The green light is expected in the coming days to offer both the Johnson & Johnson and AstraZeneca Covid-19 jabs to people aged 40-49 paving the way for vaccination of this group to start this month.

The HSE is expected to announce people in their 40s can begin registering for a vaccine shortly.

Vaccination could start at the end of this month and extend into June.

It is understood the recommendation from the National Immunisation Advisory Committee (Niac) is to allow both vaccines be offered to people from the age of 40 – changing the current restriction confining them to those over 50.

It was originally believed the recommendation would be confined to the Johnson & Johnson vaccine with the cut off at age 45.

Both vaccines can now be used in people over 40 but anyone who is offered one in this age group will be asked for their consent after the very small risk of unusual blood clots is explained.

The vaccines will also be used in those over 40 where alternatives are not available.

The recommendation is believed to have been supported by the chief medical officer Dr Tony Holohan and it is now a matter for the HSE to implement it.

The decision is seen as a boost to the roll-out of the vaccine and comes as the HSE has managed to continue with the administration of the vaccines since last week’s cyber attack.

Everyone with an appointment who turns up at the designated vaccination centre or GP surgery will continue to be given a vaccine this week.

The portal to apply for a vaccine is currently open to people in their 50s and 60s.

Asked when people in their 40s can register for a vaccine, HSE chief clinical officer Dr Colm Henry said yesterday: “We will be announcing that later on in the week.

“At this point in time we invited people from May 4 onwards to register who are 50 to 59,” he told RTE radio.

He said the experience so far is that around 80-85pc of people who apply for a vaccine register on the portal rather than over the phone.

Commenting on when the over-40s would be told he said: “We will be publicly communicating that very clearly as we did with the 60 to 69 year olds and the 50 to 59.

“We expect that to progress in larger numbers in that decade than before. We expect that to go right through the month later in May and the month of June.”

He said the HSE received the outcome of the Niac recommendation at the end of the week.

“Clearly what we want to do is progress with a safe, effective vaccination programme at speed and at pace to cover as much of the population as possible. And using the stocks of vaccines that are coming into the country in the most effective and safe way.

“We need time. We have just received the information ourselves.

He declined to say what the Niac recommendation was at this point.

“The HSE will be going through that in the coming days, and I expect we will come to an operation decision ourselves in mid week.”

The target is to have around 82pc of the adult population with at least one dose by the end of next month.

Over two million doses of Covid-19 vaccines have been administered with over 500,000 fully protected.

In the UK more than eight in 10 people aged 40 and above in England have now had at least one dose of a Covid vaccine.

The HSE indicated last week that it may be able to give a timetable this week indicating when people of all age groups are likely to be offered a vaccine.

It is unclear if the cyber attack will delay this kind of modelling to be done.

Much depends on expected deliveries of the vaccine materialising.

Vaccination has already been credited with dramatically reducing levels of serious illness, hospitalisations and death among older age groups.