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French biotech company Valneva is nearing the end of its trial of VLA2001 - a vaccine consisting of inactivated whole virus particles, different to Pfizer's mRNA vaccine which contains the virus' spike protein.
The trial, which began in the United Kingdom, shifted to Aotearoa in search of Kiwis aged 56 and over who hadn't caught the virus and hadn't received a vaccine - a small selection pool in the UK.
New Zealand trial co-ordinating investigator Dr Simon Carson said initial theories indicated VLA2001 could provide better immunity against new variants, including Delta.
"It is thought at this stage that it may have better efficacy against Delta because it's an inactivated whole virus vaccine."
He claimed other vaccines had been developed using information about the virus' initial strain, which could make them less suited to repelling evolving variants.
However, he stressed the vaccine's effectiveness against Delta was not yet confirmed.
About 4000 people had already participated in the trial before it was moved to New Zealand, thanks in part to the country's relatively low number of Covid-19 cases and position of its vaccine rollout.
Initially required to find 150 subjects, Carson - director of Southern Clinical Trials Christchurch - was asked to double the number of participants.
Speaking to The New Zealand Herald on Monday, Carson expected to have filled all 300 spots by the end of next week.
The trial will be held across Rotorua, Waikato, Papamoa, Christchurch, Auckland and Nelson.
All trial subjects, who were medically screened beforehand, would be given one shot of the vaccine on Day 0 before a second jab on Day 28 - four weeks later.
The important point was at Day 42 when a blood test would be conducted and the data would be included in a proposal to the European Medicines Agency for the vaccine's approval.
The UK government had already purchased 100 million doses and it was expected the vaccine could be administered there later this year.
Carson noted many of the trial participants were those who held reservations about mRNA vaccines and preferred what was considered a more traditional vaccine.
However, he wanted to reassure people both types of vaccine were safe.
University of Auckland vaccinologist Dr Helen Petousis-Harris said it was early days but the vaccine did have potential.
"They have used an additional immune enhancer and that looks like it might give the vaccine additional protection, but of course that remains to be seen."
However, she said people should still have confidence in the Pfizer vaccine, in which only a small decrease in efficacy against Delta had been observed.
Medsafe group manager Chris James said the Pfizer vaccine had been "thoroughly assessed" in its safety, efficacy and quality before use.
James did not reference any plans to purchase or use the VLA2001 vaccine in New Zealand when asked to provide any detail about the vaccine or its trial.