The gap between second and third doses of the Covid-19 vaccine is being shortened from four months to three, the government has announced.

Prime Minister Jacinda Ardern, Covid-19 Response Minister Chris Hipkins and Director-General of Health Ashley Bloomfield made the announcement this afternoon.

Ardern said Cabinet made the decision on the advice of the Vaccine Technical Advisory Group, and it would mean a million more New Zealanders would be eligible for their booster shot.

The shorter interval, which only applies to the Pfizer vaccine, would take effect on Friday, 4 February.

"It now means a total of 3,063,823 people aged 18 and over - two thirds of our population - will be eligible for their booster from this weekend. Over 1.3 million people have already got theirs," Hipkins said.

The change would mean more people, especially Māori, would be able to receive a booster before Omicron took hold, he said, urging anyone who was eligible to get their booster as soon as possible.

Ardern said an extra 100,000 Māori will be eligible for a booster, representing a 59 percent increase in Māori eligibility from Friday, while an additional 52,000 Pacific people will be eligible, representing a 47 percent increase.

Ardern said the reason for getting the booster was clear - Omicron was usually more mild, but it could be severe for some.

"So don't think getting a booster is just about keeping yourself safe, it's about ensuring our hospital and health system is not overwhelmed so those you love and everyone in our community who needs our hospitals can get the care they need."

Hipkins said New Zealand was one of the top-10 most vaccinated countries in the OECD, and the earlier booster would also help reduce the impacts of Omicron on workforces and supply chains.

"We have given ourselves a head start that we cannot afford to give up," he said.

People can check their eligibility on MyCovidRecord, by referring to their vaccine appointment card, or calling 0800 28 29 26 between 8am and 8pm seven days a week.

Ardern said today that 94 percent of New Zealanders over the age of 12 were fully vaccinated.

"A year ago, achieving that level of community immunity would have been considered incredibly ambitious, but the overwhelming majority of the team of five million have done what they've done best this entire pandemic, banded together and turned out to get vaccinated not just for themselves but to keep their loved ones and communities safe."

The high rates had helped stop a Delta outbreak and given New Zealand a head start against Omicron, but now the number boosted needed to get as high as possible, she said.

The government would create a big booster campaign during February, with details to be provided by the Ministry of Health next week, Ardern said.

Director-General of Health Dr Ashley Bloomfield speaking about boosters this afternoon. Photo: RNZ

Dr Bloomfield acknowledged the work put in by vaccination teams across the country in achieving 94 percent vaccination. Māori vaccination rates were now up to 90 percent first dose and 85 percent second dose, he said.

Ardern said there had been a significant boost in funding for community organisations which was helping support the efforts to help vaccinate Māori around the country.

"What we've had to do is make sure that we've stood up a system that worked for Delta, now we need to make sure that we are able to expand to deal with what will be a larger number of cases but actually the majority of cases won't need the level of care that delta may have required. So that has been an ongoing programme of work with our Māori providers."

Dr Bloomfield said the impact of waning protection over time from the vaccine had been seen.

"The good news is that there is clear evidence with that booster dose of the Pfizer vaccine, that people's protection goes back up to a similar level to what it was for Delta with two doses, and that is well over 90 percent protection against hospitalisation or serious illness."

He urged everyone to make a plan, and said there was excellent capacity for vaccinations across the system.

"Whilst we can't administer boosters to everyone in that one million this Friday, I can assure you we have excellent capacity across our system and we certainly have a good supply of vaccine."

It was even more important for vulnerable people and those working in higher-risk settings to get the booster, and considerable work was under way to make boosters as available as possible to those people, Bloomfield said.

New Zealand data so far was similar to that overseas - we had not seen an increase in side effects, and overall adverse events after each additional vaccination had declined, he said.

He had asked for advice on when 12- to 17-year-olds would be able to get booster doses.

Ardern said the reason behind the delay until Friday was the government needed to make sure all the infrastructure was stood up.

New Zealand was still relatively early on in its Omicron outbreak compared to other countries, and there was still time for people to get their booster in the coming week and have the benefit of it before the variant spread widely, she said.

Dr Bloomfield said New Zealand was an early mover in reducing the booster interval from six months to four, and was moving to reduce the interval again to three months before the Omicron outbreak, which was something many other countries did not have the opportunity to do.

Ministry of Health Chief Science Advisor Ian Town said bringing it forward to three months, which had been done in the UK and in many Australian states, meant New Zealand could get the level of antibodies at a peak before it was facing widespread transmission.

There did not appear to be any downside to reducing the interval to three months, he said.

Dr Bloomfield said he wanted to emphasise that the evidence was clear that while two doses was great for Delta, that was not the case with Omicron, "so we will be pushing really hard to vaccinate".

There were 142 community cases of Covid-19 and 54 border cases reported in New Zealand today. There were 38,332 booster doses given yesterday.

This morning, Deputy Prime Minister Grant Robertson defended the government's approach to pregnant journalist Charlotte Bellis' emergency MIQ requests, and its acquisition of rapid antigen tests (RATs) ahead of an expected rapid increase in Omicron variant cases across New Zealand.

National has been calling for borders to reopen immediately, and frequent RAT testing in schools.

Cabinet yesterday discussed its plans for reopening the borders, and Prime Minister Jacinda Ardern is expected to make announcements about that tomorrow. A staged timeline was outlined late last year, but was quickly delayed because of the risks posed by Omicron.

The government this morning announced it would adding $70.7 million to its Events Support Scheme, and extending coverage to events scheduled for before 31 January next year that were planned before being cancelled by the red traffic light setting.