant is showing us every day its willingness to outsmart us,” Dr. Rochelle Walensky, director of the CDC,...