U.S daily new-case averages take dip

American strains worry virologists

ATLANTA — Average daily new coronavirus cases in the United States dipped below 100,000 in recent days for the first time in months, but experts cautioned Sunday that infections remain high and precautions to slow the pandemic must remain in place.

Additionally, as variants first identified in the United Kingdom and South Africa spread across the country, scientists are finding a number of new variants that originated in the United States.

The seven-day rolling average of new infections was well above 200,000 for much of December and went to roughly 250,000 in January, according to data kept by Johns Hopkins University, as the pandemic came roaring back after it had been tamed in some places over the summer.

That average dropped below 100,000 on Friday for the first time since Nov. 4. It stayed below 100,000 on Saturday.

“We are still at about 100,000 cases a day. We are still at around 1,500 to 3,500 deaths per day. The cases are more than two-and-ahalf-fold times what we saw over the summer,” Dr. Rochelle Walensky, direc

tor of the Centers for Disease Control and Prevention, said on NBC’s “Meet the Press.” “It’s encouraging to see these trends coming down, but they’re coming down from an extraordinarily high place.”

On Saturday, the seven-day rolling average for deaths was around 2,500. That number peaked at more than 3,300 earlier in the winter, according to Johns Hopkins.

The U.S. saw a spike of more than 5,400 deaths reported Friday — nearly half from Ohio, where authorities said earlier in the week that they planned to add deaths to the state’s tally over the course of a few days after discovering as many as 4,000 unreported covid-19 fatalities.

Walensky added that new variants, including one first detected in the United Kingdom that appears to be more transmissible and has already been recorded in more than 30 states, will likely lead to more cases and more deaths.

“All of it is really wraps up into we can’t let our guard down,” she said. “We have to continue wearing masks. We have to continue with our current mitigation measures. And we have to continue getting vaccinated as soon as that vaccine is available to us.”

The U.S. has recorded more than 27.5 million virus cases and more than 484,000 deaths, according to the Johns Hopkins data.

With parents and political leaders eager to have children around the country back in school for in-person learning, it is important that people continue to observe precautions, Walensky said.

“We need to all take responsibility to decrease that community spread, including mask wearing so that we can get our kids and our society back,” she said.

The CDC released guidance on Friday outlining mitigation strategies necessary to reopen schools or to keep them open.

Some teachers have expressed concern about returning to the classroom without having been vaccinated, but the guidelines do not say that’s necessary. Dr. Anthony Fauci said on ABC’s “This Week” that it would be “optimal” if teachers were vaccinated but that other measures laid out in the 24-page document can lessen their risk.

“Practically speaking, when you balance the benefit of getting the children back to school with the fact that the risks are being mitigated, if you follow the recommendations and these new guidelines from the CDC, hopefully, I think that will alleviate the concerns on both sides,” he said.

The comments came as school closures remained in effect throughout the country. Middle schools are set to reopen for in-person learning in New York City later this week, the latest in a series of steps toward getting back to regular schooling there.

Fauci repeated calls for Congress to pass a $1.9 trillion stimulus package including millions of dollars for supplies for schools.

“Schools really do need more resources,” he said. “And that’s the reason why the national relief act that we’re talking about getting passed — we need that.”

HOME-GROWN VARIANTS

In a study posted Sunday, a team of researchers reported seven growing lineages of the coronavirus, spotted in states across the country. All of them have evolved a mutation in the same genetic letter.

“There’s clearly something going on with this mutation,” said Jeremy Kamil, a virologist at Louisiana State University Health Sciences Center Shreveport and a co-author of the new study.

It’s unclear whether it makes the variants more contagious. But because the mutation appears in a gene that influences how the virus enters human cells, the scientists are highly suspicious.

“I think there’s a clear signature of an evolutionary benefit,” Kamil said.

As the coronavirus now branches into new variants, researchers are observing Darwin’s theory of evolution in action, day in and day out.

Kamil found some of the new variants while he was sequencing samples from coronavirus tests in Louisiana. At the end of January, he observed an unfamiliar mutation in a number of samples.

The mutation altered the proteins that stud the surface of the coronavirus. Known as spike proteins, they are folded chains of more than 1,200 molecular building blocks called amino acids. Kamil’s viruses all shared a mutation that changed the 677th amino acid.

Investigating these mutant viruses, Kamil realized they all belonged to the same lineage. The earliest virus in the lineage dated to Dec. 1. In later weeks, it grew more common.

Kamil uploaded the genomes of the viruses to an online database used by scientists across the world. The next morning, he got an email from Daryl Domman of the University of New Mexico, who had found the same variant in that state, with the same mutation. Their samples dated to October.

The scientists wondered whether the lineage they had discovered was the only one to have a 677 mutation. Probing the database, Kamil and his colleagues found six other lineages that independently gained the same mutation on their own.

Scientists are worried because the mutation could plausibly affect how easily the virus gets into human cells.

An infection begins when a coronavirus uses the tip of the spike protein to latch onto the surface of a human cell. It then unleashes harpoon-like arms from the spike’s base, pulling itself to the cell and delivering its genes.

Before the virus can carry out this invasion, however, the spike protein has to bump into a human protein on the surface of the cell. After that contact, the spike becomes free to twist, exposing its harpoon tips.

The 677 mutation alters the spike protein next to the spot where human proteins nick the virus, conceivably making it easier for the spike to be activated.

Jason McLellan, a structural biologist at the University of Texas at Austin who was not involved in the study, called it “an important advance.” But he cautioned that the way that the coronavirus unleashed its harpoons was still fairly mysterious.

Scientists anticipate that coronaviruses will converge on more mutations that give them an advantage — against not only other viruses but also our own immune system. But Vaughn Cooper, an evolutionary biologist at the University of Pittsburgh and a co-author of the new study, said lab experiments alone would not be able to reveal the extent of the threat.

To really understand what the mutations are doing, he said, scientists will need to analyze a much bigger sampling of coronaviruses gathered from across the country. But right now, they can look at only a relatively meager number of genomes collected by a patchwork of state and university labs.

“It’s ridiculous that our country is not coming up with a national strategy for doing surveillance,” Cooper said.