Ireland's Chief Medical Officer Tony Holohan is in hospital undergoing tests.
However he told RTÉ that it is unrelated to the COVID-19 coronavirus.
The Deputy Chief Medical Offier at the Department of Health, Dr Ronan Glynn, is expected to take over until his release on Thursday.
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Dr Holohan has held regular media briefings about coronavirus over the past month.
He appeared unwell during a briefing on Tuesday.
He then went to St James's Hospital in Dublin for treatment.