Called XEC, this emerging sublineage stems from the Omicron variant of SARS-CoV-2, the coronavirus that causes COVID-19. The strain had been detected in at least 15 countries and 12 U.S. states as of Sept. 3, according to Outbreak.info, a Scripps Research COVID database. 

“At this juncture, the XEC variant appears to be the most likely one to get legs next,” Dr. Eric Topol, founder and director of the Scripps Research Translational Institute, posted on X last week. His remarks were in response to a post by Mike Honey, a data analyst in Australia who had charted XEC’s origins from Berlin, first appearing in June.

XEC’s growth in recent weeks has been strongest in Denmark and Germany, followed by the U.K. and the Netherlands, Honey’s analysis shows. Outbreak.info reported 95 XEC infections worldwide as of Sept. 3, from Canada to Italy to Taiwan, but hasn’t been updated since. Honey posted Sept. 14 that his data indicated the subvariant had spread to more than 500 cases in 27 countries, including China and Ukraine.

At this juncture, the XEC variant appears to be the most likely one to get legs next. Its current status nicely tracked by @Mike_Honey_ 's threadhttps://t.co/4AnLa3MXfz

— Eric Topol (@EricTopol) September 15, 2024

While XEC is on the move, its prevalence remains relatively low in the U.S., according to the Centers for Disease Control and Prevention (CDC). An Omicron sublineage called KP.3.1.1 (and nicknamed “DeFLuQE”) has recently taken over, accounting for 53% of infections nationwide from Sept. 1–14, per the CDC’s COVID Data Tracker. XEC isn’t pervasive enough to even appear on the tracker—it would have to account for at least 1% of infections in a two-week span—but that may not be the case for long.

XEC “could surpass KP.3.1.1 in the coming weeks,” Andrea Garcia, MPH, American Medical Association (AMA) vice president of science, medicine, and public health, said in the Sept. 6 episode of the AMA Update podcast. “There’s not a lot of data on this new subvariant at this point in time.”

XEC, according to Topol, is a combination of Omicron sublineages KS.1.1 and KP.3.3.

What are the symptoms of XEC infection?

The CDC has yet to pinpoint symptoms specific to XEC infection, but take note of these typical COVID-19 symptoms: 

• Congestion or runny nose
• Cough
• Diarrhea
• Fatigue
• Fever or chills
• Headache
• Muscle or body aches
• New loss of taste or smell
• Nausea or vomiting
• Shortness of breath or difficulty breathing
• Sore throat

These symptoms, the CDC says, warrant emergency medical care:

• Inability to wake or stay awake
• Lips, skin, and nail beds that appear pale, blue, or gray
• New confusion
• Persistent pain or pressure in the chest
• Trouble breathing

Does the new COVID vaccine protect against XEC?

The new 2024–25 COVID vaccines—manufactured by Pfizer, Moderna, and Novavax—arrived earlier than expected and are widely available at pharmacies, health departments, urgent care centers, and other health care providers.

The Pfizer and Moderna vaccines are mRNA-based and earmarked for the Omicron KP.2 strain. The protein-based Novavax vaccine targets its parental lineage, JN.1. While they weren’t engineered to combat XEC per se, they were manufactured with the family of recently circulating variants in mind.

The CDC recommends everyone aged 6 months and older get an updated vaccine to protect themselves and their loved ones against severe infection, hospitalization, and death. 

“Vaccination continues to be the cornerstone of COVID-19 prevention,” Dr. Peter Marks, director of the Food and Drug Administration’s Center for Biologics Evaluation and Research, said in a news release last month. “Given waning immunity of the population from previous exposure to the virus and from prior vaccination, we strongly encourage those who are eligible to consider receiving an updated COVID-19 vaccine to provide better protection against currently circulating variants.”

Most U.S. adults are eligible for a free vaccine through their private health insurance, Medicare, and Medicaid plans, the CDC says. The agency’s Vaccines for Children Program provides immunizations for children 18 and younger. Visit Vaccines.gov to find a location near you. You can also call 800-232-0233 or text your ZIP code to 438829.

Where is COVID spreading in the U.S.?

The nation is coming down from what CDC records show was its biggest COVID summer surge yet. Test positivity was 3.1% the week ended May 11, climbing consistently before peaking at 17.8% the week ended Aug. 10. Though that rate has ticked down, it’s still higher than it was at this time last year, with test positivity projected to be 14.9% the week ended Sept. 7.

We’re not out of the woods yet. In the four weeks from Aug. 11–Sept. 7, the national test positivity rate was 17.1%, and no U.S. region had a rate below 10%. The five states that make up the CDC’s Region 6—Arkansas, Louisiana, New Mexico, Oklahoma, and Texas—had the highest test positivity, 20.5%.

In addition, the national wastewater viral activity level remained “high,” the second-most severe rating, the week ended Sept. 7. 

For more on COVID-19: 

• New COVID vaccines are here. What to know about latest shots in wake of nation’s biggest summer surge
• Free, at-home COVID tests are back. Here’s how to order yours
• Could it be COVID? Here are the symptoms to watch out for in 2024
• Got COVID? Here are the new 2024 isolation guidelines
• COVID sickens older adults most severely, but less than half say they’ll get the new vaccine