The Chief Medical Officer has criticised ads encouraging people to book summer holidays - describing them as not very responsible.
Ryanair has been running a campaign with the tagline "jab and go" as part of efforts to sell seats.
The European Union says non-essential domestic and international travel should be "stongly discouraged".
It is proposing a more co-ordinated approach to travel restrictions across the bloc due to the emergence of Covid-19 variants.
A further 51 deaths linked to the virus were confirmed last night with 2,608 new cases.
NPHET has estimated the reproduction number at between 0.5 and 0.8 - and that "substantial progress" has been made in the last few weeks.