A major effort is being planned to get as many people as possible fully vaccinated this month, to provide better protection against the powerful variant which originated in India.
The evidence available is that a single dose of vaccine does not provide enough safeguards against the variant.
Government sources this weekend said the Delta variant threat was not placing the further reopening at risk “at this stage” but that could change if the virus “takes off”.
A Cabinet source said: “We are in a race against time to get as many people fully vaccinated here before Delta takes off.”
From July 5, indoor hospitality for pubs and restaurants is scheduled to reopen. From that date 200 people will be allowed attend sporting events, or up to 500 at venues that can accommodate 5,000 or more. Non-essential international travel is set to resume from July 19.
Also in July the numbers permitted at outdoor organised events are to increase to a maximum of 500, while the number of people allowed to attend weddings is to increase to 50.
If the Delta variant takes off in the next few weeks it has the potential to set back plans already made by businesses, the hospital sector, and the wider public.
With more than three million adults now vaccinated with at least one dose, the HSE has begun examining how to roll-out the jab to 12 to 15-year-olds.
The HSE’s National Immunisation Office has conducted preliminary “horizon scanning” on how the vaccine will be administered to adolescents, a HSE spokesman confirmed. However, a decision has yet to be made on whether it should be offered to children later in the summer or when they return to school.
Meanwhile the National Immunisation Advisory Body (Niac) is expected to approve a vaccine for 12 to 15-year-olds as soon as this week, say sources.
Government sources yesterday admitted they “are a bit worried” about the Delta variant. Concerns were heightened at a meeting of the British-Irish Council last week, which was attended by Taoiseach Micheál Martin and Tánaiste Leo Varadkar, as well as officials.
The Irish contingent were briefed on developments across the UK, where the Delta variant is spreading rapidly, with a doubling of outbreaks in schools and educational settings over the last two weeks in May.
Latest figures show there are only 126 cases of the variant here, which is only slightly up on the previous week.
However, in Ireland less than 30pc of cases are genetically sequenced, so the actual number of variant cases is likely to be higher.
The cyber attack on the HSE also means there is a delay in reporting results.
In Northern Ireland, however, cases of the Delta variant have risen rapidly to over 20pc of all cases, and in England cases are doubling every 4.5 days in some parts, with the variant now accounting for 75pc of infections. It is also dominant in Scotland.
According to a Government source: “It is very likely it will become the dominant strain here too, and across Europe.”
At the British-Irish Council meeting, UK officials told how hospitalisations were now rising rapidly, particularly among those who have received no vaccine at all but, also, crucially among people who have had only a single dose.
“So, we need to get as many people vaccinated as we can before going ahead with the next phase of reopening in July — the double jab works against the Delta variant,” the Government source said.
It is thought narrowing the gap between the first and second dose to the AstraZeneca vaccine to eight weeks will be useful in the looming battle ahead.
The Government is also expecting large batches of the Pfizer vaccine this week and next, to provide seconds jabs to those who have already received a first dose.
As of now, Covid numbers are still trending in the right direction in Ireland, with the number of detected cases, hospital and ICU admissions down.
A Government source added: “We just need to step things up and not be complacent in any way, in relation to vaccination, test and trace, asking the public to stay vigilant and to avoid indoor gatherings.
However, sources admit: “The Delta variant is a black cloud on the horizon and it’s not getting any smaller.”