As the fall season begins, COVID-19 cases are still climbing in much of the United States. The country has yet to emerge from a late summer COVID wave driven by the new “Stratus” variant, which is sickening Americans from coast to coast.
As TODAY.com reports, as of Sept. 13, the level of COVID-19 viral activity in wastewater is “high” nationally, according to the latest data from the U.S. Centers for Disease Control and Prevention (CDC). At least 29 states are reporting “high” or “very high” levels of COVID in wastewater, per the CDC. Hotspots include California, Utah, Indiana, Florida, Alabama and North Carolina.
The rise in cases comes as confusion grows around who is eligible to get the updated COVID-19 vaccines this fall.
Although the uptick is concerning, especially amid shifting vaccination guidelines, it isn’t a surprise to many experts. COVID-19 cases have spiked every summer since the pandemic began. The SARS-CoV-2 virus mutates often, giving rise to new strains of the virus that are often more transmissible and better at escaping immunity than their predecessors.
The current COVID surge is being driven by the mutated XFG variant, aka “Stratus,” which is spreading rapidly worldwide. XFG was first detected in the U.S. in March, but it took several months for the strain to surpass the NB.1.8.1 or “Nimbus” variant. Currently, Stratus is the dominant variant circulating in the U.S., according to wastewater data from the CDC.
It’s unclear when this summer wave will end. As of Sept. 16, the CDC estimates that COVID infections are still growing or likely growing in 9 states, not changing in 12 states, and declining or likely declining in 24 states, according to forecasting models.
What is the Stratus variant, which symptoms does it cause, and will COVID vaccines protect against it?
What Is the XFG “Stratus” Variant?
XFG was first detected in January in Southeast Asia. In June, the World Health Organization classified XFG as a “variant under monitoring” due to its rapid global spread. “(XFG) is part of the very large omicron family of variants,” Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, tells TODAY.com. XFG is a recombinant or hybrid of two existing omicron strains, LF.7 and LP.8.1.2, according to the WHO.
This means XFG has a mixture of genetic material from these two variants, which may make it better able to bind to cells in the body and cause infection, Dr. Albert Ko, professor of public health, epidemiology and medicine at Yale School of Public Health, previously told TODAY.com. “NB.1.18.1 (Nimbus) and XFG (Stratus) appear to be more transmissible compared to other variants,” Ko said.
XFG also has several unique mutations in its spike protein, which have been shown to improve the virus’s ability to evade COVID-19 antibodies from prior infection or vaccination, per the WHO. However, the WHO assesses the public health risk posed by XFG to be “low,” and current data do not indicate that Stratus causes more severe illness. “All these newer omicron variants are highly contagious, but apparently not as severe,” says Schaffner.
XFG was given its cloud-themed nickname “Stratus” on “X” by evolutionary biologist T. Ryan Gregory, who also coined “Nimbus” and other popular variant names.
XFG “Stratus” Variant Now Dominant in US
In early May, XFG accounted for less than 3% of infections in the U.S., per the CDC’s Nowcast estimates. However, Stratus surged in June and July. During the four-week period ending Aug. 30, XFG accounted for an estimated 78% of COVID cases.
Wastewater sequencing data also show Stratus is the dominant variant in the U.S. As of Sept. 6, XFG accounts for over 80% of wastewater samples sequenced by the CDC.
The CDC has not published data on the regional spread of XFG, but according to the Global Initiative on Sharing All Influenza Data (GISAID) open-access database, XFG has been spreading in most U.S. states since July.
Is Stratus Causing a Late Summer Wave?
COVID can spike throughout the year, but tends to cause two distinct waves in the U.S., one in the winter and another in the summer. These surges are driven by new variants and decreasing immunity from prior infection and vaccination, as well as summer travel, experts note.
The 2025 summer COVID wave began around July. It’s hard to tell when it will wane, and a lack of data has made it harder to track COVID in real-time, TODAY.com reported previously.
Data from the CDC and WastewaterSCAN, which monitors diseases through municipal wastewater systems, show that COVID viral activity levels are still “high” across the country. “There has been a significant upward trend in the past 21 days,” a spokesperson for WastewaterSCAN told TODAY.com on Sept. 17. “We are seeing detections peak later this year than in past years, with no indication that we’ve reached a peak yet,” the spokesperson added.
As of Sept. 6, the weekly COVID test positivity rate was 10.8%, a slight decline from the previous week, per the CDC. During the peak of last summer’s COVID wave, it was 18%.
The Pandemic Mitigation Collective’s COVID forecasting model, which uses data from various sources, estimates there are 1.3 million new daily infections in the U.S. as of Sept. 15. Emergency department visits for COVID-19 and hospitalizations are just starting to stabilize after rising for most of August into early September, per CDC data.
The current rate of hospitalizations is still much lower relative to the rate seen earlier in the pandemic, Schaffner notes. “I can’t tell you how bad this or how severe this current summer increase will be, but certainly the metrics show that we’re still having that late summer wave,” says Schaffner.
Symptoms of XFG Stratus Variant
Currently, the symptoms of Stratus appear to be very similar to other recent omicron variants. There’s no evidence that XFG causes distinct symptoms, says Schaffner.
Common symptoms of the Stratus variant include:
- Sore throat
- Cough
- Congestion or runny nose
- Fever or chills
- Shortness of breath
- New loss of sense of taste or smell
- Fatigue
- Headache
- Muscle aches
- Nausea, vomiting or diarrhea
Recently, there have been anecdotal reports that the Stratus and Nimbus variants cause “razor blade throat” or hoarseness. However, a painful, sore throat has been a well-documented COVID symptom since 2020, says Schaffner.
The severity and duration of COVID-19 symptoms can vary from person to person. It’s impossible to tell whether you have COVID-19 from symptoms alone, which is why testing is important. If you test positive, you can seek treatment with antivirals, such as Paxlovid, which are most effective when taken early, says Schaffner.
People at high risk of severe illness can benefit the most from treatment, he adds. These include adults over the age of 65, people who are immunocompromised and people with underlying health conditions.
Who Should Get the COVID Vaccine?
COVID-19 vaccination is safe and highly effective at preventing severe illness, complications and death from COVID-19. Currently approved COVID vaccines are expected to remain effective against the XFG variant, the WHO said. “Given these dominant strains now are part of the omicron family, last year’s vaccine and the anticipated updated vaccines should cover these new strains,” says Schaffner.
Schaffner recommends high-risk individuals consider getting a COVID-19 vaccine to carry them through the fall and winter. Always talk to your doctor if you have questions. The updated 2025-2026 COVID shots, which target LP.8.1, have been approved by the U.S. Food and Drug Administration (FDA), but with restrictions that limit who is eligible to get the shot. The FDA only authorized the shots for people over the age of 65 and those with a condition that puts them at high risk for severe COVID.
Everyone else may face hurdles to get vaccinated, such as needing a prescription from a doctor. The recent changes to CDC vaccination guidelines could also make it harder for certain groups to get the shot, including children and pregnant women.
However, the American Academy of Pediatrics (AAP) “strongly recommends” COVID-19 vaccines for children ages 6 months to 2 years. The American College of Obstetricians and Gynecologists (ACOG) also recommends updated COVID-19 vaccines for pregnant and lactating women.
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