A new subvariant of Omicron is "surging" through Europe, an epidemiologist has warned.
The mutation of Omicron BA.1, known as BA.2, was classified by the UK Health Security Agency (UKHSA) as under investigation.
Still, as of January 10, just 53 sequences of the new variant were identified in samples.
The news comes after Ireland moved forward in its reopening plan on Saturday, easing the majority of Covid measures.
However, Eric Feigl-Ding, an epidemiologist and senior fellow at the Federation of American Scientists said that the chance of the BA.2 "displacing" the original variant is "a really bad sign".
Dr Feigl-Ding said data from Denmark suggests "almost half" of Omicron cases in Denmark were BA.2.
In a tweet, he said: "Either it's much faster transmission or it evades immunity even more."
Initial studies from Denmark show no difference in hospitalisations between the original Omicron variant and the new subvariant, and officials believe the vaccine will still be effective against the new subvariant in preventing severe illness.
Dr Feigl-Ding also said data from Germany showed that cases of BA.2 had risen to around 2 per cent of Omicron infections by mid-January, saying "early but looking exponential too."
The frequency of the new variant has also increased In the Netherlands, with statistics suggesting that the proportion has reached five per cent of all Omicron cases.
Dr Feigl-Ding warned that the subvariant appears to be doubling approximately every four days.
He said this is a slower rate of replication than the original Omicron variant, which could displace the Delta variant every 1.5-3 days.
He said: "BA.2 displacing Omicron BA.1 is a really bad sign."
However, Meaghan Kall, lead epidemiologist in the Covid-19 Epidemiology Cell at UKHSA, tweeted: "Yes, BA.2 is increasing in the UK.
"It may have a slight growth advantage, but no evidence at all yet that it can evade Omicron (BA.1) immunity or be different to Omicron in any meaningful way.
"Variants will continue to emerge, but not all variants will be a problem."
The UKHSA said it would be conducting further analysis to understand BA.2 better.
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