The U.S. Centers for Disease Control and Prevention announced Thursday it is tracking a recently discovered COVID-19 strain, BA.2.86, after a case of the highly mutated variant was discovered in Michigan.

"Today we are more prepared than ever to detect and respond to changes in the COVID-19 virus. Scientists are working now to understand more about the newly identified lineage in these 4 cases and we will share more information as it becomes available," CDC spokesperson Kathleen Conley said in a statement to CBS News.

Experts say reports of BA.2.86 being spotted in countries on multiple continents — Denmark, Israel, U.K. and U.S. — suggest it is at least capable of transmitting widely and could have been spreading undetected for some time.

It comes after the World Health Organization announced it had classified BA.2.86 as a "variant under monitoring" due to its large number of mutations.

This strain's rapid escalation to the WHO's "variant under monitoring" category is uncommon. Just three cases had been spotted of the variant worldwide. Virus trackers officially designated the strain as BA.2.86 just a day ago.

It is too early to say whether the variant will be more dangerous than the currently circulating strains of the virus. The U.N. agency says more data is needed to understand the threat BA.2.86 might pose, but had accelerated the classification due to its sheer number of changes.

The strain's dozens of genetic changes — an evolutionary jump on par with the emergence of the original Omicron variant in 2021 — has raised eyebrows among virologists as cases have started to crop up around the world. Its mutations include some changes at key parts of the virus that could help it better dodge the body's immunity from prior infections or vaccination.

"Deep mutational scanning indicates BA.2.86 variant will have equal or greater escape than XBB.1.5 from antibodies elicited by pre-Omicron and first-generation Omicron variants," Jesse Bloom, an evolutionary biologist at the Fred Hutch Cancer Center, said in a slide deck published Thursday.

XBB.1.5 is the variant from which many recent strains have descended, and Food and Drug Administration officials had previously picked out XBB.1.5 as the strain for vaccines to target in this fall's booster shots.

BA.2.86 has 36 mutations relative to the XBB.1.5 variant, Bloom said.

The first U.S. case of BA.2.86 was reported by a lab at the University of Michigan. According to records attached to the sequence uploaded to GISAID, a global virus database, the variant was sequenced from a sample collected by the university's clinical microbiology lab during "baseline surveillance."

It is unclear whether the samples were collected from a hospitalized patient in the health system run by the university or from another source. A spokesperson for the University of Michigan Medical School declined to comment on the possible origin of the sequence, deferring to Michigan's state health department. A spokesperson for Michigan's Department of Health and Human Services was not able to immediately answer a request for comment.

Dr. Adam Lauring, a University of Michigan professor who runs the lab that sequenced the case, said Friday that they sequence cases from a large area in Michigan for the state health department and CDC. He declined to share additional details about the variant infection, which he said is now being investigated by health authorities.

Lauring's lab sequences cases from both hospitalized and non-hospitalized patients, he told CBS News in an email.

In Denmark, health authorities say they are currently working to culture the virus, a key step towards further assessing the threat posed by the highly mutated strain. Three cases have been spotted there, the Statens Serum Institute said. None had prior contact with each other and all experienced common COVID-19 symptoms.

Researchers in the U.K. have also identified at least one case, Luke Blagdon Snell, a researcher at Kings College London, said Friday. The patient was hospitalized and likely acquired their infection locally.

Tracking the spread of COVID variants BA.2.86 and EG.5

For now, experts say BA.2.86 will still need to show it can outcompete other fast-spreading descendants of the XBB Omicron variant already on the rise around the world in order to be more than a "scientific curiosity."

One XBB descendant, a variant called EG.5, had already climbed to nearly 1 in 5 cases nationwide as of CDC estimates published earlier this month.

New projections are due to be published Friday by the CDC. The agency says BA.2.86 will remain aggregated with its distant parent, the Omicron variant known as BA.2, until it reaches 1% prevalence in its weighted estimates.

The strain's emergence comes as drugmakers have been preparing to roll out new COVID-19 vaccines next month aimed at the XBB strains of the virus, of which EG.5 is closely related. Moderna announced Thursday that its preliminary clinical trial data from the new shots confirmed "a significant boost in neutralizing antibodies" for EG.5.

Those could face a setback if BA.2.86 is able to spread more widely. Bloom said he thinks the strain's changes are enough to risk making the XBB-targeted vaccines a "fairly poor match" to BA.2.86.

But he underscored that BA.2.86 remains rare for now, and other defenses mounted by the body may also still work to fend off the highly mutated variant.

"[T]here are also broader mechanisms of immunity elicited by vaccination and infection that provide some protection against severe disease even for very heavily mutated variants," he told CBS News in an email.

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