DUBLIN, Dec 13 (Reuters) - The Omicron variant likely accounts for 11% of new COVID-19 cases in Ireland, its health chiefs said on Monday, predicting a very rapid increase in the proportion of Omicron infections in the coming days amid probable widespread community transmission. Ireland has so far confirmed 18 cases of the variant through whole-genome sequencing out of an average 4,000 COVID-19 cases it has been reporting each day. A trait distinguishing Omicron from the dominant Delta variant suggests a much higher total, said the National Public Health Emergency Team. "Using this methodology, we estimate that 11% of cases are now due to the Omicron variant, an increase from less than 1% only one week ago," Ireland"s Chief Medical Officer Tony Holohan said in a statement. Just over 90% of Ireland"s eligible 3.9 million people over the age of 12 have been fully vaccinated - one of the highest rates of protection in Europe - and it has administered a further 1.2 million booster doses. The government, which has shut nightclubs and placed limits on the capacity and opening hours of bars, restaurants and indoor events, has promised to speed up the booster campaign this week. It will also cut the gap between completion of the primary schedule of COVID-19 vaccination and a booster dose to three months from five months, Health Minister Stephen Donnelly said on Monday, While the number of COVID-19 infections have stabilised at near-record levels in recent weeks, the proportion of people testing positive is falling gradually, along with the numbers in hospital and in need of critical care.