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Covid-19 numbers are improving, but infections could grow exponentially with Super Bowl gatherings

(CNN) Covid-19 cases and hospitalizations are decreasing across much of the United States, but health experts warned that could change if fans gathered Sunday to watch the Super Bowl with people from outside their households.

"When people get together in private residences in close proximity, that is one of the single most effective ways to spread this disease," Kentucky Public Health Commissioner Dr. Steven Stack said. "We can't afford to have the disease spread now, with these mutations and these variants."

New York Gov. Andrew Cuomo said, "while the instinct may be to celebrate together, we cannot get cocky."

"We must continue doing the things we know are effective at taming the virus: wear a mask, adhere to social distancing, and avoid gatherings," he said. "We can beat this thing, but we must stay smart."

That's especially true after a new study found the highly contagious B.1.1.7 strain, first detected in the United Kingdom, is now spreading rapidly in the US.

While the B.1.1.7 strain still makes up a relatively small portion of known US cases, it's doubling about every 10 days, researchers said.

US labs are still sequencing only a small portion of coronavirus samples, the researchers said, so it's not clear what variants are circulating in the country.

At least 699 cases of the coronavirus variants first identified in the UK, South Africa and Brazil had been reported in the US as of Sunday, according to data from the US Centers for Disease Control and Prevention. The vast majority of them, 690, were the B.1.1.7 variant, which has so far been identified in 33 states.

Last month, the CDC projected the B.1.1.7 variant could become the predominant strain in the US by March. It estimates the virus is about 50% more transmissible.

Without "decisive and immediate public health action," the researchers warned, more transmissible variants "will likely have devastating consequences to COVID-19 mortality and morbidity in the U.S. in a few months."

Why some Covid-19 numbers are getting better

After an abysmal start to winter -- marred by record-breaking new cases, hospitalizations and deaths -- new cases and hospitalization figures are improving.

The US just marked its eighth consecutive day with less than 100,000 people hospitalized for Covid-19, according to the COVID Tracking Project.

And the seven-day average of new cases has dropped from 220,000 on January 6 to 120,000 on Saturday.

Such good news is probably the result of holiday-related infections tapering off, as well as Americans doing a better job with safety precautions, according to Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

"That's what I think is going on: a combination of the natural peaking, as well as people doubling down on the public health measures," Fauci told MSNBC on Friday.

But daily Covid-19 deaths are still high. For weeks, the US has reported a daily average of more than 3,000 Covid-19 deaths, according to data from Johns Hopkins University. The average daily death toll exceeds the number of lives lost in the 9/11 attacks.

Some say safety measures, not vaccinations, are a must for school openings

The CDC is expected to release guidelines this week on how to open schools safely during the pandemic.

On Sunday, Fauci and Dr. Scott Gottlieb said while it's important to vaccinate teachers, it's not a prerequisite to open schools.

Mitigation measures, however, are a must.

Getting K-8 schools open in 100 days is a priority of President Joe Biden's administration, Fauci told NBC's "Meet the Press" Sunday, but "they're going to need some help" so schools can have "the capability with masks, with the ability to get better ventilation, all the things you want to do."

"It would be great to get all the teachers vaccinated as quickly as we possibly can," Fauci said.

Gottlieb, a former commissioner of the US Food and Drug Administration, told CBS' "Face the Nation" that when it comes to opening schools, "I think the prerequisite is putting in place mitigation steps in the schools."

He noted that research showed that when people wore masks, stayed distanced and took precautions, "there's very little transmission within the classroom. The schools are not a vector of transmission."

Gottlieb said while it would be good to vaccinate teachers quickly, "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."

Fauci: There's probably not enough time for certain 1-dose studies

The two vaccines currently administered in the US -- from Pfizer/BioNTech and Moderna -- both require two doses, spaced three or four weeks apart.

But supply is still limited. And health experts have debated whether the US should give first doses to as many people as possible now, at the risk of delaying second doses for some people.

Fauci said that there may not be enough time to study how much protection is provided by one dose or how long that protection might last.

"By that time, we will already be in the arena of having enough vaccines to go around anyway," Fauci told NBC's "Meet the Press" Sunday.

"From a theoretical standpoint, it would be nice to know if you just get one dose, how long the durability lasts and what (is) the level of effect," Fauci said. "So it would be great to have the study, but I don't think we could do it in time."

Fauci said he believes "you can get as many people... their first dose at the same time as adhering within reason to the timetable of the second dose."

Meanwhile, a third vaccine -- which requires only one dose -- might become available to the public in the coming weeks.

Johnson & Johnson officially asked the US Food and Drug Administration for an emergency use authorization of its one-dose Covid-19 vaccine Thursday. A decision could be made by the end of this month.

AstraZeneca's vaccine will be discussed

Early data suggests two doses of another vaccine, this one from Oxford/AstraZeneca, provide "minimal protection" against mild and moderate Covid-19 from the B.1.351 variant first identified in South Africa, the University of Oxford said Sunday.

Viral neutralization against the B.1.351 variant was "substantially reduced" when compared to the earlier coronavirus strain, according to a news release Sunday from the University of Oxford.

The study, which has not been released, included about 2,000 volunteers who were an average of 31 years old. About half received the vaccine and half received a placebo.

The vaccine's efficacy against severe Covid-19, hospitalization and death were not assessed.

After the Financial Times reported on the study Saturday, AstraZeneca said it believes the vaccine could protect against severe disease. The company said it has started to adapt the vaccine against the variant "so that it is ready for Autumn delivery should it be needed."

The World Health Organization's independent panel on vaccines will meet Monday to discuss the AstraZeneca vaccine and studies assessing how effective it is against the the B.1.351 strain, WHO technical lead for Covid-19 Maria Van Kerkhove told CBS's "Face the Nation" on Sunday.

A spokesperson for AstraZeneca told CNN on Saturday that a small trial found the company's Covid-19 vaccine provides limited protection against mild disease in cases caused by the B.1.351 variant. The study has not yet been peer-reviewed.

There are "some preliminary studies suggesting reduced efficacy," Van Kerkhove told CBS. "But again, those studies aren't fully published yet."

Where the US stands on vaccines

Just over 31.5 million people have received at least their first dose of a Covid-19 vaccine, according to data published Sunday by the CDC. More than 9 million people have been fully vaccinated with two doses.

In some parts of the country, officials are working to improve vaccine accessibility to underserved and vulnerable communities.

In the Houston area, local officials say hospitals that are open to uninsured people are getting a smaller percentage of doses than private hospitals.

"You can have the best healthcare in the world, but if people can't access it, it's like you don't have it at all," Houston Mayor Sylvester Turner said.

"If you want to address the disparity, you've got to send the doses to the venues that are reaching those regions."

In the Northeast, some people won't get vaccinated Sunday because of another challenge: weather.

A massive winter storm that hit the region last week disrupted vaccine efforts in several states. On Saturday, Cuomo said some vaccination sites in New York would suspend operations Sunday.

"New Yorkers with testing or vaccination appointments at these sites will receive notification of these suspensions via text message and telephone," the governor's office said. Appointments will be rescheduled for later in the week.

'The perfect environment' for viral spread

While many parts of the country have loosened Covid-19 rules amid declines in their numbers, others are standing firm on their mandates.

In New Orleans, several bars were shut down after failing to comply with Covid-19 restrictions, officials said Saturday.

Los Angeles County, which suffered a crippling Covid-19 surge crisis, recently announced restaurants could reopen for outdoor dining -- with restrictions. But Public Health Director Barbara Ferrer said the county is still "a ways away from indoor dining."

"The virus is really easily transmitted when you don't have a face covering on," she said. "So when you're indoors to eat or drink and you have to take your face covering off, that's like the perfect environment for this virus to get transmitted."

CNN's Jamie Gumbrecht, Naomi Thomas, Elizabeth Joseph, Andy Rose, Kay Jones, Hollie Silverman, Lauren Mascarenhas, Melissa Alonso and Rebekah Riess contributed to this report.