A second case of the Omicron variant has been confirmed in Ireland.
No further details of the case - such as whether it was travel-related - have yet been confirmed.
Studies have suggested Omicron is more transmissible than other COVID-19 strains, and a booster may be needed for full protection.
HSE chief clinical officer, Dr Colm Henry, says it is likely more cases will be confirmed in the coming weeks.
"I've no doubt there will be further cases, no doubt.
"There is a marker for this, but it's not absolutely specific - that's the S gene dropout.
"And at this point in time, quite a number of S gene dropouts are being investigated and being sequenced.
"I've no doubt many of those will be confirmed as Omicron cases".
He was speaking as 4,022 further cases of COVID-19 were confirmed here on Thursday.
The Department of Health says there are now a total of six cases of the Omicron variant in Ireland.
Chief Medical Officer Dr Tony Holohan says more Omicron-suspected cases are being investigated.
"There are now six confirmed cases of the Omicron variant in Ireland.
"A number of other probable cases are under investigation.
"Although this is a new variant, our early understanding gives us confidence that a booster dose of COVID-19 vaccine will offer good protection against Omicron and Delta infection."