XFG ‘Stratus’ Covid variant on the rise globally: What it is, where it’s spreading and why it matters

A new subvariant of SARS-CoV-2, the virus behind Covid-19, is quietly spreading across the globe and edging closer to becoming dominant. Known as XFG and nicknamed “Stratus”, this subvariant was designated a “variant under monitoring” by the World Health Organisation (WHO) in late June, signalling that it requires close surveillance due to potential public health concerns.

XFG is part of the Omicron family, of which there are now more than 1,000 known subvariants, but it’s rising rapidly in prevalence. According to The Conversation, it was already one of seven variants under monitoring as of June 25. The last to receive this designation before XFG was NB.1.8.1, or “Nimbus” – another cloud-themed nickname.

“A ‘variant under monitoring’ signifies a variant or subvariant which needs prioritised attention and monitoring due to characteristics that may pose an additional threat compared to other circulating variants,” The Conversation explained.

What makes XFG (Stratus) different?

XFG is a recombinant subvariant, meaning it is the result of genetic material shared between two existing variants – LF.7 and LP.8.1.2. Recombinant variants are typically denoted with an “X” prefix.

While recombination isn’t new for Covid-19, it becomes a problem when these genetic changes lead to immune evasion, allowing the virus to dodge vaccine-induced or infection-acquired immunity, which can lead to fresh waves of infection.

“XFG has four key mutations in the spike protein, a protein on the surface of SARS-CoV-2, which allows it to attach to our cells. Some are believed to enhance evasion by certain antibodies,” The Conversation report noted.

Early lab studies have shown that antibodies are almost twice as ineffective in blocking XFG compared to earlier variants like LP.8.1.1.

Where is it spreading?

The earliest sample of XFG was traced back to January 27. As of June 22, a total of 1,648 XFG genome sequences from 38 countries had been submitted to the global database GISAID, which tracks Covid variants.

XFG now makes up 22.7 per cent of all submitted sequences – up sharply from 7.4 per cent just a month prior, and almost overtaking NB.1.8.1, which stood at 24.9 per cent.

According to Australian data expert Mike Honey, India is seeing the highest detection rate, with over 50 per cent of samples showing XFG. Spain follows at 42 per cent, and the US and UK are each reporting XFG in over 30 per cent of cases.

In Australia, XFG is still a small fraction of samples, currently about 5 per cent, but rising.

Is XFG more dangerous?

That remains unclear. As The Conversation reports, scientists are still studying whether XFG causes more severe disease or leads to different symptoms than previous variants.

Some anecdotal reports suggest it may cause “hoarseness” or a scratchy, raspy voice, but experts caution that it’s too soon to say if this is a defining trait.

Crucially, there’s no current evidence that XFG causes more severe illness or is significantly more transmissible than other circulating subvariants.

Will vaccines work against it?

Yes, they’re still expected to work. The most recent Covid vaccine updates were designed against the JN.1 subvariant, and XFG is a descendant of JN.1. So far, the available data shows that approved vaccines remain effective, especially at preventing symptomatic and severe disease.

“Based on the evidence available so far, currently approved Covid vaccines are expected to remain effective against XFG,” The Conversation noted.

That said, waning immunity remains a challenge, and booster doses are strongly recommended, particularly for the elderly and vulnerable groups.

Still, Australia faces low uptake: as of now, only 32.3 per cent of people aged 75 and over have received a vaccine dose in the past six months, and rates are even lower among younger age groups.