Experts warn Omicron variant may push Covid cases up in US

With coronavirus cases rising in parts of Europe and Asia, scientists worry that an extra-contagious version of the Omicron variant may soon push cases up in the United States too.

Experts are also keeping their eyes on another mutant: a rare Delta-Omicron hybrid that they say doesn't pose much of a threat right now but shows how wily the coronavirus can be.

The US will likely see an uptick in cases caused by the Omicron descendant BA.2 starting in the next few weeks, according to Dr Eric Topol, head of Scripps Research Translational Institute.

"It's inevitable we will see a BA.2 wave here," he said.

One reason? After about two months of falling Covid-19 cases, pandemic restrictions have been lifted across the US. Many people are taking off their masks and returning to indoor spaces like restaurants and theaters.

Dr. Anthony Fauci, the US government’s top infectious disease expert, told ABC's "This Week" over the weekend that he also thinks the US will likely face an "uptick" similar to what's happening in Europe, particularly the United Kingdom, where BA.2 is the dominant strain. 

He said he doesn't think it will be a "surge."

READ MORE: US pregnancy deaths show massive toll on Black women in first Covid year

New variant 'coming onto the scene'

In the US, the latest data from the Centers for Disease Control and Prevention (CDC) shows overall Covid-19 cases have been trending down. But the share caused by BA.2 is up significantly; the variant accounted for about 35 percent of new infections reported last week. In the Northeast, it was about half.

Keri Althoff, a researcher at Johns Hopkins Bloomberg School of Public Health, cautioned that CDC case counts underestimate the true numbers because some people are no longer getting tested and others are testing at home and not reporting the results. Also, she said, not every specimen is genetically sequenced to determine the variant.

It’s clear, she said, "BA.2 is coming onto the scene."

One reason the variant has gained ground, scientists say, is that it's about 30 percent more contagious than the original Omicron. In rare cases, research shows it can sicken people even if they've already had an Omicron infection — although it doesn't seem to cause more severe disease.

Vaccines appear just as effective against both types of Omicron, but breakthrough infections are possible. And experts point out that vaccination rates are lower in the US than in the UK. About 74 percent of those 12 and older are fully vaccinated in the US, compared with 86 percent in the UK. 

"We need to emphasise that we're not protected in this country compared to peer countries," Topol said.

READ MORE: US considers approving second Covid booster shot

'Deltacron'

Still, not all experts are equally concerned about a BA.2-related rise in US cases. Dr James Musser, head of genomic medicine and infectious diseases at Houston Methodist, said the variant has so far only caused about 1 percent to 3 percent of cases in his medical system. 

Cases there have usually tracked closely with what's happening in the UK.

He called BA.2 "something we’re keeping an eye on," but said, "I’m not losing sleep" over it.

That’s how many scientists view the other variant that some in the public are calling "Deltacron," a hybrid containing genetic information from both Delta and Omicron. 

Much remains unknown about the hybrid. 

There's no evidence it causes more severe disease, and it doesn't look like it's infecting many people. CDC researchers identified 9 samples, seven from the mid-Atlantic region in a study released on Monday that hasn't yet been peer-reviewed. Topol, who was not involved in the research, said there's no evidence it has the potential to spread.