The Government today announced its first Covid-19 vaccine purchase agreement. What does that mean? Science reporter Jamie Morton explains.

What's been announced?

A deal that would get New Zealand about 1.5 million Covid-19 vaccines - or enough for 750,000 people.

But that's subject to the makers of those vaccines - Pfizer and BioNTech - successfully completing Phase III clinical trials, and passing regulatory approvals here.

All going well, vaccines could be delivered to New Zealand as early as the first quarter of next year, Research, Science and Innovation Minister Megan Woods said.

"Pfizer have said they are making good progress with the development of a Covid-19 vaccine," she said.

"Subject to clinical and regulatory success, and provided the vaccine is approved for use here in New Zealand by Medsafe, it is possible that some doses will be available to us in the first part of 2021."

What's the vaccine?

Global drug giant Pfizer and German biotechnology company BioNTech are behind a group of candidates - namely one called BNT162b2 - that are among the frontrunners in the worldwide vaccine race.

Studies have so far indicated it

prompts an antibody and T cell response against SARS-CoV-2, the virus that causes Covid-19.

T-cells are white blood cells that can attack cells infected with the SARS-CoV-2 virus, while antibodies are able to neutralise the virus so that it can't infect cells when initially contracted.

Put together, you have a formidable shield against coronavirus.

As an RNA vaccine, it worked by carrying genetic material into a cell, before it coded for specific proteins from a virus.

As at this week, the vaccine was in the third and final Phase III trial at more than 120 sites around the world, with 28,000 people already having been given a second dose.

This month, the two companies launched a rolling submission to the European Medicines Agency, while Health Canada has begun a real-time review of its candidate.

Would this be the only vaccine we may use?

University of Auckland vaccinologist Associate Professor Helen Petousis-Harris said today's announcement marked the first purchase agreement - and not the last.

"There are others on the table as well," she said.

Australia, for instance, has already signed a deal to mass-manufacture Oxford University and AstraZeneca's viral vector vaccine, ChAdOx1-S, also at Phase III trial.

That's been shown to provoke a T cell response within 14 days of vaccination - and an antibody response within 28 days.

Like the influenza shots we're more used to, it's a viral vector vaccine, and uses pieces of a pathogen to effectively stimulate an immune response against it.

Petousis-Harris said another front-runner was the LNP-encapsulated mRNA vaccine developed by US' National Institute of Allergy and Infectious Diseases and Massachusetts-based Moderna.

As at this month, eight groups had 17 vaccines at Phase III.

It was widely expected the first vaccines would start rolling out either late in the second quarter, or early in the third quarter, of 2021.

"So we'd be expecting it'll be the middle of next year where we really start seeing vaccines become available," she said.

"But [the Pfizer-BioNTech candidate] could potentially arrive a little earlier than that."

How does this fit in with New Zealand's strategy?

The Government says it's complementary with other parts of our wider, recently-launched vaccine strategy, such as the global Covax Facility that could provide up to 50 per cent of our population's needs.

It's earmarked hundreds of millions of dollars - it won't disclose precisely how much, for commercial reasons - to get Kiwis and our Pacific neighbours as far up the line as possible.

"A key aim of our portfolio approach is to ensure we have flexibility and choice when it comes to securing the right vaccines for New Zealand and our Pacific neighbours," Woods said.

A task force running the strategy was now negotiating with other pharmaceutical companies, with further announcements expected next month.

Woods said "good progress" was being made on those deals, and having extra agreements in place would ensure there were enough vaccines for the whole country.

There's been concern at high levels over New Zealand getting early access.

One newly-released Cabinet paper from August indicated the Government was worried New Zealand's Covid-free status and good health could mean it wouldn't be prioritised if global prioritisation and allocation was simply left to assessment of need.

It recommended that New Zealand needed to commit "significant resource early on to help secure access to a vaccine".

Having a range of advance purchase agreements would mean potential access to a range of vaccine candidates, but that would not guarantee access to a vaccine, as "it is likely that the majority of the candidates considered will not be viable".

Those pre-payments would not be recoverable once paid.

Determining the cost of those advance agreements would be difficult, money should be allocated in order to begin, the document said.

It expected early delivery vaccines could cost between $75 and $150 per dose when later delivery could cost less than $15.

So who might get the vaccine first?

That call is yet to be made, but the Ministry of Health is working on what the immunisation programme roll-out might look like.

"A number of factors will influence who will receive what vaccines and when, such as trial data on the suitability of each vaccine for certain age groups," Health Minister Chris Hipkins said.

"We have set aside $66.3m for medical supplies and infrastructure to ensure New Zealand is ready to launch a Covid-19 Immunisation Programme as soon as we have a safe and effective vaccine.

"Most of this investment will pay for sufficient supplies to support New Zealand and Pacific Realm countries; supplies such as PPE, needles, syringes and swabs, and freezers to store a vaccine."

What about local vaccine production?