By Marin Wolf, The Dallas Morning News (TNS)

Public health experts are monitoring a sub-lineage of the COVID-19 omicron variant that is spreading in several European and Asian countries.

Scientists discovered the sub-lineage, called BA.2, in December, shortly after the original omicron lineage, called BA.1, was identified. Recent spread of the sub-lineage led the U.K. Health Security Agency to designate BA.2 as “under investigation.”

In Denmark, BA.2 jumped from 20% of COVID-19 cases in the last week of December to 45% of cases in the second week of January, according to Danish public health organization Statens Serum Institut.

Fewer than 100 cases of BA.2 have been reported in the U.S., a mere fraction of the more than 660,000 omicron cases detected in the country in the last week, according to the Centers for Disease Control and Prevention. .

While BA.2 has the potential to take over omicron as the dominant variant in the U.S., it’s too early to tell what impact it will have on the pandemic, said Dr. Wesley Long, medical director of diagnostic microbiology at Houston Methodist.

“In the U.S., we have to wait and see what the story is on BA.2 and how it compares to BA.1,” he said. “It’s worth keeping an eye on right now.”

Here’s what experts know so far about the sub-lineage – and what they know about other future COVID-19 variants.

How does BA.2 differ from omicron’s original lineage?

BA.1 and BA.2 have a handful of differences in their genomes, including in the spike protein, which impacts how easily the strains can be differentiated, said Dr. Jeffrey SoRelle, who is leading the University of Texas Southwestern’s COVID-19 variant tracking effort.

One of the early systems for differentiating omicron from previous variants is a PCR test that looks for three different genomic targets, he said. BA.1 has a mutation at the site of one of the targets, causing that specific target to fail. BA.2 does not have that mutation, so it can’t be differentiated from delta in the same way.

BA.2′s ability to avoid differentiation through that early testing system secured the sub-lineage the nickname of the “stealth” omicron variant. The nickname, however, is a bit of a misnomer, SoRelle said.

“Our sequencing can still detect it, our diagnostic testing can still detect it, antigen tests should still be able to detect it,” he said.

Should we be worried about BA.2?

Early data out of Denmark shows that BA.2 appears to be more transmissible than BA.1, SoRelle said. It’s possible that BA.2 will take over as the dominant strain everywhere, just as BA.1 did to the delta variant, although scientists won’t know for some time.

There’s no current evidence to suggest that BA.2 causes more severe illness than BA.1, Long said. Experts are watching to see whether BA.2 is any better at evading the COVID-19 vaccine than its fellow omicron sub-lineage.

Because BA.1 and BA.2 are somewhat closely related, it’s possible that people recently infected with omicron will be less likely to become infected with BA.2 in the near future, said Jeremy Kamil, associate professor of microbiology and immunology at Louisiana State University Health Shreveport.

“We know that a lot of people’s natural defense against delta wasn’t sufficient to stop them from being infected by omicron,” he said. But, “I’m quite skeptical that someone who’s recovered from BA.1 is going to be a good host for BA.2. I sincerely doubt it.”

While BA.2 is worth monitoring, experts say it’s not a major point of concern right now. “I don’t think it’s worth being worried about BA.2, in particular, more than one would already be concerned about omicron BA.1. I think it’s something we need to keep an eye on,” Long said.

What other variants can we expect to develop after omicron?

Experts say it’s very possible that another coronavirus variant will develop after omicron cases die down, especially because of how transmissible omicron is. The more a virus is transmitted, the more opportunities it has to mutate and give rise to a new strain.

“As long as COVID is transmitted, especially in areas where there are low vaccination rates, we are at risk of having a new variant emerge that, through immune evasion or an increase in transmissibility, could start another wave [of COVID-19],” Long said.

What that potential new variant will look like is less clear.

“Every single variant has been very different in characteristics, so it’s hard to extrapolate too much into the future, SoRelle said. “Even though [omicron] was less severe, it was much more transmissible and it put more people in the hospital at one time than did the delta strain, for instance.”

Even if their emergence is possible, new variants are not necessarily inevitable. So far, variants have developed in countries with low vaccination rates, so focusing on increasing overall vaccination rates could lower the risk of new variants developing, SoRelle said.