Forty per cent of new Covid-19 cases here are believed to involve a more transmissible and possibly more severe sub-variant of Omicron, according to chief medical officer Dr Tony Holohan.
The BA.2 sub-lineage of Omicron, which is growing at almost 10 per cent a day, is expected to become dominant in the Republic by the end of the month, he said in his latest letter to Government.
It is already dominant in Northern Ireland, according to data published this week by UK public health authorities.
New research suggests BA.2 may cause more severe disease and is more effective in evading some of the existing protections against Covid-19.
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The study from Japan, which has not been peer reviewed, found it may be as capable of causing serious illness as previous variants, such as Delta.
As well as evading vaccine immunity, it is resistant to some treatments, such as the monoclonal antibody sotrovimab, according to the lab study.
BA.2 cannot be identified without genomic sequencing of cases, but its growth can be estimated by the declining percentage of current infections that are S-gene target negative in a PCR test. The Omicron variant is S-gene target negative in tests, but the proportion of such results has declined from almost 100 per cent to 60 per cent in recent weeks as BA.2 has advanced.
Some experts have called for BA.2, which is up to 50 per cent more contagious than Omicron, to be designated as a separate variant of concern.
In his letter, Dr Holohan warns that the pandemic is not over, that levels of infection remain high and that a cohort of the population remain vulnerable to the emergence of new variants with increased transmissibility, immune escape and/or virulence.
