The seven-day average of Covid-19 cases has increased by 77% in the past three weeks.
It now stands at 2,612 - compared to 1,477 on October 13th.
NPHET says the future is 'very uncertain' and is urging people to reduce their social contacts immediately.
But Dr Gerald Barry, an assistant professor of virology in UCD, believes cases will continue to rise sharply this month.
"As more and more people become actively infected and actively shedding virus, and there is limited pause on that socialisation and no increase in other mitigations to stop that then inevitably we're going to see a rapidly rising number of cases in the short term I would suggest.
