Professor Luke O'Neill says Ireland should not vaccinate anyone under 12 years of age.
It comes amid concerns a Lambda variant of COVID-19 discovered in Peru may be more vaccine resistant than others.
While a massive research project has shown children are less affected by the virus over the longer-term.
Over 250,000 children, aged five to 17 years, who were infected with COVID-19 were examined from February.
It found that younger children had symptoms for fewer days than their older counterparts.
While Prof O'Neill says a vaccine-resistant strain is possible but unlikely.
But he told The Pat Kenny Show: "There's a remote chance of a nasty variant emerging that'll break through everything and then we'll go back to square one.
"That's our last remaining scientific worry, in a way.
"This is why we shouldn't vaccinate the under-12s in my opinion at the moment: give the vaccine away to developing countries to stop variants.
"Our biggest concern is new variants really... to stop it, and it's running rampant in all these countries.
"So just in case a nasty variant crops up we've got to prepare, in a way, for that - and try to mitigate against it by getting widespread, global vaccination".
Meanwhile the World Health Organisation (WHO) has called on wealthy countries to suspend the use of COVID-19 vaccine 'booster' shots until at least the end of September.
WHO Director-General Dr Tedros Adhanom Ghebreyesus says the focus must now be on getting more vaccines to low-income countries.
Prof O'Neill agrees this is what should be done.
"That makes sense to me, because we don't want these variants cropping up," he says.
Earlier the head of Oxfam Ireland suggested it could take up to three years for the world's population to be vaccinated at the current rate.
Jim Clarken told Newstalk Breakfast: "Just 1.2% of the population in developing countries have been vaccinated so far, so we're a very long way from having a reasonable number.
"We see that there's a huge inequity in the way that the vaccines are being shared and distributed.
"At the start of all this, if you recall, the wealthiest countries in the world were competing with each other essentially - but also competing with poor parts of the world to shore up as much vaccine as they possibly could.
"The key point is that a very large part of the population of the world has not been vaccinated, and won't be vaccinated at the rate we're going, for another two or three years possibly."