Associate Professor of Biochemistry at Trinity College Dublin Tomás Ryan has said the situation with Covid-19 has got worse since Sunday and despite two weeks of Level 3 restrictions in Dublin, we still have "what looks like exponential growth".
Dr Ryan said that NPHET's call for Level 5 restrictions to be applied was justified and the Government should have put them in place on Monday.
He said that from the day the Government's Framework for Restrictive Measures was published there should have been contingency plans at every economic level that would allow the Government to act on a day's notice, subject to recommendations from the National Public Health Emergency Team (NPHET).
The virus does not take weekends off, he said.
The latest data shows that Ireland's 14-day incidence rate per 100,000 of population is 124.
Donegal remains the county with the highest number of cases per 100,000, at 312. Another border county, Monaghan, is the second highest at 257.4, which is still far higher than Dublin at 171.4.
Seven other counties have 14-day incidence rates above 100: Roscommon (170.4), Clare (157.4), Cavan (144.4), Cork (118.8), Limerick (107.7), and Offaly (105.2).
This data is measured by the Health Protection Surveillance Centre and takes account of the 5,925 new cases recorded between 23 September and 6 October.
Dr Ryan told RTÉ's Today with Claire Byrne that restrictions are there to guide people's behaviour and if everyone really minimised their contacts and followed all the public health advice, transmission of Covid-19 would reduce.
However, he added, the reality is that many people have a great deal of expectations in terms of normality and their social, economic lives and Level 3 restrictions are not having enough of an effect in Dublin.
Dr Ryan said the situation has got worse since Sunday and, despite two weeks of Level 3 in Dublin, we still have "what looks like exponential growth".
If we wait another two weeks to go to Level 5, he said, by conservative modeling we could be looking at around 1,500 cases a day.
Dr Ryan said the UK does seem to be ahead of us in their second wave and it would be ideal to have an all-Ireland approach, as has happened in the past in animal health.
While this would be optimum, he said, we cannot afford to wait for Northern Ireland and we need to act in the interests of the Republic.
Dr Ryan added that having a localised approach would help, and if we do go to Level 5, then it is possible that areas such as Kerry or Mayo, where there are a low number of cases, may not need such strict measures.
He said that there has been steady exponential growth since mid-summer and nothing is contributing to its suppression so we need a change of strategy.
There are 159 patients with Covid-19 in hospital as of 8am today. At 8pm yesterday, that number was 155.
Seventeen people have been admitted to hospital in the last 24 hours, while 12 people were discharged.
Twenty-seven people with the virus are in intensive care. There have been three people admitted to ICU in the last 24 hours, and one person discharged.
Figures from the Health Service Executive show that as of 8pm yesterday, there were 28 critical care beds available.
There are 248 critical care beds currently occupied by non-Covid and Covid-19 (27) patients.
More than 1,400 new cases of the coronavirus were reported on the island yesterday, with 828 in Northern Ireland and 611 in the Republic.
Green Party Leader and Minister for Climate Action and Communication Networks Eamon Ryan has said he favours waiting two weeks before looking again at the Covid-19 restriction level.
Mr Ryan said the expert advice has always been that it takes that long to see the effect of changing restrictions, but he added if there is new information or circumstances change then it can be looked at again before then.
Minister for Community and Rural Development Heather Humphreys said if people take individual action to cut down on contacts and take precautions then Covid-19 can be stopped.
Mr Ryan later told RTÉ's Today with Claire Byrne that the Government will continue to listen to expert public health advice and be guided by it.
He added that no one can be certain on the virus and nothing can be ruled out.
However, Nr Ryan said that even if the country was moved to Level 5, it would have to be asked if the process would have to be repeated in the future, which would have a huge effect on people's mental and economic health.
He said we should try to match other European countries who have not gone into full lockdown, but have managed to keep cases at a lower level.