The U.S. Centers for Disease Control and Prevention (CDC) has revealed that there has been an increase in people infected with a new strain of Covid-19, known as NB.1.8.1.
According to the health body, 37% of Covid-19 cases recorded in the first few weeks of June 2025 in the US came from the strain - a 15% increase from the two weeks before.
Reports from around the world also note an increase in cases of the new ‘Ninbus’ strain, which is thought to be more transmissible than previous variants.
However, it’s thought that the number of cases could be higher than reported as the sequencing data used to track new variants isn’t thought to be accurate enough.
In recent days, India has also recorded instances of the new strain, alongside Thailand, China and Indonesia. Several cases were also detected in the UK at the start of this month.
The strain was initially discovered in the United States in late March and early April in foreign visitors arriving at airports in New York, California, Washington State, and Virginia. Since then, further cases have surfaced in Hawaii, Rhode Island, and Ohio.
Experts are concerned about the variant's quick spread in China and other parts of Asia, where it has already surpassed the prevalent strain, even though the number of confirmed cases in the US is still low.
According to the New York Post, health officials in Hong Kong recorded a notable increase in Covid-related hospitalisations and ER visits during the previous month, particularly among the elderly.
But what is NB.1.8.1. and should we be worried?
What is the new Covid variant?
According to the World Health Organisation (WHO), NB.1.8.1 is a SARS-CoV-2 strain that is being monitored and is becoming more prevalent worldwide. The agency is now tracking six of them.
The WHO reports that the first detection of NB.1.8.1 was made from samples taken in January 2025. It descends from the recombinant XDV lineage and is a sublineage of the Omicron variety.
Recombinant refers to the creation of a new variety through the genetic blending of two or more pre-existing variants.
The Covid vaccines that are currently authorised should continue to be effective against this variation and provide protection against serious illness.
While NB.1.8.1 does not seem to cause more severe sickness, it is spreading more quickly than previous variations, according to Dr Amy Edwards of Case Western Reserve University, who spoke to CBS News. “What they're seeing in China, Hong Kong, and elsewhere is a sharp uptick in hospitalisations”, she stated.
The variation was discovered as US health organisations updated their recommendations for the Covid-19 vaccine.
The CDC declared that booster doses will from now on only be administered to those at greatest risk, such as the elderly, and that it will no longer advise routine immunisation for healthy young people and pregnant women.
Although the WHO is tracking the new strain, that doesn’t necessarily mean that people should be worried that we’re heading into another pandemic. Monitoring means that health experts can keep on top of data and act fast if a surge continues.
What are the symptoms?
The new strain's symptoms, which include fever, sore throat, cough and fatigue, are the same as earlier variations.
Gastrointestinal symptoms may also be seen in some cases.
According to specialists like Dr Subhash Verma of the University of Nevada, NB.1.8.1 seems to have a “growth advantage” that makes it easier to spread.
Where is it spreading?
As of early June, the variant has been detected in 22 different nations, according to the World Health Network. It has been linked to New York, California, Arizona, Ohio, and Rhode Island in the United States, according to documents from local health officials at Ginkgo Bioworks, CDC's airport testing partner.
The WHO reported a notable increase in its incidence from late March to April, although the numbers were still small.
In just four weeks, Hong Kong reported 81 severe cases and 30 deaths associated with the variation, the majority of which involved individuals 65 years of age and older.
India has recorded over 1,000 cases of the new Covid-19 strain.
In mainland China, the number of hospitalisations and the proportion of ER patients who test positive for Covid has more than doubled in recent weeks.
Chinese authorities have downplayed the variant's seriousness despite the surge, claiming it is not more harmful than earlier strains. However, US health authorities are still wary.
