What Is the Newest Strain of COVID-19 in Late 2025?
As of late 2025, the newest and most dominant strain of COVID-19 is the XFG variant, nicknamed Stratus. It’s not a single mutation, but a recombinant - a genetic mix of two earlier Omicron subvariants. First widely detected in September 2025, XFG has quickly taken over as the main driver of infections across the UK, the US, and parts of Europe. In the UK, it accounted for nearly 77% of sequenced cases by late September. In the US, Nebraska Medicine reported it made up 85% of cases by October. It’s not the only one, but it’s the one you’re most likely to encounter.
What Makes XFG (Stratus) Different?
XFG doesn’t cause worse illness than earlier strains. That’s the good news. But it spreads faster. Studies from the Netherlands’ RIVM show people infected with XFG report about the same number of symptoms - 7.8 on average - as they did with last year’s KP.3 variant (7.6). The big difference? Sore throat. Eighty-four percent of people with XFG reported a sore throat, up from 71% in 2024. But here’s the catch: it doesn’t feel worse. Virologist Dirk Eggink from RIVM confirmed people didn’t describe it as more painful, just more common.
What’s really driving its spread is how well it binds to human cells. Research from Institut Pasteur shows XFG has low virulence but high efficiency at slipping into cells. That means even people with some immunity from past infections or vaccines can catch it. Still, hospitalization rates haven’t spiked. The UK Health Security Agency and the European Centre for Disease Prevention and Control both say current vaccines still protect well against severe disease, especially for those who’ve had the 2025 Autumn Booster.
The Other Player: NB.1.8.1 (Nimbus)
While XFG dominates, there’s another variant in the mix: NB.1.8.1, nicknamed Nimbus. First spotted in China in January 2025, it’s a hybrid of JN.1 and XBB, evolving from XDV.1.5.1. It’s not as widespread - making up only 7-11% of cases - but it has a signature symptom that stands out.
Clinical reports from Stony Brook Medicine describe a sharp, stabbing pain in the throat, especially when swallowing. It’s not just a sore throat - it’s intense and localized. Patients who’ve had both variants say the difference is noticeable. One Reddit user, u/FluSurvivor2025, wrote: “My Nimbus infection felt like a bad cold with that weird stabbing throat pain - cleared up in 5 days with Paxlovid.”
Nimbus also infects human cells 2.5 times more efficiently than earlier variants, according to lab studies. But here’s the twist: up to 60% of people infected with Nimbus show no symptoms at all. That makes it sneaky. People spread it without knowing, which is why it keeps popping up even as XFG takes over.
How Severe Is It Really?
Let’s cut through the noise: neither XFG nor Nimbus causes more severe disease than previous strains. The data is clear. Hospitalization rates among vaccinated people remain below 1%. For unvaccinated high-risk groups - older adults, people with chronic conditions - it’s higher, around 4.2%, but still lower than the 2022-2023 peak.
Loss of taste, once a hallmark of early COVID, is now less common. Fatigue lasts longer with XFG - 68% of patients on Patient.info reported lingering tiredness for days after the fever broke. With Nimbus, the throat pain lingers 3-4 days, but other symptoms fade faster.
The biggest risk isn’t severity - it’s confusion. Symptoms look like the flu, a cold, or seasonal allergies. One Reddit user, u/MysteryIllness99, said: “Took 3 ATKs before getting a positive - symptoms were identical to my seasonal allergies.” That’s why testing matters. Don’t guess. If you feel off, test.
What Should You Do Now?
If you’re healthy and vaccinated, your risk is low. But here’s what works:
- Get the 2025 Autumn Booster if you’re over 65, immunocompromised, or a healthcare worker. It’s designed to target both XFG and Nimbus spike proteins. Moderna and Pfizer-BioNTech’s updated shots show 87-92% neutralizing antibody response in trials.
- Wear a mask in crowded indoor spaces - especially hospitals, public transit, or during peak flu season.
- Test early. Antigen tests (ATKs) still catch both variants, though you might need to test twice if symptoms are mild.
- Take antivirals like Paxlovid, Molnupiravir, or Remdesivir if you’re high-risk and test positive. Start within 5 days of symptoms.
- Stay home if you’re sick. Even mild cases can spread to vulnerable people.
There are no new lockdowns. No travel bans. No panic. But there’s a shift. COVID-19 is now seasonal, like the flu. The virus keeps evolving, but our tools - vaccines, antivirals, testing - keep up.
What’s Next?
Experts agree: this isn’t the end of the line. Viruses mutate. XFG and Nimbus will likely be replaced by new recombinants in the next 3-6 months. The World Health Organization and ECDC are watching closely, especially in places where immune suppression is common - like areas with limited HIV treatment access. That’s where dangerous new variants could emerge.
For now, the message is simple: stay informed, stay protected, and don’t panic. The newest strain isn’t more deadly. It’s just better at slipping past our defenses. And we’ve learned how to handle that.
Is the new COVID strain more dangerous than before?
No. The newest strains - XFG (Stratus) and NB.1.8.1 (Nimbus) - do not cause more severe illness than previous variants. Hospitalization rates remain low, especially among vaccinated people. The main change is increased transmissibility, not severity.
What are the main symptoms of the latest COVID strain?
The most common symptom across both XFG and Nimbus is a sore throat, reported by 84% of cases. With XFG, it’s a general sore throat. With Nimbus, it’s often described as a sharp, stabbing pain when swallowing. Other symptoms include runny nose, cough, fatigue, and fever. Loss of taste is less common than in earlier variants.
Do vaccines still work against the new strains?
Yes. The 2025 Autumn Booster vaccines were updated to target XFG and NB.1.8.1. Clinical trials show they generate strong antibody responses - 87-92% neutralization - against both variants. They’re especially effective at preventing hospitalization and death, even if you still catch the virus.
Should I get tested if I have a sore throat?
Yes. A sore throat alone could be COVID, the flu, or a cold. Antigen tests (ATKs) are reliable for detecting both XFG and Nimbus, especially if you have other symptoms like fatigue or congestion. If you’re high-risk or live with someone who is, testing helps prevent spread.
Are there any new treatments for these variants?
No new treatments are needed. The same antivirals - Paxlovid, Molnupiravir, and Remdesivir - work just as well against XFG and Nimbus. Timing matters: start within 5 days of symptoms. For high-risk individuals, early treatment reduces hospitalization risk by up to 80%.
How long does the new strain last?
Most people recover in 5-7 days with rest and hydration. The sore throat from Nimbus can last 3-4 days. Fatigue from XFG may linger for a week or more. If symptoms worsen after day 5 - like shortness of breath or chest pain - seek medical help.
Can you get infected with both strains at once?
It’s possible but rare. The immune system usually responds to one variant before another can take hold. Most cases are caused by a single dominant strain. Genetic sequencing shows co-infections are under 1% of total cases.
Is there a risk of long COVID with these new strains?
Yes, but the risk hasn’t increased. Long COVID still affects about 5-10% of infected people, regardless of the variant. Fatigue, brain fog, and shortness of breath are the most common long-term symptoms. Vaccination reduces the risk by about 50%.
Bottom Line
The newest strain isn’t a monster. It’s just smarter at spreading. XFG is the main one right now, with Nimbus hanging on in the background. Neither is worse than what we’ve seen before. What matters now isn’t fear - it’s preparedness. Get your booster. Test when you feel off. Treat early if you’re at risk. And remember: we’ve done this before. We know how to handle it.
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