Everything you need to know about the so-called ‘American COVID’ variant
The XFG variant has been circulating for more than a year and is currently the most common form of SARS-CoV-2 globally.
- 19 October 2026
- 3 min read
- by Linda Geddes
At a glance
- Recent media headlines have drawn attention to a SARS-CoV-2 variant known as XFG, which now accounts for nearly half of sequenced samples worldwide.
- XFG has been circulating since at least January 2025, and is designated a ‘variant under monitoring’, meaning it has genetic changes suspected to affect its behaviour. However, there’s currently no evidence that it leads to more severe illness than other COVID-19 variants.
- Laboratory studies suggest that COVID-19 vaccines continue to generate immune responses against XFG.
Headlines have been ringing alarm bells in recent weeks about a subvariant of COVID-19 dubbed ‘American COVID’.
The virus they’re referring to is a form of SARS-CoV-2 that is officially known as XFG, although it’s also been nicknamed ‘Stratus’, referencing a type of cloud.
It was first detected in January 2025, and by June of that year it already accounted for around 17% of sequenced COVID-19 samples in Europe, more than a quarter in the Americas and as many as 69% in South-East Asia, although relatively few samples were sequenced there.
It is unclear why XFG has earned the moniker ‘American COVID’. Possibly it is because by October 2025, XFG accounted for roughly 70% of sequenced samples in the US, although it has since been overtaken by newer variants, including some of its own descendants.
Globally, however, XFG is currently the most prevalent variant, accounting for around 49% of sequenced samples shared with the international GISAID database in the week ending 13 September 2026, according to the World Health Organization (WHO).
How does XFG differ from previous COVID variants?
XFG is a subvariant of the Omicron variant, which has accounted for almost all COVID-19 infections since 2022. However, it carries several mutations in its spike protein that help it evade antibodies generated by previous infections or vaccination.
Laboratory studies suggest that it may be better at doing so than some earlier variants, potentially helping to explain its global spread. However, it binds less strongly to the ACE2 receptor that the virus uses to enter human cells.
WHO designated XFG a ‘variant under monitoring’ in June 2025, meaning it has genetic changes suspected to affect characteristics such as how easily it spreads between people or its ability to evade immunity.
However, there’s currently no evidence that it leads to more severe illness than other SARS-CoV-2 variants in circulation.
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How well do current vaccines protect against it?
Laboratory studies suggest that COVID-19 vaccines targeting earlier Omicron variants continue to generate immune responses against XFG.
At its most recent meeting in May 2026, WHO’s Technical Advisory Group on COVID-19 Vaccine Composition recommended that manufacturers continue to use an earlier Omicron subvariant called LP.8.1 as the basis for updated COVID-19 vaccines, citing evidence that these vaccines boost antibodies capable of neutralising XFG and other circulating variants such as NB.1.8.1 (nicknamed ‘Nimbus’) and JN.1 (nicknamed ‘Juno’).
However, it said that other vaccines based on XFG and NB.1.8.1 could also be used.
Although COVID-19 vaccines don’t reliably prevent infection with the virus, they remain one of our best defences against severe disease and hospitalisation.
“Member States should consider routine COVID-19 vaccination of groups at highest risk of severe COVID-19 disease and vaccination should not be delayed in anticipation of access to vaccines with an updated antigen composition,” WHO said.
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