Epidemiologist Nick Wilson believes mixing Covid-19 vaccines could be a viable way to speed up New Zealand's vaccine rollout, which he felt was slowing.

Wilson's call originates from a recent article in the weekly international journal, Nature, which discussed indications mixing Covid-19 vaccines could bolster immunity to the virus.

The article referenced a 663-person study in Spain of those who had received the AstraZeneca vaccine as their first dose. About two-thirds of the study participants were then given the Pfizer vaccine as their second dose.

Researchers noted that following the second dose, participants produced much higher levels of antibodies - the proteins used by the immune system to recognise and destroy the virus.

The strategy of using two different vaccines, known as a heterologous prime and boost, had been successfully exercised against other diseases including Ebola. While the study delivered the expected result, researchers were pleased the "mix-and-match" approach pointed to a stronger immune response.

Wilson, from the University of Otago, said the study was a promising sign which deserved further consideration by those heading the New Zealand vaccine rollout - especially as concerns over the impending delivery to the general population.

Last week, Auditor-General John Ryan said a "significant scale-up" was needed if the Government was to hit its vaccination goals - and even if everything ran according to plan, the goal would only just be achieved.

Wilson said the current rollout - which had delivered 474,435 first and second doses of the Pfizer vaccine so far - did seem slow compared with other countries, referencing Israel which had fully vaccinated about half of its eight million residents within a matter of months.

Otago University epidemiologist Nick Wilson. (Photo / Supplied)

Should the availability of Pfizer vaccine add to New Zealand's rollout delays, Wilson said the results from the Spanish study were enough to warrant domestic investigation as to whether another vaccine - such as the AstraZeneca or Novavax vaccines - would have a similarly positive impact on the immunity of Kiwis who had already received the Pfizer vaccine.

"Maybe we as a country should revisit the idea of just having one vaccine which might accelerate the vaccine rollout," he said.

The Nature article did reference a British study which found people who received both the AstraZeneca and Pfizer vaccines experienced higher rates of common vaccine reactions, such as a fever. None were severe.

Wilson said such reactions were common and were not concerning.

He felt the biggest obstacle to approving a mix-and-match approach would be people's concern about taking different vaccines. However, Wilson said those fears might be allayed if it meant a more efficient rollout.

"If this evidence is pretty good which it's looking like and there was good communication, those concerns may be reduced and people might be pleased that they're getting vaccinated earlier and get a better result in terms of [immunity]."

Wilson said such a move would require flexibility within the vaccine rollout, something he believed the Government had a poor track record of given its persistence in using hotels as quarantine facilities.

As reported by the NZ Herald previously, Wilson is a strong advocate for using areas such as military bases as quarantine sites.

As at May 16, there were 353,130 vaccines available for distribution. A Ministry of Health spokesperson said that figure did not include doses in transit to DHBs.

When asked about the next three incoming shipments of Pfizer vaccine, the spokesperson refused to confirm the size and date of the orders but said each batch varied between 50,000 to 80,000 doses.

Regarding mixing vaccines, the spokesperson said health authorities around the world had generally recommended against mixing vaccine types, unless absolutely necessary, due to safety concerns such as the rare blood clotting issues associated with the AstraZeneca vaccine.

"Preliminary data is emerging from the UK and Spain on the effect of using doses of Pfizer and AstraZeneca vaccines. However, more robust data is required to understand whether there is a benefit to mixing vaccine schedules as part of New Zealand's wider rollout."