The pace of new coronavirus infections continued to plummet over the past week, despite upticks in the already hard-hit Dakotas.

Why it matters: This sustained drop in new cases is unambiguously good news. If the U.S. can keep it going, this progress will save lives, make it easier to safely reopen schools and businesses, and help minimize the threat posed by more contagious variants of COVID-19.

By the numbers: The U.S. averaged roughly 82,000 new cases per day over the past week — a 24% drop from the week before. Cases have been falling at about that pace for weeks.

• New cases declined in 44 states. They increased in both North and South Dakota. Nebraska also reported an increase in new daily cases over the past week, though it was driven largely by an unusual one-day spike that may be a reporting quirk.
• This is the first time since early November that the U.S. has averaged fewer than 100,000 cases per day.
• Hospitalizations were down by 25%, and average daily deaths fell by about 5%. On average, roughly 2,900 Americans are now dying each day from their coronavirus infections.

Between the lines: There’s no easy, comprehensive explanation for this sudden improvement.

• “I think the most likely explanation is a mix of policy and individual-level behavior change, as people react to what they see in the news and in their communities, but helped along by acquired immunity due to widespread infection plus targeted vaccination,” tweeted Natalie Dean, an infectious-disease expert at the University of Florida.

What’s next: The bitter cold and ongoing power outages in Texas could force people to huddle together indoors for their own safety, which in turn could lead to new coronavirus outbreaks.

• COVID-19 variants — first and foremost, a British variant that’s more contagious than the strain we’re used to, and potentially also more deadly — continue to gain ground, which also threatens to drive cases back up.
• But we’re managing to get cases way, way down as those variants spread now, and keeping that trajectory going while ramping up vaccinations is the best way to guard against another wave of infections, hospitalizations and deaths.

Each week, Axios tracks the change in new infections in each state. We use a seven-day average to minimize the effects of day-to-day discrepancies in states’ reporting.