Most of the population has built up no immunity to the coronavirus, leaving them at risk of infection as the country begins to ease the lockdown.
Prof Paul Moynagh, head of the Department of Biology in Maynooth University, said although official figures show a total of 23,135 cases of the virus here so far it is likely the real number who have been infected is around 300,000.
He said people who have had the virus and recovered can develop antibodies which could potentially shield them from reinfection, although some scientists question the protection.
"There is a lot of commentary on this," he said.
"We probably have immunity and are more uncertain how long that immunity lasts for."
Based on a possible estimated case fatality of around 0.5pc, it would mean that around 300,000 people here could have picked up the infection and recovered.
It would mean around 6pc of the population had suffered the infection but in order for herd immunity to apply that would need to be 60-80pc, Prof Moynagh said.
Herd immunity is the indirect protection from a contagious infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection.
Other countries have taken blood samples randomly in the population to determine how many had antibodies and could have built up potential immunity, he said.
"We won't know for sure how many could have developed antibodies after getting the virus until we do a test in this country," he added.
The National Public Health Emergency Team has indicated it plans to do likewise in this country but it has yet to find a test which is reliable.
The samples would help show how many had the infection and what the level of immunity is among the general public. "The immunity is unlikely to be lifelong but it could potentially last one to two years," he said.
Prof Moynagh added that there needs to be continued emphasis on physical distancing as well as other measures along with "smart testing" when the lockdown is eased.
"My point in relation to smart testing is that you can be very busy doing tests but if it is not done with speed then two days are lost," he said.
Kingston Mills, professor of experimental immunology, in Trinity College, said that the true level of infection could range from 200,000 to 600,000 people.
Many people may have got the infection and been asymptomatic, while others who had one symptom and did not fall into a priority group were not eligible for a test until recently, he pointed out.
He believes people who have had the virus and develop an antibody response are likely to have developed immunity to infection, which is longer than the three months recently suggested by the National Public Health Emergency Team.
Commenting on the loosening of lockdown measures, he said he did not foresee high risks in opening up DIY shops or outdoor cafés or restaurants as long as physical distancing and the hygiene etiquette were maintained.
"There could be big problems where you have large numbers of people working in confined spaces such as shared offices," he said.
"There is a strong case for people to continue to work from home if they can continue to do so."
If someone has had the virus and developed the antibodies it does not give them a licence to behave as normal and they must continue to observe distancing, he added.