Second jabs for the over-50s and clinically vulnerable will be given eight weeks after the first, the PM says.
The government in Lisbon says anyone arriving will need to take a negative PCR test before departure.
First Minister Nicola Sturgeon made the announcement as cases continued to increase in Glasgow.
The NI agriculture minister will succeed Arlene Foster as leader of the Democratic Unionist Party.
The corporation said he was leaving his post due to ongoing health issues.