The first cases of a new Covid-19 variant of concern have been confirmed in Ireland.
The two cases of BA.4 were detected here earlier this month.
They were identified from whole genome sequencing carried out on a proportion of confirmed virus cases during the week of 7 May.
BA.4 is a sub-lineage of the highly transmissible Omicron, which is currently the dominant strain of Covid in Ireland.
The European Centre for Disease Prevention and Control reclassified BA.4 and another sub-lineage of Omicron, BA.5, from variants of interest to variants of concern on 12 May.
They were first detected in South Africa in January and February of this year, where they have become dominant.
'No indication of any change in severity'
The ECDC said the growth advantage of the two strains "is likely due to their ability to evade immune protection induced by prior infection and/or vaccination, particularly if this has waned over time".
It also said: "there is currently no indication of any change in severity for BA.4 or BA.5 compared to previous Omicron lineages."
The overall proportion of the two strains in Europe is currently low.
However, the ECDC said: "the presence of these variants could cause a significant overall increase in Covid-19 cases in the EU/EEA in the coming weeks and months" and based on the high growth rates reported, it expects they will become the dominant sub-lineages.
The two BA.4 cases in Ireland were confirmed in the weekly letter from the Chief Medical Officer to the Minister for Health Stephen Donnelly on 13 May.
No cases of BA.5 had been detected here as of that date.
Dr Tony Holohan said: "the overall epidemiological situation in Ireland currently provides a broadly positive outlook, albeit we will need to continue to monitor developments with emerging variants over the coming weeks."