COVID subvariant EG.5 and its spawn 'Eris' now dominant in the US

A version of the coronavirus called EG.5 — an offshoot of which is nicknamed "Eris" — now accounts for the largest proportion of new COVID-19 cases in the U.S.

Although EG.5, an omicron subvariant that was first detected in February, is dominating by a slim margin, current data suggest that it is very similar to other versions of omicron spreading throughout the country and no more deadly than its counterparts. 

The Centers for Disease Control and Prevention (CDC) estimates that, between July 23 and Aug. 5, EG.5 made up 17.3% of new cases nationwide, up from 11.9% in the previous two-week period. Those percentages were projected using a model, since the hard genetic data drawn from clinical samples in that time haven't been fully processed, the agency notes on its website.

In the most recent projections, EG.5 narrowly outcompeted another omicron spinoff called XBB.1.16, which was estimated to make up 15.6% of cases. Two more omicron subvariants, XBB.2.23 and XBB.1.5, are trailing close behind at 11.2% and 10.3%, respectively. 

All four of these subvariants belong to the broader XBB lineage, which will serve as the target of the new COVID-19 boosters coming this fall.

Related: Long COVID: 3 years on, here's what we know so far 

Just as EG.5 split from existing branches of the omicron family tree, the subvariant has also sprouted its own offshoots. These include a version of the virus called EG.5.1, which was nicknamed "Eris" on Twitter. T. Ryan Gregory, an evolutionary biologist at the University of Guelph in Ontario, posted this moniker, citing a Wikipedia page about the dwarf planet Eris, named for the Greco-Roman goddess of strife and discord.

In his tweet, Gregory emphasized that the nickname serves only as a convenient way to reference the sublineage, not an indication of its danger. "Note that nickname ≠ expected to cause a big wave by itself," he tweeted.

The World Health Organization (WHO) currently lists EG.5 as a "variant under monitoring," meaning the virus's genetics could theoretically boost its transmissibility or virulence but there isn't enough reliable evidence of that yet. 

EG.5 carries a specific mutation in its spike protein — called S:F456L — which likely helps the virus evade some of the body's immune defenses, according to a report from the Neherlab, a computational biology group based at the University of Basel in Switzerland. EG.5.1, or Eris, carries an additional spike change — S:Q52H — that "might also be a slightly beneficial mutation" for the virus.

Even with these changes, EG.5 is only incrementally different from other subvariants, having evolved slightly to "give it a better ability to engage and enter cells a little bit better," Stuart Turville, an associate professor at the University of New South Wales Sydney, told The Washington Post. 

And the virus doesn't seem to be any more lethal than its counterparts — "the impact on the human body is just about the same," Dr. K. Srinath Reddy, a physician at the Public Health Foundation of India, told the Post.

As of mid-July, XBB.1.16 was still more prevalent than EG.5, on a global scale, the WHO reported. Reports from 100 countries suggest that, at that time, the subvariant accounted for 18.4% of sampled SARS-CoV-2 sequences and EG.5 made up only 11.6% of sequences. But that's compared with 6.2% in the prior month, so the subvariant has been on the rise. 

Notably, the WHO's ability to track the emergence of new subvariants has declined recently, following the organization's decision to end the COVID-19 global health emergency.

"If you look at our latest dashboard that we have, looking at the global circulation of COVID-19, this is in the context of declining surveillance and declining reporting, but this virus is circulating in every country and it is circulating pretty much unchecked," Maria Van Kerkhove, the WHO's COVID-19 technical lead, said during a July 26 press conference. 

Although hospitalization and death rates from the virus have dwindled, "the virus will still circulate and it will still infect individuals, and so it is really critical that countries continue to keep up their surveillance," Van Kerkhove said.