Daily cases of new coronavirus plunged more than 100,000 on Thursday after falling below the threshold for the first time since the fall earlier in the week.
The overall trend in recent weeks is still positive as cases and hospitalizations are off their highs in January.
But the 103,000 cases on Thursday, as counted by the COVID Tracking Project, are a reminder that the spread of the virus is still at very high levels, and more contagious variants threaten to start a new boom.
Business declined 23 percent from last week and 57 percent from its peak in January. Hospitalizations are 42 percent lower than their high watermarks, according to the COVID Tracking Project.
But the toll of the virus remains heavy, with about 3,000 people dying every day. Deaths are a backlog, so the drop in cases will take longer to appear there.
And the threat of more contagious variants, especially one first identified in the UK, known as B.1.1.7, threatens to undo downward trends.
A match has in fact been started between the new variants and vaccinations. Experts say the faster people can be vaccinated, the more they will do to prevent a new peak of the variant from occurring.
Other precautions remain important, including wearing a mask, avoiding indoor gatherings, and maintaining distance from others.
The Centers for Disease Control & Prevention stressed on Thursday that it is important to wear a mask that fits well, saying that wearing a cloth mask over a medical procedure can significantly reduce transmission.