The booster vaccine programme will open to all remaining age groups earlier than expected, the Minister for Health has announced.

Stephen Donnelly said: "From this Sunday (January 2) all those aged 16 and older who are eligible to receive a booster vaccine can access this service via HSE vaccination centres.

"GPs and community pharmacies will also be providing this service, on an appointment basis."

The roll-out will now commence to all age groups eight days earlier than planned. The original date was 10 January.

Taoiseach Micheál Martin, also posting on Twitter, said people can book a vaccine centre appointment for boosters from tonight " or contact your GP or pharmacist".

He added: "Boosters are our best protection against Omicron, so please get one when you can."

Vaccination clinics will commence appointment-based clinics for those aged under 30 years in designated centres. People can book appointments from later this evening, the Department of Health said in a statement.

GPs will continue to vaccinate down through the age groups, by appointment. Pharmacies will also continue to vaccinate people by appointment.

Minister Donnelly added: "This acceleration of the programmes means that many of our vaccination centres will now be administering primary, booster and paediatric doses of Covid-19 vaccine.

"Further clinics will be scheduled over the coming days. Appointments will be booked through the HSE online system."

Children aged 5 to 11 will be offered a primary dose of Covid-19 from 8 January. The portal to book an appointment for them is already open.

The HSE said people aged 16 to 29 years will be offered a single dose of Pfizer/BioNTech vaccine. This age cohort can receive this vaccine even if they got a different vaccine for their primary course.

"Please ensure you are at least three months post second dose as this will be checked at the vaccination centre."

The HSE added: "If you had Covid-19 since you were vaccinated, you should get your booster dose at least three months after your positive test result."

Earlier, Mr Donnelly said people should follow the Chief Medical Officer's advice and reduce the number of other households they meet indoors "to the greatest extent possible".

Asked if this was now Government policy, Stephen Donnelly said that it was the public health advice.

Speaking on RTÉ's News at One, he said Government policy was last agreed on 22 December and that was for a maximum of three other households visiting another.

"This is a maximum but right now we need to minimise the other households we meet up with. Cabinet has not met since so there has not been formal updated advice," he said.

CMO Dr Tony Holohan had urged people not to hold household gatherings tonight to celebrate New Year's Eve amid concern over high levels of Covid-19 transmission.

Yesterday, for the fourth time this week, Ireland recorded its highest number of confirmed cases of Covid-19.

The Omicron variant now accounts for 92% of all cases.

Sinn Féin's health spokesperson David Cullinane has accused the Government of causing confusion over the advice around household gatherings, saying that he can "understand why there is confusion at the moment because we have the Minister for Health saying one thing and we have the CMO saying something else."

He said "it would be far better if that public health advice was aligned in relation to what the Government and NPHET were saying."

In a post on Twitter, Dr Holohan said: "The most effective way to minimise the risk of any of us transmitting this virus to others is to avoid mixing indoors with people from other households.

"I know this is not the advice any one of us wants to hear, particularly in advance of New Year celebrations.

"However, given the current profile of the disease, it is essential that all of us continue to keep our social contacts as low as possible in the days ahead."

Official advice remains that visits to private homes should be kept to a maximum of three other households, for a total of four households.

However, the Government advice also says "it is recognised there are specific days and dates (25, 26 and 31 December) in the calendar which are important social and cultural occasions where families will likely choose to come together in larger household numbers".

Speaking on RTÉ's Morning Ireland, Dr Holohan said limiting contacts is important in limiting transmission.

He said there has been a "significant surge in infection" that has "continued unabated" and public health officials think there could have been as many as 30,000 cases yesterday were it not for constraints with testing capacity.

"These are very significant numbers of infection, and I think the only responsible message from a public health point of view that the public can hear is - what can I do as an individual to keep myself and my family, particularly if I'm not boosted?"

Dr Holohan said meeting up in large numbers of four households at this point in time is simply not safe. He said it is important for people to hear that message.

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Dr Holohan said that without the vaccination programme the current high case numbers would mean "very, very significant numbers" of hospitalisations and "potentially of deaths".

He said there is a "substantial amount of protection" against severe disease for those who have been vaccinated and boosted.

"Vaccines work, the boosters work, they protect you - if you pick up this infection - from becoming a severe infection, so that's an enormous difference from last year, even though we're dealing with much, much bigger case numbers," Dr Holohan said.

"The reality now that we find ourselves in is we see a very significant surge of this new Omicron variant ... and we're seeing some early signs that are giving us concern in terms of hospitalisation the first three days of this week.

"We're seeing hospitalisations exceeding 100 per day... over the course of most of December we were averaging maybe 50/60 per day.

"So that gives us cause for concern."

Dr Holohan said it is too early to conclude that they understand what the pattern of hospitalisation is going to be as a result of this disease, but they do have good reason to believe that Omicron is "less likely to result in severe disease" and less likely to result in hospitalisation for an individual.

However, he said if something is half as likely to produce a severe outcome like hospitalisation, but there are five times more cases, there can still be a much bigger effect at a population level.

"So we have this almost paradoxical situation that something represents a lower risk to an individual, and still be a bigger problem for a population," he said.

"So we're in a situation as a country where we simply will not be able to manage within the health service and we'll have challenges across many other essential services if we have many, many more people being infected at the same time."