• Dr. Anthony Fauci on Sunday warned Americans to steel themselves against a sense of Covid-19 complacency even as coronavirus infections plummet and some scientists predict that herd immunity is just around the corner.
• "The slope that's coming down is really terrific — it's very steep, and it's coming down very, very quickly. But we are still at a level that's very high," Fauci, a top pandemic advisor to President Joe Biden, said on NBC's "Meet the Press."
• Fauci said he didn't want people to think that just because the slope of infections was in sharp decline that "we're out of the woods now."

Dr. Anthony Fauci on Sunday warned Americans to steel themselves against a sense of Covid-19 complacency even as coronavirus infections plummet and some scientists predict that herd immunity is just around the corner.

"The slope that's coming down is really terrific — it's very steep, and it's coming down very, very quickly. But we are still at a level that's very high," Fauci, a top pandemic advisor to President Joe Biden, said on NBC's "Meet the Press."

Fauci said he didn't want people to think that just because the slope of infections was in sharp decline that "we're out of the woods now."

"We're not. Because the baseline of daily infections is still very, very high," Fauci said. "It's not the 300,000 to 400,000 that we had some time ago, but we want to get that baseline really, really, really low before we start thinking that we are out of the woods."

The pandemic that first gripped the nation at the start of last year has entered a new phase, as the pace of vaccinations picks up and the number of new infections decreases even as the U.S. is about to hit the grim milestone of 500,000 Covid-19-related deaths.

The 7-day moving average of new infections was 71,717 on Saturday, according to a CNBC analysis of data from Johns Hopkins University, less than half of the 146,034 daily new infections reported at the start of the month, also a 7-day average.

More than 497,000 people in the U.S. have died of the disease as of Sunday.

Fauci's comments to host Chuck Todd came in response to a Thursday opinion article published in The Wall Street Journal by Dr. Martin Makary, a surgeon at Johns Hopkins University, which predicted the country will reach herd immunity in April.

Makary wrote that his prediction was based on data and science as well as anecdotal evidence. He said that, in private, some medical experts agreed with his outside-the-consensus view, but had warned him against discussing it lest he inadvertently encourage members of the public to become complacent, fail to take precautions or refuse to receive the vaccine.

"At the current trajectory, I expect Covid will be mostly gone by April, allowing Americans to resume normal life," Makary wrote, saying current estimates of natural immunity were probably low.

Fauci said that he was "not so sure" that the recent decline in infections could be attributed to herd immunity, or the phenomenon in which a critical number of individuals become resistant to the virus as a result of prior exposure or vaccination.

"Certainly, the number of people that have been infected are contributing to that. Also, some contribution with vaccines, not a lot," Fauci said. "I don't think we've vaccinated enough people yet to get the herd immunity. I think you're seeing the natural peaking and coming down."

Dr. Scott Gottlieb, the former chief of the Food and Drug Administration, weighed in as well on Sunday, saying in an interview on CBS News' "Face the Nation" that he expected the current decline in cases to continue.

Gottlieb said that the rate of infections can be slowed significantly if just 40% of the population has some form of immunity, a lower figure than the 75% that Fauci has estimated to be the level for herd immunity.

In some parts of the country, Gottlieb added, "that's what we have right now."

"We should be optimistic, in my view. I think we are going to continue to see infection rates declining into the spring and the summer," he said.

The debate over the state and momentum of the virus comes a year into the extended lock downs and other preventive measures that have shuttered much of the economy, inflicted mental health trauma on an as-yet-untold number, and forced families apart.

Biden has said that achieving herd immunity by the end of the coming summer could be a difficult task, forcing parents to grapple with the idea of starting another school-year in pandemic conditions.

Even if the country significantly contains the virus, it is possible that some measures designed to protect against its spread continue. Fauci said on CNN on Sunday that Americans may be wearing masks to prevent the spread of Covid-19 next year, even as the country reaches a degree of normality.

"It's possible that that's the case," Fauci said of wearing masks in 2022. "It depends on the level of dynamics of virus that's in the community. If you see the level coming down really, really very low, I want it to keep coming down to a baseline that's so low that...there's a minimal, minimal threat you'll be exposed to someone who's infected."

Biden's cautious approach is a reversal from the abundant and at times reckless optimism offered by his predecessor, former President Donald Trump. The Biden administration's measured remarks have inspired criticism from the opposite direction, with some saying the administration sets goals that are too low in the face of encouraging data.

The uptick in the number of individuals receiving vaccinations has spurred limited optimism. About 1.7 millions vaccines are administered each day, up from the White House goal of 1.5 million per day. Public health experts have said that rate could double by the end of the month, if supply persists.

Despite those optimistic projections, concerns are still high about a number of new coronavirus mutations, some of which have been shown to be more transmissible than the dominant strain in the U.S. It is possible that mutant strains could prove resistant to the vaccines that have been approved by regulators, though experts have largely said they expect the current vaccines to work.

One particularly worrying strain, first identified in the U.K., is doubling its presence in the U.S. every 10 days, according to a study published earlier this month.

While the study found that the strain was circulating at low absolute levels, it supported modeling produced by the Centers for Disease Control and Prevention that predicted the strain, known as B.1.1.7., could be the dominant strain in the U.S. next month.

Dr. Michael Osterholm, a former advisor to Biden's transition team, said on Jan. 31 that B.1.1.7 was likely to lead to a surge in the "next six to 14 weeks."

"And, if we see that happen, which my 45 years in the trenches tell me we will, we are going to see something like we have not seen yet in this country," Osterholm warned.

The CDC has identified three mutant strains in the U.S. that "in particular have concerned global public health and healthcare leaders to date," including B.1.1.7 and variations first identified in South Africa and Japan. The variant identified in Japan was found in travelers from Brazil.

Gottlieb said that the variants did pose "some risk" but that there was already "enough protective immunity that we are likely to see these [positive] trends continue."

The variants, he said, are "not going to be enough to reverse these trends at this point."

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