LOS ANGELES - Over the last few weeks, the number of coronavirus cases and deaths have continued to decline amid increased efforts to get the American population vaccinated. But the director of the U.S. Centers for Disease Control and Prevention stressed Friday that the trajectory of the pandemic is still concerning, as emerging variants of COVID-19 could be stalling progress in beating the virus back.
"The latest data suggest that these declines may be stalling, potentially leveling off at still a very high number," Rochelle Walensky, the director of the CDC, said during a White House coronavirus task force briefing Friday.
"We, at the CDC, consider this a very concerning shift in the trajectory," Walensky continued. "In fact, cases have been increasing for the past three days, compared to the prior week."
Walensky noted that deaths tend to fluctuate more than cases and hospital admissions, but said that the seven-day average of daily new cases is now higher than the seven-day average earlier in the week.
"We are watching these concerning data very closely to see where they will go over the next few days," Walensky said. "But it’s important to know where we are in the pandemic. Things are tenuous. Now is not the time to relax restrictions."
Although the United States has been experiencing large declines in cases and admissions over the last six weeks, Walensky said the decreases follow the highest peak yet in the pandemic.
As of Friday, there were 77,291 new cases reported of COVID-19 in the U.S. and over 28.4 million cumulatively, according to data from Johns Hopkins University. The virus has claimed the lives of more than 508,000 Americans.
"So, I want to be clear: Cases, hospital admissions and deaths all remain very high, and the recent shift in the pandemic must be taken extremely seriously," Walensky said.
According to Walensky, the CDC has been "sounding the alarm" on new variants in the U.S., predicting that other variants — including the B.1.1.7 variant, which is twice as transmissible as the original strain of the coronavirus — will become the dominant variant of the virus circulating in the country by mid-March.
B.1.1.7 now accounts for approximately 10 percent of cases in the U.S, and prevalence is even higher in certain parts of the country, Walensky noted.
"We may be done with the virus, but clearly the virus is not done with us," Walensky said.
New variants detected in California and New York
New variants of the coronavirus have been detected in both California and New York and are spreading rapidly, according to researchers — and this is adding to concerns that emerging and possibly more contagious strains could hinder the recent downward trend of cases in the country.
One variant in New York City, called B.1.526, was first detected in late November 2020. By mid-February, it appeared in roughly 25% of the coronavirus genomes sequenced and entered into a database shared by researchers.
Meanwhile, a new coronavirus variant, called CAL.20C, has also been detected in Southern California amid a surge in local infections and has been spreading rapidly, according to research published Feb. 11 in the JAMA medical journal.
This variant was first detected in July 2020 in 1 out of 1,247 samples from Los Angeles County. Researchers said it wasn’t detected in Southern California again until October. Since then, the prevalence of CAL.20C has increased throughout the state — accounting for 35% of all samples collected in late January, and 44% of all samples collected from Southern California counties, specifically.
Primary variants emerged in fall 2020
Some of the primary variants emerged in the fall of 2020, complicating global efforts to combat the coronavirus and contributing to rapid spread in major metropolitan areas, including London and Los Angeles.
There are many varied coronavirus strains circulating around the world, but health experts are primarily concerned with the emergence of three — the U.K., South Africa and Brazil variants — which also appear more contagious, experts say.
In the United Kingdom, a variant of SARS-CoV-2 emerged with an unusually large number of mutations.
Meanwhile, in South Africa, another variant emerged independently of B.1.1.7.
On Dec. 18, South Africa announced the detection of the mutation in three provinces: Eastern Cape, Western Cape and KwaZulu-Natal provinces.
According to the CDC, the South Africa variant shares some mutations with B.1.1.7, the U.K variant.
In Brazil, a variant of SARS-CoV-2 (known as P.1) emerged and was identified in four travelers from Brazil, who were tested during routine screening at Haneda airport outside Tokyo, Japan.
According to the CDC, the Brazil variant has "17 unique mutations, including three in the receptor binding domain of the spike protein.
Viruses continue to mutate
As a virus infects people, it can mutate as it makes copies of itself. Some mutations can be harmful to a virus, causing it to die out. Others can offer an advantage and help it spread.
"Not every mutation is created equal," said Mary Petrone, who studies infectious diseases at Yale University. "The virus is going to get lucky now and again."
Monitoring variants is important because of the possibility that they could make vaccines and treatments less effective, or change the way they infect people.
A mutation early in the pandemic fueled the spread of the virus around the world, but there had been no notable changes since — until recently, said Ohio State University biologist Daniel Jones.
Drugmakers tweak COVID-19 vaccines to fight variants
First-generation COVID-19 vaccines appear to be working against today’s variants, but makers already are taking steps to tweak their shots if needed. And experts say the mRNA vaccines currently being used in the U.S. by Pfizer and Moderna are easy to update.
Moderna and Pfizer announced that they are prepared to make tweaks to their COVID-19 vaccines and are preparing for a potential booster dose to combat the mutated coronavirus variants circulating around the world.
Kelly Hayes contributed to this story.