(CNN) — First, the good news: In 48 states, the averages of new Covid-19 cases have dropped significantly over the past seven days. And every state improved its rate of vaccinations.

Now the bad news: The US is still averaging more than 170,000 new infections a day. And Covid-19 has killed an average of 3,088 people a day over the past week in the US — more deaths each day than the 9/11 attacks.

January is on track to be Covid-19’s deadliest month in the US.

At least 73,259 deaths have been reported this month, according to the most recent data from Johns Hopkins University. That’s more than one death every 30 seconds.

Now it’s a race between vaccines and variants, as health experts say the US must speed up shots before a highly contagious strain of coronavirus spreads more rapidly.

Moderna’s vaccine is expected to work against variants

While all viruses mutate over time, some variants of the novel coronavirus are worrying scientists.

One strain, first identified in the UK, is more transmissible than other variants, scientists say.

The US Centers for Disease Control and Prevention has warned that the country could see “rapid growth” in its spread in early 2021. This B.1.1.7 strain has already been detected in more than 20 US states.

And there’s “a realistic possibility” that B.1.1.7 could be deadlier than other variants, a UK report said.

Another strain, first detected in South Africa, is concerning because scientists have said current Covid-19 vaccines might not be as effective against it.

That strain has been found in more than 20 other countries, though it has not yet been detected in the US.

Two doses of Moderna’s Covid-19 vaccine are “expected to be protective against emerging strains detected to date,” the vaccine maker said.

There was “no significant impact” on the vaccine’s effectiveness against the strain first found in the UK. But there may be somewhat less effectiveness against the strain first detected in South Africa.

“The efficacy might be reduced somewhat, but it may still be very effective,” said David Montefiori, a virologist at Duke University Medical Center. “Hopefully, the vaccine will still be 70-80% effective.”

Moderna said it’s developing a new Covid-19 booster vaccine to protect against the variant first spotted in South Africa. The company plans to first test the vaccine in the lab and in a small Phase 1 clinical trial in the US.

Johnson & Johnson’s coronavirus vaccine candidate is being tested in Brazil, South Africa and the United States and results might provide insight into how well it works against emerging new variants, one of its developers told CNN Senior Medical Correspondent Dr. Sanjay Gupta on the Coronavirus Fact vs Fiction podcast.

The company has said that it could share its Phase 3 trial data as early as this week.

“It’ll give us insights not only into whether or not this vaccine candidate is effective, but it’ll also give us insights into whether or not the variants that are circulating in South Africa might be a problem for vaccines,” said Dr. Dan Barouch, who is the director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center and Harvard Medical School.

100 million doses in 100 days is ‘a floor. It’s not a ceiling’

President Joe Biden has promised 100 million shots will be given in his first 100 days in office — a goal that has been criticized by some as too modest.

“We need to do better than a million shots per day,” said Dr. Jonathan Reiner, professor of medicine at George Washington University.

“We need to do better. We need to vaccinate about 2 million people a day. That should be the goal.”

But Dr. Vivek Murthy, Biden’s nominee for US surgeon general, said the goal of a million doses a day is “a floor. It’s not a ceiling.”

“We’ve got to vaccinate as many Americans as possible,” Murthy told ABC’s “This Week” on Sunday.

“And that’s going to take a lot of work — work dispelling misinformation, working on the supply, increasing distribution channels,” Murthy said. “And that’s some of what the vaccine plan that (Biden) announced over the last week is intended to achieve.”

Both the Pfizer/BioNTech and the Moderna vaccines require a second dose three to four weeks after the first. And most of the shots given now are first doses, Reiner said.

“As we go forward, more and more shots every day will be the second vaccination,” he said.

“So the number of new vaccinations is going to start to drop until we get to a point in the not-too-distant future where every day the shots that are given are 50% follow-up and 50% new vaccinations.”

According to the CDC’s website, 18.5 million people have received a first dose and 3.2 million have been fully inoculated with a second.

How to stop the spread of variants

Fewer than 1% of all Americans have received both doses of a Covid-19 vaccine, according to CDC data.

“We’re looking at probably middle of the summer, end of the summer before the average, healthy, young American has access to vaccination,” said infectious disease expert Dr. Celine Gounder.

And with the B.1.1.7 variant spreading in the US, it’s up the public to take personal responsibility to stop it’s spread.

“The best way to prevent the emergence of new variants is to do all of the things we’ve been talking about for months,” Gounder said.

That includes keeping your distance from others and wearing a mask anytime you might be near someone who doesn’t live with you.

“The more you let the virus spread, the more it mutates, the more variants you’ll have,” Gounder said.

Some people have started wearing two masks at once. When asked whether that would help, Dr. Anthony Fauci told NBC’s “Today” show that it probably would.

“I mean, this is a physical covering to prevent droplets and virus to get in,” said Fauci, the director of the National Institute of Allergy and Infectious Diseases.

“So if you have a physical covering with one layer, you put another layer on, it just makes common sense that it likely would be more effective. And that’s the reason why you see people either double masking or doing a version of an N95.”

N95 respirators have been in high demand and short supply throughout the pandemic. The Biden administration has committed to invoking the Defense Production Act more often to boost the manufacturing of N95 masks and other critical supplies.

Send us your questions for President Biden’s Covid-19 team

California lifts regional stay-at-home orders

In a sign of progress, one of hardest hit states is lifting regional stay-at-home orders Monday.

“We are turning a critical corner,” said Dr. Tomás Aragón, director of the California Department of Public Health.

The orders applied to Southern California, the San Joaquin Valley and Bay Area regions, affecting more than 90% of the state’s population.

The mandate was triggered when ICU capacity in a region fell below 15%. The four-week ICU capacity projections for these regions are now above 15%, the state reported.

“Californians heard the urgent message to stay home as much as possible and accepted that challenge to slow the surge and save lives,” Aragón said.

“Together, we changed our activities knowing our short-term sacrifices would lead to longer-term gains,” he said.

“Covid-19 is still here and still deadly, so our work is not over, but it’s important to recognize our collective actions saved lives.”

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