Grant Robertson says the Government is urgently working to recognise COVID-19 vaccines other than Pfizer.
But the Deputy Prime Minister doesn't know how many recently-returned Kiwis may have received a jab overseas - meaning they're not recognised as vaccinated.
"I obviously don't have that number with me… what I do know is there are about 22 vaccines that the WHO [World Health Organization] has recognised and the process that our experts are going through here in New Zealand is… 'Is that vaccine OK, or does it need a Pfizer booster on top of it for us to be confident?
"That work should be completed within the next couple of weeks and so then we'll be able to get that information back out to people," Robertson told The AM Show.
Last week, Newshub revealed Air New Zealand was lobbying the Government to recognise vaccines other than Pfizer - currently NZ's sole COVID-19 jab provider. The national carrier said about 3 percent of its pilots didn't want Pfizer and opted to get the Janssen vaccine while on a layover in the US.
That vaccine has been provisionally approved by New Zealand medicines regulator Medsafe but hasn't yet been rolled out.
Nearly 50,000 people moved to New Zealand in the 12 months up until August - many with a dose of something other than Pfizer.
"We've had a lot of people come through MIQ but, relative to the whole population, it's clearly a quite small number," Robertson said.
"That information is being worked through right now to assess those 22 vaccines and make sure that we can be confident in New Zealand about their efficacy just as we are about Pfizer."
Experts have said New Zealand's vaccination rates would rise if there were other jab choices like Janssen or AstraZeneca. Another aspect adding to COVID-19 vaccine data discrepancies is how different agencies view what New Zealand's exact population is.
Analysis by Newsroom has revealed Statistics New estimates the country's population is 5,122,600, while the Ministry of Health estimates it at just over 5 million.
"Vaccination rates are very critical to what we can expect as we release constraints on the population," said Brian Cox, an associate professor from the department of preventative and social health at Otago University.
"It only takes a small change in those vaccination rates to make quite a big difference in the control of the epidemic," Cox told Newsroom.
According to the latest Ministry of Health data, 71 percent of eligible New Zealanders are fully vaccinated against COVID-19.