Positive trends in pandemic statistics in the United States are easy to distrust. After all, the country went through two false dawns last year, in the late spring and then again in the late summer, when declines in case reports prefaced even darker days. Each time, the apparent good news prompted relaxations and reopenings that helped bring on the next wave.So it is no surprise that public health experts are wary about the latest flattening in the curve of the pandemic, from the steep decline in cases seen in late January and February to something like a plateau or slight decline more recently. With more contagious virus variants becoming prevalent, they fear the good news could be ending and a fourth wave might be building.That said, there are positive signs:Daily death reports, which stayed stubbornly high long after the post-holidays surge, have finally come down sharply, to levels not seen since mid-November. As of Monday, the nation had averaged 1,051 newly reported Covid deaths a day over the past week; the average had hovered around 3,000 for weeks over the winter.Some recent hot spots have made major progress — notably Los Angeles, whose mayor, Eric Garcetti, said on CBS on Sunday that he had “not felt this optimism in 12 months.” The city and surrounding county, where cases in some areas leapt 450 percent over the holidays and hospitals became so swamped that some turned away ambulances, now has a test positivity rate of about 1.9 percent, and in an important shift, new case reports have fallen among people experiencing homelessness.Vaccinations are becoming more accessible by the week, as states receive more doses and open up eligibility, in some cases to include all adult residents. The number of doses administered nationwide each day is rising, and the country surpassed President Biden’s initial goal to have administered 100 million shots on March 19, almost six weeks ahead of schedule.The question now is which will prevail: the positive effects of trends like these or the negative effects of looser behavior and the evolution of the virus into more dangerous forms?It’s still “a race between vaccinations and variants,” Dr. Ashish Jha, dean of the Brown University School of Public Health, said on Twitter. Like other experts, he cautioned: “Opening up too fast helps the variants.”Listen to ‘The Daily’: A Food Critic Loses Her Sense of SmellA Times restaurant critic is on a quest to regain a crucial ability after Covid-19.