NPHET's Professor Philip Nolan has warned of an "uptick in Dublin" of Covid-19 among the younger population.
The public health expert said cases among 18-34 year olds have increased 50-70% in just a few days, calling it "the first sign of Omicron spreading rapidly".
Professor Nolan added that test positivity among 19-24 year olds "exceeds 25%" and there is "an uptick" in the capital.
He urged the public to follow "risk reduction" guidelines to limit the spread of the disease.
He said on Twitter today: "We need to prevent onward transmission, especially to the vulnerable.
"Stay home if symptomatic and seek a test. Restrict movements and follow the testing regimen if a close contact.
"Do not run the risk of infecting those you love. If you have no symptoms or restrictions, prioritise and limit your contacts, and reduce the risk of those contacts.
"Risk reduction: Consider meeting outdoors, shorten time, avoid crowds and crowded spaces, ensure adequate ventilation, maintain physical distance, wear a mask, good hand hygiene.
"If you are meeting vulnerable people, all the above and consider serial antigen testing."
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