The Health Minister is making an urgent law change after a High Court has ruled it was "reasonably arguable" the Government's provisional approval of the Pfizer Covid-19 vaccine is "problematic".

The case - Nga Kaitiaki Tuku Ihu Medical Action Society Incorporated v The Minister of Health - was in the High Court at Wellington last week.

In a decision released today, Judge Rebecca Ellis said: "it is reasonably arguable that the decision to provisionally approve the vaccine for much wider use is problematic" and went beyond the powers of section 23 of the Medicines Act.

Doing so could undermine public confidence in the vaccine and waste vaccine stock that already in New Zealand.

What Ellis said could be problematic was the vaccine being granted for a limited number of New Zealanders - namely those aged over 16.

"While I acknowledge that this is a more "limited" class of persons than "all New Zealanders", a class of that size seems well beyond what is contemplated by a straightforward, purposive, reading of the section," she said.

However, Ellis declined to grant interim orders stopping the vaccine rollout - sought by the plaintiff - on the basis the repercussions "are too great, by some very considerable margin".

In response, Health Minister Andrew Little said the Government was making an urgent "technical amendment to modernise the law".

Little said section 23 had been used over 40 years by successive governments to grant early access to approved medicines when there was public good.

"The law has for some time now, lacked clarity over how it can be applied," Little said.

"We already knew the Medicines Act was out of date, which is why we were planning to replace it with a new Therapeutic Products Act.

"Treatments approved under Section 23 go through a rigorous Medsafe approvals process. There are occasions when the health needs of a population call for urgent access to a medicine, vaccine or treatment and we need to keep this option available for some circumstances."

There were six products currently in use under Section 23, including two types of contraceptives, two pandemic flu vaccines, the Pfizer Covid-19 vaccine and an electrolyte solution used in hospitals, potentially affected by the decision.

"The Government will introduce a Bill tomorrow to make sure New Zealanders continue to have timely access to the medicines and treatments they need. The Medicines Amendment Bill is expected to be passed under urgency tomorrow in order to protect New Zealanders early access to medicines when needed," Little said.

Legal challenge

Much of the case by applicant Nga Kaitiaki Tuku Ihu Inc had focused on whether the vaccine being rolled out to the majority of the country fitted within the provisional consent legislation in the Medicines Act that it had been granted under.

The vaccine, Pfizer-BioNTech Covid 19, has been formally tested on more than 40,000 people - half received the vaccine, the other half a placebo which consisted of slightly salty water. Since it started being used widely, tens of millions of people have now received it.

In a press release, the group said the judge had agreed that everyone in New Zealand over 16 is not a limited number of patients.