(AP) — Communities across the U.S. are seeing plummeting demand for coronavirus testing. The drop comes at a significant moment in the outbreak: Experts are cautiously optimistic that COVID-19 is receding after killing more than 500,000 Americans. But they are concerned that emerging variants could prolong the epidemic. U.S. testing hit a peak on Jan. 15. Since then, the average number of daily tests has fallen more than 28%. Officials say there are many reasons for the fall. All major virus measures, including new cases, hospitalizations and deaths, are down. Other reasons include harsh winter weather, the end of the holiday travel season, pandemic fatigue and a growing focus on vaccinations.