Leo Varadkar (Dublin West, Fine Gael) | Oireachtas source

People coming in from the United Kingdom or South Africa — there are no direct flights from South Africa but people could come in from other airports — are required to have a negative PCR test before landing in the country. It is mandatory. They are then strongly advised to self-isolate for 14 days; that is not mandatory.

On sharing information with Northern Ireland, we have an information exchange. I understand there are some difficulties with our sharing data with Northern Ireland. We are very happy to do so, in principle, but I am told there are some difficulties with the format and the details of the requests and so on. We will resolve that. We intend to do so. The big flaw for Ireland in imposing 14-day mandatory quarantine with hotel detention for people arriving in our ports and airports is that it would be largely ineffective because we could not do so on the land border with Northern Ireland. Without stating the obvious, countries that have done this successfully are island states — we are an island geographically but not an island state — or countries such as South Korea, which has a border with North Korea that is of a very different type than ours with Northern Ireland.

See this speech in context