In this March 4, 2022, file photo, patrons celebrate "Happy Friday" maskless indoors at the Grand Central Los Angeles in Los Angeles. Credit: Damian Dovarganes / AP

COVID-19 cases are dropping in California and across the country to levels not seen since before last summer’s nasty delta variant took hold. Face mask requirements have been lifted. The Centers for Disease Control and Prevention’s risk maps have shifted from red and orange warning colors to reassuring yellow and green.

So why are many health experts feeling uneasy?

There are troubling signs on the horizon that this may be a short reprieve from the virus now in its third year of upending our lives. Cases are rising sharply across Europe and Asia, driven by a more transmissible sublineage of the super-contagious omicron variant that sent cases soaring over the winter. And that new sub-variant — which has been dubbed “stealth omicron” — is steadily gaining ground in the U.S.

“We should definitely be concerned,” said Dr. Eric Topol, executive vice president at Scripps Research in La Jolla and professor of molecular medicine. “We’re going to see a significant surge here.”

The World Health Organization’s director general Thursday said that “after several weeks of declines, reported cases of COVID-19 are once again increasing globally, especially in parts of Asia,” and added that because of reductions in testing, “the cases we are seeing are just the tip of the iceberg.”

“The pandemic is not over,” WHO Director-General Tedros Adhanom Gebreyesus said.

The WHO’s Dr. Maria Van Kerkhove attributed the global upturn in cases to the timing of the BA.2 variant’s spread just as many countries, particularly in Europe, relaxed public health measures like requiring face masks and limiting crowds.

She warned that confusing messaging from government and public health officials led to “misinformation that omicron is mild, misinformation that the pandemic is over, misinformation that this is the last variant that we will have to deal with.”

What’s that mean for us here in California and the rest of the country? Topol and other experts are troubled that California and other states have loosened pandemic restrictions in recent weeks, and the U.S. has lower rates of vaccination and booster doses than other countries experiencing spikes in infections. In the past, outbreaks in the U.S. have followed foreign case surges by only a few weeks.

Consider the comparison to countries seeing significant cases: The United Kingdom and Germany in Europe and South Korea and Vietnam in Asia. The percentage of the population fully vaccinated is 74 percent in the U.K. and 76 percent in Germany, and both countries report 58 percent are boosted, according to New York Times data. South Korea is 86 percent fully vaccinated and 62 percent boosted, Vietnam 80 percent fully vaccinated and 44 percent boosted.

The same data show the U.S. is 65 percent fully vaccinated and 29 percent boosted.

“This is coming here to a place near you,” Topol said. “It’s just a matter of time.”

By at least one measure seen as an early indicator of virus activity, it’s already happening. Of the 485 wastewater systems the CDC is monitoring across the country to check for the COVID-19 virus, 193 reported increases in the past week. In California, they included systems serving San Benito County, Los Angeles and Ventura.

Santa Clara County Health Officer Dr. Sara Cody said BA.2 is already showing up in wastewater from the northern end of the county, although virus infection levels have remained low throughout the county and cases haven’t reversed their downward trend.

“It is not driving up the levels overall,” Cody said. “I don’t know why, but it isn’t. But we’re watching that very, very carefully here and elsewhere.”

Dr. John Swartzberg, professor emeritus of infectious diseases and vaccinology at the University of California at Berkeley, said the BA.2 subvariant is 30 percent more transmissible than the BA.1 omicron subvariant that drove the record winter case surge. Reports from the United Kingdom show the subvariant’s growth has coincided with the country’s upturn in cases, with BA.2 jumping from 52 percent of cases Feb. 20 to 83 percent March 6.

The subvariant hasn’t reached those levels in the U.S. — yet. But Swartzberg noted it has grown rapidly, from 4 percent Feb. 19 to 7 percent Feb. 26 to 14 percent March 5 and 23 percent March 12.

“It’s doubling here about every week, which means if this continues, it should become the dominant variant we’ll be dealing with here in the United States within two weeks,” he said. “We’ll be dealing with a variant that’s about 30 percent more transmissible in a couple of weeks if not sooner.”

The highly contagious virus has infected several high-profile political leaders in the past week, including former President Barack Obama, Vice President Kamala Harris’ husband Doug Emhoff, and San Jose Rep. Zoe Lofgren.

Even so, Washington officials, while acknowledging the threat, aren’t sounding the alarm, maintaining that with funding for tests, treatments and vaccines — the White House has asked for $22.5 billion — the country is well-positioned to manage COVID-19 outbreaks.

White House press secretary Jen Psaki said Thursday that BA.2 “has been circulating here for some time” and that “we are closely watching and monitoring the situation both in Europe and in China.”

“But we do know the tools the United States has — including the mRNA vaccines, therapeutics and tests — all are effective tools against this variant,” Psaki said.

Those comments have left health experts like Swartzberg feeling like Cassandra of Greek mythology as they watch COVID-19 surges overseas and warn that relaxed public health measures here are still needed.

“You can see the future, but nobody listens to you,” Swartzberg said. “Bottom line, we’re just not through with this virus.”

Story by John Woolfolk, Mercury News.