COVID-19 Response Minister Chris Hipkins says it is "likely" that "people will need a booster" shot to keep their vaccination passes.
Vaccine certificates were introduced in November to allow those with two doses of the COVID-19 jab access to places that require proof of immunisation under the COVID Protection Framework or 'traffic light' system.
Under the new COVID-19 rules framework, which replaced the old alert level system, proof of vaccination is required when entering hospitality venues, events and other close contact businesses such as hairdressers.
At the more restrictive 'orange' and 'red' levels, for example, hospitality venues that choose not to check vaccine passes must remain contactless, while those that do check for certificates are free to open and serve guests.
The passes are valid for six months and the current requirement is two doses of the vaccine. But with the threat of the Omicron variant, the Government has been dropping hints of a booster requirement.
"Currently our vaccination passes do not have the booster set within them. It is an option we've kept open," Ardern told reporters last month.
Hipkins, after announcing on Wednesday that the interval between the second dose of vaccine and a booster had been reduced from four months to three, said it was "likely" that a booster requirement would come.
"In setting up the vaccine passport arrangements, we deliberately put an expiry date into all the vaccine passports that were issued for people who have had their first two doses, so that we could then make decisions about whether or not to simply roll that over or to introduce a booster dose requirement," he told reporters.
"We've not made a formal decision about introducing a booster dose requirement in order to keep your vaccine certificate or getting a new one, but I have previously signalled that I think it is likely that later on in the year, in order to keep your vaccine certificate, people will need a booster."
Boosters are already mandatory for border, health, education, Corrections, police, Defence Force, and Fire and Emergency staff.
With the booster interval reduced to three months, a million more people in New Zealand over 18 will be eligible from Friday.
While research shows Omicron is less severe than Delta because it is less efficiant at infiltrate the lungs, the World Health Organisation (WHO) says it should not be categorised as "mild".
The impact of Omicron is evident in Australia. New South Wales reported 11,807 new cases of COVID-19 on Wednesday and 27 deaths, while neighbouring Victoria registered 14,553 cases and 25 deaths.
Director-General of Health Dr Ashley Bloomfield said the COVID-19 Vaccine Technical Advisory Group will next week provide him with advice on whether boosters should be given to people aged 12-17.
"The science shows that people who are fully vaccinated with two doses of the Pfizer vaccine are well protected if they're infected with the Omicron variant, especially from becoming seriously ill," Dr Bloomfield told reporters.
"We've seen the impact of this most recently in our Delta outbreak. However, the protection does wane over time and it appears from emerging science, relatively quickly for protection against the Omicron variant, hence the need for boosters.
"The good news is that there's clear evidence that with that booster dose of the Pfizer vaccine, people's protection goes back up to a similar level to what it was for Delta with the two doses, and that is well over 90 percent protection against serious illness or hospitalisation.
"The evidence also suggests there is some protection from the booster against getting infected by, or transmitting, COVID-19 to others, and we continue to watch the evidence.
"With Omicron rapidly becoming the dominant form of the virus internationally, and now here in Aotearoa, it's important that we do everything we can. Moving to this three-month interval is an important measure in our efforts against Omicron and I want to urge everyone to make a plan to get your booster as soon as it is due."
With over a million doses of the Pfizer vaccine administered as a booster in New Zealand, Dr Bloomfield said: "We've not seen an increase in those common side effects, pain at the injection site, nausea, headaches and so on. For most people who do get these, they're mild and don't last long."
Ardern urged people to get a booster.
"I want to begin with an extraordinary number: 94 percent of New Zealanders aged over 12 are fully vaccinated," she told reporters.
"A year ago, achieving that level of community immunity would have seemed incredibly ambitious, but the overwhelming majority of the team of 5 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.
"Those high rates of vaccination helped stop a Delta outbreak and have given us a head-start on Omicron before it's had the opportunity to become widespread.
"But the science now tells us that to reduce the risk of Omicron, we need to get the number of people boosted as high as possible and before the outbreak really takes off.
"What we have seen overseas is that if we experience very high numbers, this will mean high numbers of our people will need hospital care. It would put our hospital system under considerable pressure and seriously disrupt other important healthcare."
Canterbury police on Wednesday extended the amnesty period to hand in fake vaccine passes until Tuesday, February 15. During an amnesty between January 26 to February 1, Rangiora police had seven allegedly forged passes handed into the station.
