While a recent dip in COVID-19 infections may seem encouraging, experts warn now is not the time for Americans to let their guard down.

That's largely because of new variants circulating in the U.S., putting the country once again in the "eye of the hurricane," according to one expert.

"I've been on Zoom calls for the last two weeks about how we're going to manage this," Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine, told CNN Sunday. "The big wall is about to hit us again and these are the new variants."

Nearly 700 cases of COVID-19 variants first spotted in the U.K., South Africa and Brazil have been reported in the U.S. so far, according to data updated by the Centers for Disease Control and Prevention.

The vast majority of those cases are the B.1.1.7 strain, which was first detected in the U.K. and has now been spotted in at least 33 states. Experts say the highly contagious variant will likely soon become dominant in the U.S., and a new study found significant community transmission may already be occurring.

"This could be really, very dire for our country as we head into the spring," Hotez said of the variants. "Now, we're in a race. We're in a race to see how quickly we can vaccinate the American people."

On Sunday, the U.S. surpassed 27 million reported infections, according to Johns Hopkins University data. More than 31 million Americans have so far received at least their first dose of either the Pfizer or Moderna vaccine, according to CDC data, as officials work to ramp up vaccinations across the country. More than 9 million people have so far received both doses of a vaccine, according to the data.

And a third vaccine could be on its way to the U.S. market soon: Johnson & Johnson asked the Food and Drug Administration for an emergency use authorization of its vaccine last week.

WHAT WE KNOW ABOUT VARIANTS AND VACCINES

But COVID-19 variants have also complicated things for some vaccines. Here's what we do know.

Health experts continue to encourage Americans to get vaccinated as soon as they can. Research published last month offered reassuring evidence that people who are vaccinated against the virus will also likely be protected against emerging new variants.

Moderna previously said two doses of its vaccine are expected to protect against variants first detected in the U.K. and South Africa, but added it was planning to test booster shots out of an abundance of caution. Pfizer also said last month it was "laying the groundwork" to create vaccine boosters if a variant "shows evidence of escaping immunity by our vaccine."

Due to uncertainty over the effect the Oxford/AstraZeneca vaccine has on hospitalizations, Abdool Karim, head of South Africa's COVID-19 advisory board, said the country is pausing the widespread rollout of the vaccine in favour of a "stepped approach," giving shots to 100,000 people to study its impact on severe disease and hospitalization.

"If we find that the hospitalization rates are below the threshold that we are looking at, then we can be confident that the vaccine is efficacious and maintains its efficacy against hospitalization," Karim told CNN's Becky Anderson. "And if so we can then proceed to continuing the rollout."

Early data released Sunday suggested two doses of the vaccine provided only "minimal protection" against mild and moderate COVID-19 from the variant. The vaccine's efficacy against severe COVID-19, hospitalization and death were not assessed.

An AstraZeneca spokesperson said in a statement, "We do believe our vaccine will still protect against severe disease" from the variant and added that "neutralizing antibody activity is equivalent to other COVID-19 vaccines that have demonstrated activity against more severe disease, particularly when the dosing interval is optimized to 8-12 weeks."

CONCERNS OVER SUPER BOWL PARTIES

Officials have continued to remind Americans it's not just vaccines that will play a role in helping slow the pandemic in the coming months. It's also the public health measures that have proved effective in curbing the spread of the virus: masks, social distancing, avoiding gatherings and regular hand washing.

But some opted to leave those suggestions at home over the weekend ahead of and following the Super Bowl. Images emerged out of Tampa, Florida, of crowded streets and venues as well as events with mask-less attendees and parties hosted by celebrities.

"I'm extremely concerned," Dr. Melissa Clarke, a member of the District of Columbia's advisory committee on vaccine distribution, told CNN Sunday. "Now, we're facing the issues not just of Super Bowl parties, but the fact that it's going to be spring soon and spring fever is going to set in and people that have been caged up in their homes all winter are going to want to get out."

"I would caution everybody: please remember to continue to practice those behaviours and not get COVID fatigue," Clarke added. "Continue to mask, continue to distance, continue to avoid crowds."

WHAT IT WILL TAKE TO REOPEN SCHOOLS

Mitigation measures will play an especially key role in helping schools safely reopen, two officials said Sunday, as the CDC is expected to soon release guidelines on how schools can open during the pandemic.

Schools' safe reopening is "a simple question but with a complicated answer, because it really depends on the level of infection in the community," Dr. Anthony Fauci told NBC on Sunday.

For one, communities should work to get teachers quickly vaccinated, Fauci said. And there should also be a focus on getting schools what they need to reopen, including masks and proper ventilation, among other measures.

Dr. Scott Gottlieb, former FDA commissioner, told CBS that when it comes to reopening schools, "the prerequisite is putting in place mitigation steps in the schools."

He noted that when people wore masks and stayed socially distant, there was "very little transmission within the classroom."

And while it would be good to prioritize teachers for vaccines, he said, "I don't think it's necessarily a prerequisite. I think schools have demonstrated that they can open safely if they've taken precautions in the classroom."

Their recommendation comes amid an ongoing struggle in many parts of the country on how to safely resume classes.

About 62,000 New York City middle school students who opted for in-person learning will be returning to the classroom February 25, according Department of Education Deputy Press Secretary Danielle Filson. Teachers and staff will return the day before to prepare.

Those teachers returning to the classroom are being prioritized for vaccine access at city hubs from February 12 to 21 and over midwinter recess, NYC Department of Education Chancellor Richard Carranza said.

Announcements on tentative agreements paving a path back to in-person instruction came out of San Francisco and Chicago Sunday, where officials have been at odds with school employees on what the best approach for a return is.