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The World Health Organization announced Thursday it had stepped up its classification of a recently discovered COVID-19 strain, BA.2.86, citing its large number of mutations.

This strain’s rapid escalation to the WHO’s “variant under monitoring” category is uncommon. Just four cases have been spotted of the variant worldwide. Virus trackers officially designated the strain as BA.2.86 less than a day ago.

It is too early to say whether the variant will be more dangerous than the currently circulating strains of the virus. But the U.N. agency says more data is needed to understand the threat BA.2.86 might pose, given its large number of mutations.

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.

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

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 sample was sequenced 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.

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. The two cases spotted there had “no epidemiological link” and were not immunocompromised. 

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. 

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.