December 4, 2023

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What to know about the EG.5 ‘Eris’ variant and rising Covid hospitalizations

A new coronavirus variant, EG.5, now accounts for the largest proportion of Covid infections in the U.S., according to estimates from the Centers for Disease Control and Prevention.

Over a two-week period ending on Saturday, EG.5 — which some health experts on social media nicknamed “Eris” — made up an estimated 17.3% of new cases nationwide. That’s up from just under 12% during the prior two-week period, and less than 1% as of late May. 

EG.5, like the other strains that have gained dominance in the U.S. over the last year-plus, is a subvariant of omicron. More precisely, it’s considered a descendant of the XBB lineage of the virus. After EG.5, the next most common subvariant, XBB.1.16, accounts for just over 15% of new cases, while XBB.2.23 makes up around 11%. 

Globally, EG.5 accounted for 11.6% of weekly cases in mid-July, up from 6.2% four weeks earlier, according to the World Health Organization. The WHO has categorized it as a variant under monitoring, which is a step below variants of interest or concern. 

The U.K. began monitoring for EG.5.1 — a descendant within the larger EG.5 umbrella — in July, according to the U.K. Health Security Agency. As of July 20, the variant made up 14.5% of cases there. 

The spread of EG.5 comes as the U.S. logs its first increase in hospitalizations of the year. More than 9,000 people were hospitalized with Covid in the last week of July, up from about 6,300 at the end of June. 

However, three experts interviewed for this story said there is not yet evidence that EG.5 is responsible for the rise in hospitalizations. Plus, they said, this summer’s hospitalization rates are still relatively low, and far below the December 2022 peak of over 44,000 weekly Covid hospitalizations.

Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston, said there is no evidence that EG.5 infections cause more severe illness than other omicron subvariants.

EG.5 has likely evolved to become more transmissible than its predecessors, however, as evidenced by its prevalence, Barouch said. But he suggested that widespread immunity from a combination of vaccinations and past infections should keep most people safe from severe illness.

“With EG.5 and likely future variants that will come through the summer, this fall, this winter, we will likely see an increased number of infections and cases,” Barouch said. “But my hope is that we will not see a dramatic increase in severe disease because we have, what I call, a wall of population immunity.”

The updated Covid boosters set to be distributed this fall are not designed to target EG.5. Rather, the Food and Drug Administration asked Moderna and Pfizer in June to target the XBB.1.5 subvariant in their new boosters, since that was the dominant strain at the time. Pfizer said last week that it expects the FDA to sign off on its updated shot by the end of this month. 

Experts said the new boosters may nonetheless offer some protection against EG.5, since the strain is similar to other XBB subvariants.

“They have nearly identical spike proteins, and that’s the basis of the vaccines,” said Andrew Pekosz, a virologist at Johns Hopkins University. “So when the Covid boosters get available this fall, they should be a really nice match for this variant.”

Pekosz said it’s not yet known whether the CDC will issue a general recommendation that all people get the updated boosters, or just people over 60 years old. 

Although some experts continue to debate the usefulness of new Covid boosters for the general population relative to those most vulnerable to severe illness, Pekosz said he thinks it would be smart for most people to get the new shots.

“It’s been a while since we had the bivalent boosters last year, and the variant XBB.1.5 and EG.5 are pretty different from what was in the last booster vaccine,” he said.

There is not yet clinical data about the most common symptoms of EG.5, but they’re unlikely to differ much from those caused by other omicron subvariants, according to Dr. Shan-Lu Liu, co-director of the Viruses and Emerging Pathogens Program at Ohio State University.

These symptoms include fever, cough, fatigue, muscle aches and headache.

“Once we entered the omicron era, the virus has changed from infecting the lungs to more infecting the upper airway,” Liu said. “But symptoms should be pretty common to the previous SARS-CoV-2 infections.”