An advisor to the World Health Organisation says the Irish government should not build its Covid-19 strategy around a possible vaccine.
Dr Johann Giesecke, from Sweden, will tell the Dáil's coronavirus committee this morning there may be a long wait for one.
He will also say the vaccine may not be effective on those who need it the most.
Dr Giesecke will also advise the government to allow the virus to spread in a "controlled" way among people under the age of 60.
He says they should concentrate on the old and frail, with frequent tests of staff and residents in care homes.
But infectious diseases professor Sam McConkey, who will also appear before the committee, says that is not the right approach to take.
"I completely disagree with that," he told Newstalk.
"He's a Swedish epidemiologist, and Sweden has taken a bit of a different line.
"There are a number of issues there; number one, Sweden has a significantly higher death rate than ours so it has not work.
"Number two, their economy has dropped more than that of Finland and Norway and comparable Nordic economies, so the idea that somehow doing that would protect the economy is false and flawed and not backed up by the data."
Professor McConkey has also warned that Dublin could need to go to Level 4 or even Level 5 as cases continue to rise.
He said this is the time to take action.
“The earlier we do it, the less duration and the less restrictive those measures will have to be,” he told Newstalk.
"The rate of Covid-19 cases has gone up in four or five counties to almost the same level as Dublin and action is required now," he added.
“Unfortunately, if the number of cases continues to rise, whether in Dublin or in those counties, then, unfortunately, the only sensible thing to do is to go up to Level Four or even Level Five.”
A further 334 new cases of Covid-19 were confirmed by the Department of Health, bringing the total number of cases to 33,444 in Ireland, with 174 of them in Dublin and 34 in Cork.
More than 70% of the cases were people under the age of 45.
The Department of Health’s acting chief medical officer said the virus was spreading disproportionately among teenagers and those in their twenties and early thirties.
Dr Ronan Glynn said people aged 15-34 accounts for 40% of Covid-19 cases in the past two months, despite accounting for a quarter of the population.
“For teenagers and people in their 20s and 30s in particular, I know that what has been, and is being asked of you again, is extraordinary,” he said.
“This pandemic has impacted on your education, your employment, your relationships and your social lives. The vast majority have done the right thing – have heeded public health advice and kept themselves and their families safe.
“But the disease is continuing to spread disproportionately among younger people at present. And so, I am asking you to stick with this and continue to follow the public health advice."