We have entered cold and flu season, and two new variants of COVID are doing the rounds: Nimbus and Stratus. While they each have a few tricky mutations that allow them to spread more quickly and easily than some earlier variants, there is no evidence that they are any more severe than those previous.
How These COVID Strains are Different
For the most part, symptoms are similar to those of previous iterations of COVID-19: fever or chills, cough, sore throat, runny nose, fatigue, body aches, and digestive symptoms, such as nausea or diarrhea.
According to Stony Brook Medicine, many of those who have contracted the Nimbus variant (NB.1.8.1 ) have also reported a distinctive “sharp, stabbing sore throat” that is particularly noticeable when swallowing. Some individuals have also reported experiencing a hoarse or croaky voice.
Aside from symptoms, these new variants possess specific mutations that make them more transmissible, essentially enabling them to pass from person to person more easily and hence, more quickly. In Nimbus’ case, the mutations enable the virus to bind to human cells more efficiently. Specifically, it helps it attach to a protein called the ACE2 receptor, which is the point at which all variants of COVID-19 use to enter the cell, much like a door to a house.
In contrast, the mutations identified in Stratus (XFG) don’t help the virus bind to the cell any more easily than previous variants but do allow it to evade the antibodies designed to ward off infection more easily.
Read More: COVID Infection Can Age Blood Vessels and Weaken Heart Health, Especially in Women
How Quickly Are The New Variants Spreading?
According to the World Health Organization (WHO), the earliest samples of both variants were collected in January 2025. Since then, they have overtaken earlier iterations of COVID-19 to become the dominant variants in the U.S.
Projected estimates published by the Centers for Disease Control and Prevention (CDC) suggest that Stratus currently accounts for approximately 85 percent of COVID-19 cases, and Nimbus accounts for a further 7 percent. Meanwhile, the XEC and KP3.1.1 variants, which dominated at the start of the year, currently make up less than 1 percent of current cases.
Why Do New Variants Keep Popping Up?
As with the flu, COVID-19 is constantly evolving and mutating, resulting in a steady stream of new variants. These mutations occur in the virus’s genetic sequence and can result in different traits and characteristics.
When these alterations offer an evolutionary advantage — by enabling the virus to enter cells more efficiently or evade detection by the immune system, for example — it allows new variants to dominate, as we are seeing with Nimbus and Stratus. Both are themselves subvariants of Omicron, which first emerged in 2021 but no longer exists in its original form.
As per the CDC: “New variants of SARS-CoV-2 are expected to continue to emerge. Some variants will emerge and disappear, while others will emerge and continue to spread and may replace previous variants.”
How To Prepare For This Year’s Cold, Flu, And Covid-19 Season
The CDC continues to advise regular COVID-19 vaccines. While these don’t necessarily prevent you from contracting the disease, they do reduce the risk of more severe symptoms and hospitalization. Practicing good hygiene and cleanliness, and ventilating indoor spaces are additional steps that can be taken to reduce the risk of catching COVID in the first place.
If sick, the CDC recommends taking precautions to limit the spread of the disease. This includes staying at home and avoiding others if you are symptomatic.
The CDC advises: “Seek health care promptly for testing and/or treatment if you have risk factors for severe illness. Treatment may help lower your risk of severe illness, but it needs to be started within a few days of when your symptoms begin.”
This article is not offering medical advice and should be used for informational purposes only.
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- CDC. Variants and Genomic Surveillance
- CDC. How to protect yourself and others
- Stony Brook Medicine. Understanding COVID Nimbus: Symptoms and Key Facts
- WHO. WHO TAG-VE Risk Evaluation for SARS-CoV-2 Variant Under Monitoring: NB.1.8.1
- WHO. WHO TAG-VE Risk Evaluation for SARS-CoV-2 Variant Under Monitoring: XFG.
