As the United States braces for the fall respiratory illness season, a highly contagious strain of COVID-19, informally known as “Stratus,” is causing a surge in infections. This variant, officially designated as XFG, has surpassed the previously dominant strain, NB.1.8.1 or “Nimbus,” due to its enhanced ability to evade the immune system. This uptick in COVID-19 cases coincides with the typical increase in common cold, flu, and respiratory syncytial virus cases that occur during the fall season.
The Stratus variant has been instrumental in driving up the number of COVID-19 cases, just as the country prepares for the respiratory virus season. According to data from the Centers for Disease Control and Prevention (CDC) dated September 20, the national level of COVID viral activity in wastewater is currently classified as “moderate.” However, 19 states are experiencing “high” or “very high” levels of the virus in wastewater, with Nevada, Utah, Connecticut, and Delaware being the most affected.
Stratus, a hybrid of two Omicron sub-strains, was first identified in Southeast Asia in January and later in the US during the spring. By June, it had spread to 38 countries, leading the World Health Organization to classify it as a “variant under monitoring.” Symptoms of the Stratus variant include hoarseness and a scratchy or sore throat, which can often be mistaken for allergies.
Health experts strongly advise those who are ill with a virus to stay home to prevent further spread. Most cases of the Stratus variant are mild, particularly in vaccinated individuals, according to Stony Brook Medicine. However, the strain possesses unique mutations that enhance its ability to evade antibodies from previous COVID infections or vaccinations.
The fact that Stratus has overtaken Nimbus is surprising, given Nimbus’s proficiency at binding to human cells, which enables it to spread rapidly. Nimbus, an Omicron subvariant, caused significant disruption in the US over the summer, with a severe sore throat symptom, ominously referred to as “razor blade” throat.
To safeguard against COVID-19 and other respiratory viruses, health professionals recommend maintaining good hygiene, improving indoor air ventilation and filtration, and keeping vaccinations up to date. The CDC’s Advisory Committee on Immunization Practices recently endorsed the 2025-2026 updated COVID vaccines for anyone aged 6 months and older, following consultation with a doctor or pharmacist.