Kiwi scientists are buoyed at the latest breakthroughs in the global race for a Covid-19 vaccine, with hopes that crucial Phase III trial results could be out by the year's end.
This morning, researchers from Oxford University's Jenner Institute and the Oxford Vaccine Group reported an experimental vaccine, so far tested on 1077 healthy adults, triggered a protective immune response among those aged 18 to 55.
Critically, the researchers found their vaccine was "safe and tolerated".
The vaccine, labelled ChAdOx1 nCoV-19, provoked a T cell response within 14 days of vaccination, and an antibody response within 28 days.
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 cannot infect cells when initially contracted.
During the study, participants who received the vaccine had detectable neutralising antibodies, which have been suggested by researchers as important for protection, and these responses were strongest after a booster dose, with 100 per cent of participants' blood having neutralising activity against the coronavirus.
The next step in studying the vaccine was to confirm that it can effectively protect against SARS-CoV-2 infection.
But already, the researchers said the vaccine did not lead to any unexpected reactions and had a similar safety profile to previous vaccines of its type.
"We saw the strongest immune response in the 10 participants who received two doses of the vaccine, indicating that this might be a good strategy for vaccination," said Professor Andrew Pollard, head of the Oxford Vaccine Group.
Also published in medical journal The Lancet today were results from a phase II trial of Ad5 vectored Covid-19 vaccine candidate, being developed by China's CanSino Biologics.
The results, which came from a wider group of participants than a phase 1 trial carried out in May, showed the vaccine was also safe and induced an immune response.
And earlier this month, scientists at the US' National Institute of Allergy and Infectious Diseases and Massachusetts-based Moderna this month reported their investigational vaccine was generally well tolerated and prompted neutralising antibody activity in healthy adults.
The vaccine, called mRNA-1273, was designed to induce neutralising antibodies directed at a portion of the coronavirus "spike" protein, which the virus uses to bind to and enter human cells.
Three groups of 15 participants received two intramuscular injections, 28 days apart, of either 25, 100 or 250 micrograms (mcg) of the investigational vaccine.
All the participants received one injection; 42 received both scheduled injections.
No serious adverse events were reported, although more than half of the participants reported fatigue, headache, chills, myalgia or pain at the injection site.
Systemic adverse events were more common following the second vaccination and in those who received the highest vaccine dose.
An interim analysis found two doses of vaccine prompted high levels of neutralising antibody activity that were above the average values seen in convalescent sera obtained from Covid-19 patients, and a phase 3 efficacy trial was set to begin this month.
University of Auckland vaccinologist Associate Professor Helen Petousis-Harris was encouraged by the results so far.
"In order to be effective, vaccines need to elicit the right type of immune response against the right targets," she said.
"In the case of Covid-19, most vaccines are targeting what is called the spike protein, which the virus uses to gain entry into our cells and infect them."
While the Oxford and CanSino vaccines were both viral vector vaccines, the viruses used to carry the SARS-Covid-19 spike protein gene were different, she said.
"While the Oxford vaccine uses a virus that does not normally infect humans, the Chinese version uses a virus that does commonly infect humans.
"There is a possibility that vaccines made with the human virus may be less effective because some people may already be immune to them."
Petousis-Harris said there were recent reports suggesting protection from a Covid-19 vaccine may be brief, but these were largely based on recovered cases where antibodies were observed to wane.
"This does not mean that these people are not still protected and it does not mean that vaccine protection might be short-lived," she said.
"There are a number of mechanisms involved in protection that we are not measuring and, with respect to Covid-19, do not yet fully understand.
"Ultimately we will only know the effectiveness of these vaccines once they have been through the next phases of study and the rates of Covid-19 in people who received the vaccine can be compared with the rates in people who received a placebo.
"The length of time people are protected for will not be known for much longer. So far, these vaccines appear to be pushing the right buttons and we can be cautiously optimistic."
Otago University immunologist Associate Professor James Ussher also said the early data looked promising.
"The next question will be whether these immune responses are going to be able to protect against infection and disease in people," he said.
"The pre-clinical data looks like these vaccines can protect against disease in animal models, but don't necessarily completely protect against infection, so we'll need to wait for phase 3 results to really see whether they work in humans, and that they're safe in larger groups."
Ussher said the speed at which teams around the world were pushing for a vaccine was "unprecedented" – and he hoped early phase 3 data could be ready as soon as the end of the year.
There were today 24 coronavirus vaccine candidates in clinical trial. They also included US-based Novovax's NVX-CoV2373.
Ussher said different candidates would emerge at different times, but Oxford's could prove the first cab off the rank. But even with a successful vaccine, there would still be big challenges to overcome.
"Part of the problem is you have to manufacture it. While you might be able to upscale manufacturing, it is still going to fall a long way short of global demand," he said.
"And then you've got to distribute it, which comes with additional challenges."
New Zealand's Government has put $37 million toward a vaccine, $5m for exploring manufacturing a vaccine here and $10m for local research.
One Kiwi collaboration, including Ussher, has been eyeing potential candidates, including a virus-inactivated vaccine approach led by Otago University's Professor Miguel Quiñones-Mateu, and a recombinant spike protein vaccine being developed in Dr Davide Comoletti's Victoria University lab.
Up to $15m would also be steered toward global research collaborations and $7m would go to Gavi - an alliance that distributes vaccines to developing nations.
Alongside the funding, the Government has developed a vaccine strategy, which aimed to secure enough doses of a safe, effective vaccine for New Zealand at the earliest possible time.
A key part of that strategy was building capability for making and distributing a vaccine here if it was needed – something Kiwi biotech company Avalia Immunotherapies has already been exploring with a $100,000 grant.