A newly detected COVID-19 variant known as NB.1.8.1 has made its way to the U.S., raising questions about whether it could fuel another summer surge in cases. While experts emphasize that it’s too early to draw firm conclusions, health authorities are closely watching the situation.

Here’s what you need to know about this emerging variant, including its symptoms, spread, and whether current vaccines still offer protection.

What Is NB.1.8.1?

NB.1.8.1 is a descendant of the Omicron JN.1 lineage and was first identified in January 2025. It’s considered a “variant under monitoring” by the World Health Organization (WHO)—a category used for variants with potential public health implications but not yet deemed highly dangerous.

The variant is genetically distinct from the currently dominant U.S. strain, LP.8.1, and has seen a rapid increase globally. From April 21 to April 27, NB.1.8.1 accounted for 10.7% of sequenced COVID cases worldwide, up from just 2.5% a month earlier.

Where Has NB.1.8.1 Been Found?

As of late May, fewer than 20 sequences of NB.1.8.1 had been detected in the United States. However, cases have been identified among international travelers arriving at airports in California, New York City, Virginia, and Washington State.

Globally, the variant is spreading rapidly in China and Hong Kong, and has now been confirmed in 22 countries.

What Are the Symptoms of NB.1.8.1?

So far, the symptoms of NB.1.8.1 appear similar to those of previous COVID variants, including:

  • Fever or chills

  • Cough

  • Sore throat

  • Nasal congestion

  • Fatigue

  • Difficulty breathing

  • Diarrhea

There is no evidence that NB.1.8.1 causes more severe illness than previous Omicron-related strains. In fact, most people can expect mild to moderate symptoms, especially if they’re vaccinated or previously infected.

Could NB.1.8.1 Lead to a Summer COVID Surge?

Experts say that while NB.1.8.1 currently represents only a small fraction of U.S. cases, its characteristics make it worth watching.

The variant carries six mutations on the spike protein, which may help it spread more easily and partially evade immunity from vaccines or prior infection. That said, no single mutation appears dangerous enough on its own to trigger a major wave.

However, seasonal trends suggest a summer spike is possible—whether from NB.1.8.1 or another variant.

“Unlike the flu, which usually peaks once in winter, COVID has shown two peaks annually—one in summer, and another in winter,” said Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center.

Do Current Vaccines Protect Against NB.1.8.1?

According to experts, existing vaccines and prior infections are still likely to offer some protection, especially against severe illness and hospitalization.

Additionally, new updated COVID booster shots from Pfizer, Moderna, and Novavax are expected to launch in early fall 2025. While it’s unclear which formula the FDA will recommend, early data suggests these new vaccines will offer broad coverage, including against NB.1.8.1.

“It’s hard to say how effective future vaccines will be until we know what formulation is approved,” said Dr. Amy Edwards, infectious disease specialist at Case Western Reserve University. “But current immunity should still provide partial defense.”

How to Stay Safe This Summer

Even though NB.1.8.1 is not currently causing widespread concern, experts stress the importance of basic precautions—especially for high-risk individuals, such as older adults and people with underlying health conditions.

Here are steps to protect yourself and others:

  • Wash your hands frequently

  • Wear a mask in crowded indoor spaces or when traveling

  • Stay home if you feel unwell

  • Cover your coughs and sneezes properly

  • Monitor local COVID trends and stay informed

“COVID isn’t gone—it’s still killing hundreds of Americans each week,” Schaffner added. “We have to continue living with it while taking reasonable steps to stay safe.”

The Bottom Line

The NB.1.8.1 variant is spreading globally and has now reached the U.S., prompting health officials to label it a variant under monitoring. While it may be more transmissible, it doesn’t appear more severe, and vaccines likely offer some level of protection.

Whether or not it triggers a summer surge, experts agree: maintaining basic hygiene and staying up to date on vaccines remains key to reducing risk.