The XEC strain, which is believed to be more transmissible, has shown up in 7.1pc of virus samples analysed here.
It first appeared in Germany in June and is spreading rapidly throughout other parts of Europe.
It is a sub-variant of the Omicron strain and a recombinant strain, which is a hybrid of sub-lineages KP.3.3 and KS.1.1.
The World Health Organisation is monitoring it, but there is no indication that it is more severe and symptoms of infection have not changed.
It has been blamed for contributing to a rise in infection in hospital patients in parts of the UK, but the most up-to-date reports on Ireland are not showing that trend.
There were 140 patients with the virus in Irish hospitals yesterday, but the majority are there for other illnesses.
There were 176 patients in hospital with the virus two weeks ago.
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Eleven patients with the virus were in intensive care units yesterday, the same number as a fortnight ago, and the overall positivity rate is stable at around 9.7pc.
In the first week of this month, the Health Protection Surveillance Centre (HPSC) said Covid activity was at moderate levels and continued to decline, while deaths remained low.
There were three outbreaks in nursing homes and 14 in hospitals during that week.
Covid vaccinations are currently being offered by the HSE and the current jab is believed to offer good protection against the new strain.
It is available for free to people aged 60 and older, people living in long-term facilities, those with weakened immune systems, healthcare workers and pregnant women.
People outside those groups can also discuss getting a vaccine with their GP or pharmacist.
The likelihood of getting very sick after infection is still highest for at-risk groups.
The HSE is currently reviewing whether it will reimburse doctors and hospitals for the anti-viral Paxlovid, which has been given to vulnerable patients who caught Covid and could be at risk of hospitalisation or admission to intensive care.
The uptake of Covid booster vaccines remains low. In recent weeks, it was highest among people aged over 80, at 26.9pc, followed by people aged in their 70s, at 20.7pc.
Respiratory syncytial virus (RSV) cases, meanwhile, rose tenfold in the first week of the month, but numbers remain low. There were 19 cases, 13 hospitalisations, zero intensive care cases and no deaths reported.
The highest notification and hospitalisation rates were in infants under one year old, the HPSC said.
A jab to protect babies from getting very sick from RSV is now available to all newborns in maternity hospitals.
Overall, flu was at low levels early this month, but there has been a consistent increase since last month. The highest rates were in the over-80s.