By LAU­RA UN­GAR-As­so­ci­at­ed Press

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 U.S. 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 U.S. Many peo­ple are tak­ing off their masks and re­turn­ing to in­door spaces like restau­rants and the­aters.

Dr. An­tho­ny Fau­ci, the U.S. gov­ern­ment’s top in­fec­tious dis­ease ex­pert, told ABC’s “This Week” over the week­end that he al­so thinks the U.S. 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.”

The U.K. has “had the same sit­u­a­tion as we’ve had now,” Fau­ci said. “They have BA.2. They have a re­lax­ation of some re­stric­tions such as in­door mask­ing and there’s a wan­ing of im­mu­ni­ty” from vac­cines and past in­fec­tions.

In the U.S., the lat­est da­ta from the Cen­ters for Dis­ease Con­trol and Pre­ven­tion 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% of new in­fec­tions re­port­ed last week.

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% 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 U.S. than the U.K. About 74% of those 12 and old­er are ful­ly vac­ci­nat­ed in the U.S, com­pared with 86% in the U.K.

”We need to em­pha­size that we’re not pro­tect­ed in this coun­try com­pared to peer coun­tries,” Topol said.

Still, not all ex­perts are equal­ly con­cerned about a BA.2-re­lat­ed rise in U.S. cas­es. Dr. James Muss­er, head of ge­nom­ic med­i­cine and in­fec­tious dis­eases at Hous­ton Methodist, said the vari­ant has so far on­ly caused about 1% to 3% of cas­es in his med­ical sys­tem. Cas­es there have usu­al­ly tracked close­ly with what’s hap­pen­ing in the U.K.

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.

Ear­li­er this month, Maria Van Kerk­hove of the World Health Or­ga­ni­za­tion said the hy­brid has been de­tect­ed at “very low lev­els” in France, the Nether­lands and Den­mark. And two re­cent stud­ies, which have not yet been peer-re­viewed, point to a tiny num­ber of cas­es in the U.S.

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 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.

It’s com­mon for coro­n­avirus­es to shuf­fle gene seg­ments, said Dr. Stu­art Camp­bell Ray, an in­fec­tious dis­ease ex­pert at Johns Hop­kins Uni­ver­si­ty. With two vari­ants cir­cu­lat­ing at the same time, peo­ple may get dou­ble in­fec­tions, and a “prog­e­ny virus” could emerge.

Giv­en the virus’ abil­i­ty to spawn new mu­tants — and the rise of BA.2 — ex­perts say peo­ple should get vac­ci­nat­ed if they’re not and keep their masks handy.

“Keep your guard up,” Topol said. “This is not over.”