Covid-19 cases have been dropping significantly in the United States and throughout the rest of the world, prompting many leaders to lift pandemic restrictions. But health experts caution that the "stealth" subvariant of omicron, called BA.2, may be cause for concern despite falling case numbers. The subvariant could slow the recent decline in cases and serves as a reminder that other coronavirus variants could arise.

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Covid-19 cases drop and vaccination rates slow

The World Health Organization (WHO) on Tuesday announced that Covid-19 cases worldwide last week dropped 21% and Covid-19 deaths dropped 8%, marking the first time deaths have dropped since early January.

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Covid-19 cases are decreasing even more precipitously in the United States. According to data from Johns Hopkins University, around 84,000 new Covid-19 cases are being reported each day in the United States, representing a 90% drop over the past five weeks. And a CNBC analysis of the Johns Hopkins data found that every U.S. region is reporting at least a 40% drop in cases over the past two weeks.

Hospitalizations have also dropped, with around 66,000 people hospitalized with Covid-19 in the United States, down from a peak of 159,000 on Jan. 20. Covid-19 deaths are still elevated, however, but death rates typically lag behind rises in case numbers, CNBC reports. Still, death rates have fallen below 2,000 per day, down from almost 2,600 per day on Feb. 1.

"While we're not where we all want to be yet, we're encouraged by the dramatic declines we're seeing in cases and hospitalizations nationwide," Jeff Zients, the White House Covid-19 response coordinator, said.

Given the drop in cases and hospitalizations, many U.S. leaders are lifting Covid-19 restrictions, such as mask requirements and, in some instances, vaccine mandates for indoor spaces.

However, vaccination rates across the United States have stagnated. Around 90,000 Americans are getting their first shot of a Covid-19 vaccine each day in the United States, the lowest number since the start of the U.S. vaccination campaign, the Associated Press reports. So far, around 76% of the U.S. population has received at least one shot of a vaccine, and less than 65% of Americans are fully vaccinated.

"People heard more stories about, well, the omicron's not that bad," Kathy Emmons, executive director of the Cheyenne-Laramie County Health Department in Wyoming, said. "I think a lot of people just kind of rolled the dice and decided, 'Well, if it's not that bad, I'm just going to kind of wait it out and see what happens.'"

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Should BA.2 cause concern?

While Covid-19 cases are dropping, health experts warn that BA.2 may slow that decline. According to WHO, BA.2 is around 30% more transmissible than the original strain of omicron. So far, the subvariant accounts for more than a third of all recently sequenced Covid-19 cases globally.

According to the Wall Street Journal, the recent rise of the subvariant is prompting some health experts to question whether leaders are relaxing Covid-19 precautions too soon. However, governments are pointing to current rates of Covid-19 immunity, both through vaccination and infection, along with a "weary" public, as reasons to continue fully reopening, the Journal reports.

Jennifer Nuzzo, an epidemiologist at Hopkins, said, "I don't think BA.2 is going to cause the huge spike that we saw in the winter," also pointing to the current levels of immunity after the omicron wave. "But it's possible it could drag out the decline, the rate of slowdown."

While BA.2 has been found to be more transmissible than the original strain of omicron, research has found it's not more likely to cause severe disease, with the authors of one study saying that, "while BA.2 may have a competitive advantage over BA.1 in some settings, the clinical profile of illness remains similar."

"While it may become a dominant strain in time, it appears increasingly unlikely that it will cause a significant change in the downward trajectory of the current epidemic wave," former FDA Commissioner Scott Gottlieb said.

"The bottom line is we're relatively optimistic that things will continue to improve through the spring and the summer under omicron," Matt Craven, a partner at McKinsey who specializes in public health and infectious disease, said.

However, BA.2 "serves as that reminder we very well may not be done here and there may be others coming," he added. (Beals, The Hill, 2/23; Kimball/Rattner, CNBC, 2/22; Reeves/Stobbe, Associated Press, 2/23; Reed, Axios, 2/24; Fiore, MedPage Today, 2/23; Landers/Inada, Wall Street Journal, 2/23)