A new Omicron variant is about 10 to 20% more transmissible, according to sequencing data from the UK, where more than 1,000 cases have been identified.
The new form of the virus, known as Omicron XE, is a recombinant of the Omicron BA.1 and BA.2 variants.
A small number of cases of the new Omicron strain have been discovered in Northern Ireland.
The Department of Health has said that as of 8 April, one case of the XE variant has been reported in the Republic of Ireland to date, in a travel-associated case with a specimen date in February 2022.
It said no further cases of XE have been reported in Ireland since then.
Speaking on RTÉ's Morning Ireland, Professor of Immunology at Trinity College Kingston Mills there was a series of new variants emerging in India, with six million cases in April alone.
"It has not been as good at vaccinations as other countries, we have to watch that carefully and not get complacent about the fact that the pandemic is complete.
"I am not trying to be scaremongering but we need to be prepared if we do see a variant that completely evades immunity with the vaccines."
Prof Mills added that current vaccines will "probably" be effective against Omicron XE.
His comments come as the number of people with Covid-19 in hospital has reduced further.
As of this morning, there were 742 people in hospital with the virus, down 12 since yesterday.
This is a 45% reduction compared to the 1,360 patients with tested positive for the virus two weeks ago.
There were 48 people in ICUs with Covid-19, an increase of three since yesterday.
Overall, the number of patients being treated for the virus in intensive care units is down 10% compared to two weeks ago, when 54 people were in ICUs.