Just in time for respiratory virus season, a highly transmissible COVID-19 strain is fueling a wave of infections across the US.
The XFG variant, informally known as “Stratus,” has been driving up case numbers. Stratus’ ability to evade immune system defenses has propelled it past NB.1.8.1 (aka “Nimbus”) as the dominant Covid strain.
The increased Covid activity comes as the US heads into fall respiratory illness season — which tends to bring a rise in cases of the common cold, flu and respiratory syncytial virus (RSV) — and amid evolving guidance for Covid vaccines.
The level of Covid viral activity in wastewater is “moderate” nationally, according to Sept. 20 data, the latest available from the Centers for Disease Control and Prevention.
Nineteen states are reporting “high” or “very high” levels of the virus in wastewater, with Nevada, Utah, Connecticut and Delaware leading the way.
Stratus, a hybrid of two Omicron sub-strains, was initially detected in January in Southeast Asia and in the US in the spring.
It had spread to 38 countries by June, prompting the World Health Organization to describe it as a “variant under monitoring.”
Stratus is known to cause hoarseness and a scratchy or sore throat, which can be mistaken for allergies.
Stony Brook Medicine reports that most Stratus cases are mild, especially for those who are vaccinated.
Yet the strain carries unique mutations that enhance its ability to evade antibodies gained from prior Covid infections or vaccinations.
That it’s been able to surpass Nimbus is surprising since Nimbus is skilled at binding to human cells, allowing it to spread quickly.
An Omicron subvariant, Nimbus wreaked havoc this summer in the US.
It’s known for causing a severe sore throat, ominously called “razor blade” throat.
To protect against Covid and other respiratory viruses, health experts advise practicing good hygiene, improving indoor air ventilation and filtration and staying up to date with vaccines.
The CDC’s Advisory Committee on Immunization Practices (ACIP) recently recommended the 2025-2026 updated Covid vaccines for anyone 6 months and older after consulting a doctor or pharmacist.
