The death rate hasn't plummeted. It has gone down yes, because there has been a significant increase of infection. When the number of infected go up, and fatalities steadily climb, the fatality rate can still slump. Since it takes anywhere from two-three weeks; it's expected that in about two weeks the fatality rate will climb back up.
Perhaps it won't, perhaps it may stay steady. I'm only explaining why increasing the numbers of infected is causing the fatality rate to go down. We're still seeing a steady average in deaths, however.