During the Brexit transition period, the EC regulations continue to apply as before, and these take priority over social security reciprocal agreements the UK has with various countries, and over the UK’s domestic NIC legislation. These regulations apply in respect of EEA states which, at the time of writing, are:
Ireland (The Republic)
Switzerland (note 1)
UK (note 2)
(1)Switzerland is not an EEA country but applies EC social security regulations.