Dr Philip Nolan, chair of the National Public Health Emergency Team (NPHET) modelling advisory group, says the three counties under lockdown are experiencing new infections at several multiples of the national average.
The Health Protection Surveillance Centre (HPSC) confirmed yesterday that 174 people have tested positive for Covid-19 in the latest official data.
Of these cases, 110 were recorded in Kildare while seven were recorded in Offaly and one in Laois.
It is the largest number of confirmed cases reported in Ireland in one day since May and brings the total number infected to date in Ireland to over 26,600.
Another patient infected with the virus has also died.
Speaking about the rate of new infections in the three lockdown counties, Dr Nolan said the national average is 16.3 per 100,000 population.
"Kildare is at 130 so that is close to seven times the national average. Laois is at 70 per 100,000 and Offaly is at 90 per 100,000.
"Looking across the Dublin region where you have a much higher population, you are looking at a rate much closer to 10.
"Should these cases result in widespread transmission, it could undo a lot of the good work that we have done as a country so far to control the spread of this virus.
"The measures introduced by NPHET represent a proactive and proportionate response to the current situation in these counties."
Prof. Nolan says it is unclear when clusters in meat plants will be dealt with.
"There's a lot of people being tested right now and we would expect to see quite a number of those tests come through positive.
"It could be a matter of days, it could be significantly longer.
"While these outbreaks were expected, I'm not sure we expected to see such a cluster of outbreaks in such a confined region of the country."
Some locals and business owners in the counties put under the renewed restrictions have expressed frustration at the move but Health minister Stephen Donnelly says he had to act early to stop the virus spreading to the wider community there.
"Some people are asking 'have we moved too quickly?', 'could we not have isolated the workforces involved and their close contacts and left it at that?'.
"The public health experts are absolutely clear on this: the objective is to limit the spread of the virus into the community, to vulnerable groups and so forth.
"In order to do that, you have to act before you see that spread."
Ray Walley from the GP Expert Advisory Group on Covid-19 is concerned about some complacency setting in.
"GPs nationally have been expressing for the past three or four weeks their concern that people were presenting six and seven days after symptoms.
"The difficulty is that you are six or seven days into symptoms, are you isolating?
"It might be that people are staying inside their house but they are infecting their household."