The World Health Organisation (WHO) says making sure everybody gets their second vaccine is crucial to combatting spread of the Delta variant.
The European Centre for Disease Control (ECDC) predicts the COVID-19 variant, first identified in India, will represent 90% of all cases in the European Union.
There are also concerns it could slowdown Ireland's July re-opening.
WHO spokesperson Dr Margaret Harris told Newstalk Breakfast countries need to be sensible when lifting restrictions.
"The word 'caution' is the watchword for the moment - the Delta variant is a very effective hitchhiker.
"It's better than the others at jumping from person-to-person.
"So we are seeing that it's got a huge advantage with transmission, and is becoming dominant.
"But the critical thing is can we stop it from causing severe disease and infection?
"And we certainly can [in] two ways: by taking the measures to make it impossible to jump from person-to-person, because we're not in close physical contact.
"And the second way, of course, also increase our vaccination and make sure everybody gets their second jab as well."
Dr Harris says hospitalisation figures are important.
"The real concern is again if it could evade vaccines, or if other variants could develop.
"We don't want large amount of this virus circulating in any populations around the world - because we have seen that it's got the ability to change to a more effective variant.
"So we really, really want to bring the transmission down.
"Number one thing is to reduce the admissions to hospital - because the first thing we want to do is save lives.
"And also protect the health system from being overwhelmed, so that the only thing you're dealing with is COVID - so that all the other things people need care for are not happening".
On antigen testing, Dr Harris says we need to increase our capabilities.
"Certainly upping and strengthening your testing is another crucial thing that must be done", she adds.
