A new Covid-19 strain is fast spreading throughout Australia with doctors again urging people to access booster vaccinations.

The Covid strain NB.1.8.1 has been designated by the World Health Organisation as a “variant under monitoring”.

NB.1.8.1 currently makes up more than 40 per cent of all total Covid cases tested in Victoria, about 25 per cent in Western Australia and NSW, 20 per cent in Queensland and less than 10 per cent in South Australia.

“The new strain is now the dominant coronavirus strain in China and Hong Kong and, in Australia, we’re seeing it pretty much everywhere,” Griffith University virologist Associate Professor Lara Herrero said.

Herrato told the ABC the strain was predicted to become the dominant Covid varient in Australia too. 

“We’re seeing a lot of cases in the community coming through the [emergency department] but it’s likely we’re heavily under-reporting because Covid reporting is no longer mandatory,”  she said.

The task of tracking NB.1.8.1 and its impact is more difficult than in the days of the pandemic as fewer people are testing and reporting infections.

So what do we need to know about this fast-spreading Covid variant?

Where does it come from?

According to the WHO, NB.1.8.1 was first detected in samples collected in January 2025.

It’s a ‘sublineage’ of the Omicron variant, and is thought to be a strain arising from the genetic mixing of two or more existing variants.

Herraro said while not much data was available yet for this variant, a recent preprint (a study that has not yet been peer reviewed) offered clues about why NB.1.8.1 may be gathering traction.

“Using lab-based models, researchers found NB.1.8.1 had the strongest binding affinity to the human ACE2 receptor of several variants tested – suggesting it may infect cells more efficiently than earlier strains,” she said.

The study also found that it was possible a person infected with NB.1.8.1 may be more likely to pass the virus on to someone else, compared to earlier variants.

How dangerous is it

The good news is that while it may spread faster and more easily within the community, the WHO has not yet observed any evidence it causes more severe disease compared to other variants.

“Reports suggest symptoms of NB.1.8.1 should align closely with other Omicron subvariants,” Herrara said..

Common symptoms include sore throat, fatigue, fever, mild cough, muscle aches and nasal congestion. Some people may also have gastrointestinal symptoms.

Is there a vaccine?

Herrero said the most recent booster available in Australia and many other countries targeted the JN.1 varient, from which NB.1.8.1 was descended.

“So it makes sense it should still offer good protection,” she said.

Unfortunately only 6.6 per cent of adults have received a Covid vaccine in the past six months, according to federal data. 

Health Minister Mark Butler has encouraged Australians to get the Covid booster as winter officially begins

“I do encourage, particularly as we head into winter, for people to think about the last time they got a Covid vaccine,”  Butler said.

“Older Australians are strongly encouraged and recommended to get that booster. But certainly everyone else is eligible for a free Covid booster, if they’ve not had one in the last 12 months at their local pharmacy or GP.”

Will it gets worse over winter?

Australian Medical Association NSW chair of public health Dr Michael Bonning said respiratory infections were generally up nationally. 

“We are expecting a spike in cases over the coming weeks with an expectation of a particularly difficult winter respiratory season because of what we have seen in the northern hemisphere,” he told the ABC.

Just 6.6 per cent of adults had a Covid vaccine in the past six months. Photo: Getty

“In NSW in the past week there was an increase of 29.2 per cent in Covid-19 notifications, an increase of 25.9 per cent in influenza notifications, and an increase of 9.7 per cent in RSV notifications,” Bonning said.