Ireland is in the middle of another wave of Covid-19, driven largely by Omicron sub-variants, according to the HSE's Chief Clinical Officer.

Dr Colm Henry said the sub-variants now comprise about 90% of cases that they are doing genomic sequencing on.

Speaking on RTE's New at One, he said: "These new variants mean that the people who were previously infected with Delta, such as in summer, autumn of last year, or even that we call the BA.1 variant earlier this year, don't enjoy that protection from reinfection from these variants.

"And what we're seeing now, it highlights the fact that even though we're in a much better position as a country in relation to Covid compared to previous summers, it highlights how much uncertainty still remains".

He said this shows that Covid is not seasonal, but is a "virus for all seasons".

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Dr Henry said there is increasing pressure on hospitals, although generally people are not getting as sick as before.

He said the experience in Portugal, which is some weeks ahead of Ireland, demonstrates that it is a plateau of four to six weeks and then cases begin to fall.

He said presentations in emergency departments are at record highs towards the end of June, which is "something we normally associate with the middle of winter."

Dr Henry also said in relation to an emergency response plan to tackle future outbreaks of Covid, there has been a move away from a population-based mass testing and contact tracing every case, "which is no longer appropriate and no longer really possible given the kind of measures that would involve".

Instead, there is a move towards "a mitigation approach which involves protecting vulnerable individuals, vulnerable groups, and vulnerable settings.

"But of course, because of these recent mutations with the surge in cases, it highlights the unpredictability of this virus, and that means we have to be ready for any surge in cases and that testing that would be required, be that PCR testing or antigen testing."

31 people in ICU with Covid-19

It comes as there has been a slight increase in the numbers of people in hospital with Covid-19.

As of 8am, there were 776 people in hospital with the virus, an increase of 25 on the same time yesterday.

Of these, 31 people are in intensive care units with Covid-19, an increase of three since yesterday.

The Health Service Executive said more staff are testing positive in acute hospital settings - with almost 600 staff members testing positive in the last week - which is putting increased pressure on hospital services.

Meanwhile, Minister for Health Stephen Donnelly has asked NIAC to examine if a fourth vaccine should be administered to people aged under 65 years later this year.

The minister said the National Immunisation Advisory Committee has so far not signalled its views either way on this question.

He pointed out that there is not yet a common approach internationally to this issue.However, the minister said he feels it is the right time to examine the issue given that Government is now drawing up plans for autumn.

Minister for Finance Paschal Donohoe has said that legislation will be considered by the Cabinet around when a mask mandate might be needed.

He said people in Ireland have seen the effectiveness of mask wearing in tackling the rise of Covid-19.

Speaking on RTÉ's Morning Ireland, Mr Donohoe said Covid infection numbers are rising and urged people who have not yet received a booster dose to do so.

"In particular, for those who are in their late 60s, for those who are immuno-compromised our message is please avail of the booster campaign because that is the greatest line of defence to the disease and getting very sick and impacting on your health and that of those who are near you. And that's where we will focus.

"The key point here is just to emphasise the message that we learned so well over the last year.

"Vaccines work, they can really play such a vital role in minimising the impact this disease can have on your health, and we would just encourage all who have not received our booth to campaign their booster vaccination yet to please do so," he said.