NB.1.8.1 'Nimbus' Variant Now Dominant in U.S.

Just as the summer season kicks off, a new COVID-19 strain is making the rounds across the nation – and fast. The NB.1.8.1 variant, known by its nickname “Nimbus,” is now responsible for roughly 37% of COVID-19 cases nationwide. 

If you haven’t heard of it yet, you’re not alone. But, it’s spreading quickly, and experts are keeping a close watch.

Here’s what we know so far about this fast-moving Omicron offshoot, from symptoms to vaccine effectiveness, and what you can do to stay protected.

COVID-19 'Nimbus' Variant: Rising Cases and Key Symptoms

The Omnicron subvariant NB.1.8.1, or “Nimbus,” is a mutated form of Omicron that’s now one of the most common COVID-19 strains in the U.S. It was first detected through airport screenings in late March and has since been found in at least 13 states, including California, New York, Illinois, and Hawaii.

While it hasn’t officially taken the top spot just yet (that title currently belongs to LP.8.1), Nimbus is right behind it and gaining ground fast. In early June, it was responsible for more than a third of the cases in the U.S., making it the second-most common COVID strain in the country.

The nickname “Nimbus” was coined on social media by Canadian evolutionary biologist T. Ryan Gregory, who’s also behind names like the “FLiRT” variants. It’s not an official scientific name, but it’s certainly catching on.

What Are the Symptoms of the Nimbus COVID Strain?

So far, COVID-19's 'Nimbus' symptoms look pretty similar to what we’ve seen with other Omicron variants. If you’ve had COVID in the last year or two, you’ll probably recognize these:

• Sore throat

• Cough

• Runny nose or congestion

• Shortness of breath

• Fever or chills

• Headache

• Muscle or body aches

• Fatigue

• Loss of taste or smell

For most people, the new COVID variant symptoms are mild to moderate. But, folks over 65, immunocompromised people, and those with underlying conditions still face a higher risk of serious illness.

Is the NB.1.8.1 Variant More Contagious?

Possibly, but the jury’s still out. The Nimbus COVID strain has several mutations in its spike protein, which may make it better at attaching to human cells. That could explain why it’s spreading so quickly.

While some early lab data (not yet peer-reviewed) suggests it might be more transmissible than other strains, there’s no evidence yet that it causes more severe illness. 

The World Health Organization has labeled it a “variant under monitoring,” meaning they’re watching it closely but don’t consider it a major threat right now.

Still, with travel picking up and people gathering indoors to escape summer heat, any highly contagious variant can gain traction quickly.

How Widespread Is Nimbus in the U.S.?

The NB.1.8.1 variant has been reported in at least 13 U.S. states so far:

• Arizona

• California

• New Jersey

• New York

• Hawaii

• Illinois

• Maryland

• Massachusetts

• Ohio

• Rhode Island

• Vermont

• Virginia

• Washington

Given how easily this strain spreads, it’s may already be present in other states. It just hasn’t officially been tracked everywhere yet.

Will We See a Summer COVID Surge?

Possibly, but it might not be a big one. The U.S. is said to have pretty high levels of population immunity – around 90% of people have been exposed to COVID through infection or vaccination. That helps block major waves.

However, immunity does fade over time. The further we get from past vaccinations or infections, the more we’re susceptible. And, with a highly mutated strain like NB.1.8.1 in circulation, there’s definitely potential for more infections.

Historically, COVID tends to surge in the U.S. twice a year: once in winter, and again in summer. So, we may see a bump in cases over the next few months. But, hopefully, it will be smaller than the waves we saw before 2023.

Are Vaccines Effective Against NB.1.8.1?

So far, vaccines still do a good job of preventing severe illness, hospitalizations, and death, even with newer variants like Nimbus. However, because this strain carries immune-evasive mutations, protection against infection may be lower, especially for those who haven’t had a booster recently.

The 2024-2025 COVID-19 vaccines are still available and recommended for most adults over 18. If it’s been more than six months since your last dose or if you’re in a high-risk group, it’s worth considering a booster.

Looking ahead, new 2025-2026 COVID vaccines are expected this fall. These will target the LP.8.1 variant but may still offer some cross-protection against Nimbus. That said, new federal guidelines mean the fall boosters will be limited to:

• Adults 65 and older

• People ages 12-64 with at least one underlying condition

Healthy kids and pregnant women are no longer routinely recommended for COVID vaccination under current CDC guidance, though many doctors still advise it. If you’re unsure, it’s best to check with your healthcare provider.

How to Protect Yourself From the Nimbus Variant

The basics still apply, even for the COVID-19 variant in 2025:

• Test if you have symptoms.

• Stay home when sick.

• Wear a mask in crowded indoor spaces.

• Keep some distance in high-risk settings.

While the federal program for free test kits has ended, you can still find affordable or insurance-covered tests at pharmacies and clinics.

What to Know About the NB.1.8.1 Variant Going Forward

While the NB.1.8.1 variant, a.k.a. Nimbus, isn’t something to panic about, it’s definitely something to watch. It’s spreading quickly, has some tricky mutations, and may play a role in a summer increase in COVID cases. But, thanks to high immunity levels and updated vaccines, the overall risk to most people remains low.

Staying informed, being cautious, and keeping up with vaccine recommendations are still the best ways to ride out whatever this virus throws at us next. Stay safe, stay smart, and enjoy your summer.