(NewsNation) — As masks are dropped, there is hope nationwide we are past the worst of the COVID-19 pandemic, but signs from overseas are sparking renewed concerns that yet another new variant is on the horizon.

A descendant of omicron known as BA.2 is now the dominant COVID-19 variant worldwide, causing cases to spike in Europe and Asia and raising preparedness in the U.S.

The World Health Organization says BA.2 now accounts for 75% of global coronavirus cases.

The number of new coronavirus deaths reported worldwide fell last week, but new COVID-19 infections rose, reversing a decline in cases that began in January, according to the WHO.

The biggest increase in cases was seen in the Western Pacific and Africa, where infections rose by 29% and 12%, respectively. 

It’s prompting lockdowns in parts of China, Japan and South Korea.

China banned most people from leaving a coronavirus-hit northeastern province as the fast-spreading variant fuels the country’s biggest outbreak since the start of the pandemic two years ago. 

China’s health authorities also reported two COVID-19 deaths Saturday, the first since January 2021.

Hundreds of cases were reported in other provinces and cities along China’s east coast and inland, as well. Beijing, which had six new cases, and Shanghai, with 41, locked down residential and office buildings where infected people had been found.

The Shanghai Disney Resort has announced that it will close Monday until further notice, citing China’s recent wave of infections.

“Every day when I go to work, I worry that if our office building will suddenly be locked down then I won’t be able to get home, so I have bought a sleeping bag and stored some fast food in the office in advance, just in case,” said Yimeng Li, a Shanghai resident.

Hong Kong, which is facing its worst surge of the pandemic, recorded 16,583 new cases Saturday.

Hong Kong’s cumulative coronavirus infections have exceeded 1 million as the city grapples with a widespread outbreak that has killed more people than the reported COVID-19 deaths in all of mainland China.

The city of 7.4 million is in the grip of a surge that has strained its health care system as hospitals reached maximum capacity. Coffins are running out and mortuaries are so full that bodies have to be temporarily stored in refrigerated containers.

Most of the deceased were elderly patients, a majority of whom are not fully vaccinated.

Experts in the U.S. are watching closely and are seeing cases rise in some parts of the country.

They say Americans should be vigilant, but not to panic.

“We may be in a lull right now, but we also know that there is BA.2 that’s circulating out there,” said Dr. Dana Hawkinson, an infectious disease physician at the University of Kansas Health System. “Still not a large or predominant variant here in the United States — but we know that in other countries it is.”

It already accounts for most of the new cases in the United Kingdom.

In New York, about 30% of new COVID-19 cases are BA.2. And while cases and hospitalizations are still way down from their last peak in January, experts say the variant needs to be on our radar.

Front-line health care workers, who’ve been at war with COVID-19 and its variants, delta and omicron, say they’re well prepared for whatever comes next.

“And I think as we go forward — as we move forward — it’s more a question of how are we gonna handle this,” said New York ER nurse Zuleima Vega.

Right now, the biggest concern is the new variant’s transmission rate. While the sub-variant BA.2 is about 50% to 60% more transmissible than omicron, it does not appear to be more severe.

“It has a degree of transmission advantage over the original omicron. Which means, ultimately over time, it might take over as the dominant variant,” Dr. Anthony Fauci, White House Chief Medical Adviser, said on ABCNews. “The bottom line is we will likely see an uptick in cases, as we’ve seen in the European countries — particularly the UK.”

Fauci says an uptick in cases doesn’t need to mean another COVID-19 surge as long as people continue to get vaccinated and the vaccinated consider getting boosted.

The Associated Press contributed to this report.