(CNN)With every Covid-19 vaccination, the United States inches closer to defeating the pandemic that has killed over half a million Americans and left countless more with long-term complications.
But major challenges stand in the way. Some Americans are ditching personal responsibility and forgoing masks, even though the highly contagious B.1.1.7 variant has spread to at least 46 states and Washington, DC.
"That strain is increasing exponentially. It's spiking up," said Dr. Celine Gounder, an infectious diseases specialist and epidemiologist. "So we are probably right now on a tipping point of another surge."
Research shows that in the US, the B.1.1.7 variant is 59% to 74% more transmissible than the original novel coronavirus.
And the current rate of vaccinations might not be fast enough to fend off a major B.1.1.7 surge in the coming weeks.
"At 2.9 to 3 million doses of vaccine a day over the next six to 14 weeks, when this surge is likely to happen, is not going to really take care of the problem at all," Michael Osterholm, director of the University of Minnesota's Center for Infectious Disease Research and Policy, told NBC's "Meet the Press" on Sunday.
Osterholm said the US should take a lesson from Europe, which has struggled with the B.1.1.7 strain after it was first detected in the United Kingdom.
Just one month ago, B.1.1.7 made up around 4% of coronavirus cases in the US, among those that have undergone genomic sequencing. "Today, it's up to 30 to 40%," Osterholm told NBC on Sunday. "And what we've seen in Europe, when we hit that 50% mark, you'll see cases surge."
After weeks of declines, new Covid-19 cases have basically plateaued at high levels each day.
On average, more than 60,000 Americans were infected every day over the past week, according to Johns Hopkins University. That's slightly less than the peak of the summer surge, when 67,030 infections were reported on July 20.
The US shouldn't loosen coronavirus restrictions until daily new cases fall below 10,000, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease.
He said it's "inexplicable" that some states are rolling back safety measures such as mask mandates, when masks are needed to help fend off B.1.1.7 and other concerning variants.
"I understand the need to want to get back to normality, but you're only going to set yourself back if you just completely push aside the public health guidelines -- particularly when we're dealing with anywhere from 55 (thousand) to 70,000 infections per day in the United States," Fauci said.
Despite health leaders' warnings, several state leaders announced they were easing Covid-19 restrictions.
Texas Gov. Greg Abbott announced last week he was lifting the statewide mask mandate and doing away with any capacity limits on businesses starting this Wednesday
Mississippi Gov. Tate Reeves also said he was lifting all county mask mandates and would allow businesses to operate at full capacity without any state-imposed rules.