A member of the National Public Health Emergency Team (NPHET) says restrictions on indoor dining in pubs and restaurants may have to stay in place for more than three weeks.
The Level Three measures in Dublin mean only places doing takeaway or with outdoor seating can stay open.
Professor Philip Nolan says there is clear evidence that the virus spreads when people gather indoors, in places like bars, restaurants and gyms.
"One in four cases across the country, one in three cases at least in Dublin, are community transmission and it's happening in these settings where people gather.
"Unfortunately, for the next few weeks at least, we're going to have to have nobody gathering in those settings and for some weeks thereafter."
Taoiseach Micheál Martin announced the decision to move Dublin to Level Three of the new Living with Covid-19 plan on Friday, limiting the number of people who can visit a household.
The restrictions also mean that spectators are not permitted at sporting events and people within the county are being asked not to travel outside of Dublin unless it is for an essential reason.
The current restrictions are due to remain in place until at least October 9th.
Representative bodies from the tourism and hospitality industry criticised the decision to impose increased restrictions on Dublin business, saying a small number of cases in Ireland were identifying bars and restaurants as the source of transmission.
In a series of tweets earlier this week, Prof Nolan explained how the delay in the outset of symptoms has a bearing on what transmission source is attributed to cases.
