NPHET is worried about the significant number of people traveling abroad who have not yet been fully vaccinated.
It says while unvaccinated travel isn't fueling another wave, it presents a real risk to individuals.
It's estimated that daily case numbers would currently be over 10 thousand if it wasn't for the vaccination programme.
Chair of NPHET's Modeling Group Professor Philip Nolan is appealing to people who are not yet fully vaccinated to cancel any planned holidays.
He says "not many but some" holidaymakers could end up severely ill.
"More worryingly, they could infect someone who they love very much, who is vaccinated but is vulnerable".
Prof Nolan says a transmission in this instance could cause significant or severe infection.