New Zealand's COVID vaccine rollout so far has relied mostly on a single supplier - Pfizer.
But 250,000 doses of a vaccine developed by Novavax will arrive in New Zealand on Thursday, COVID-19 Response Minister Chris Hipkins says. It will be used as an alternative to the Pfizer-BioNTech jab but not as a booster.
Trials to date have found NVX-CoV2373, as it's called, is highly effective against the SARS-CoV-2 virus, and perhaps less likely to cause side effects than the Pfizer jab.
Novavax said last month an extended analysis of a late-stage study conducted in the UK showed that its COVID-19 vaccine provided long-term protection against the coronavirus.
Here's what you need to know.
This article was originally published in September and is republished on Wednesday following the announcement of the vaccine becoming available on Thursday.
What is the Novavax COVID-19 vaccine?
NVX-CoV2373 is a "protein-based vaccine candidate engineered from the genetic sequence of the first strain of SARS-CoV-2", according to Novavax. Work on it began in January 2020, around the same time as BioNTech (which would later team up with Pfizer) and Moderna, after the virus' genetic code was sequenced and made available.
The gene for the virus' spike protein is inserted into an insect virus which is used to infect moth cells. The cells produce new spike proteins, which are harvested and put on nanoparticles. Once injected, our immune systems recognise the spike proteins as foreign and mount a defence.
Novavax's vaccine uses what's known as an adjuvant to help boost the immune response - in this case, saponin, a plant-derived chemical.
How is this different to Pfizer's?
The basic technology behind NVX-CoV2373 has been used since the mid-1980s, The Atlantic reported, in vaccines for hepatitis B and whooping cough.
Pfizer and Moderna's vaccine uses a new type of vaccine technology called mRNA - the first to have made it out of the trial phase. Their vaccines don't contain any viral material at all and instead use a piece of code that teaches our cells how to make the spike proteins themselves.
How does Novavax's vaccine stack up?
In its trials, NVX-CoV2373 performed very well - it offered 90 percent protection against symptomatic infection and not a single person amongst those who received it in the phase 3 trial developed severe disease.
The vaccine also worked well against the Alpha variant, which was dominant in the US and Mexico at the time the trial took place. It didn't do so well against Beta in South Africa when it came to stopping infection, but it still successfully prevented serious illness.
What about side-effects?
The Novavax vaccine appeared to trigger fewer mild-to-moderate side effects in its trials than Pfizer. But - as we've discovered with the rapid rollout of Pfizer, Moderna, AstraZeneca and Janssen vaccines across the world, some serious - even deadly - side effects are so rare they don't show up until millions of people have been injected.
The known side effects to date are typical of any vaccine - headaches, muscle pain and tiredness amongst them.
"Protein-subunit vaccines are considered the safest form of vaccines, based on a widely used technology," University of California Berkeley head of infectious diseases Lee Riley said in June.
What are some other advantages and disadvantages?
Novavax says its vaccine can be delivered alongside an influenza vaccine, which isn't recommended for the Pfizer jab.
There has been widespread misinformation about mRNA vaccines, including false claims they can alter patients' DNA. It's been suggested some people hesitant to get an mRNA vaccine might be more likely to accept a vaccine based on more traditional technology, like that made by Novavax.
It takes a lot longer to make the Novavax vaccine than the mRNA offerings - it reportedly takes just minutes to produce as much synthetic mRNA vaccine as traditional techniques produce in a week. Novavax expected to be able to make 150 million doses a month by the end of 2021 - less than the 250 million a month Pfizer expected to make last year.
People who have a serious reaction to the contents of the Pfizer vaccine - typically the lipid nanoparticle it comes in - might fare better with the Novavax vaccine.
Novavax doses can be stored long-term at typical fridge temperatures, making it easier to store and transport than the Pfizer jab, which needs to be kept in specialised ultra-cold freezers until it's ready to be deployed.
Why has it taken so long?
New Zealand signed a provisional deal with Novavax in 2020, alongside orders from AstraZeneca, Janssen and Pfizer. After seeing the rapid rollout and success of the Pfizer jab in the US and Israel, New Zealand opted to use it exclusively for the initial rollout.
Novavax is a much smaller company than some of the other manufacturers. BioNTech - a small German company - realised early on its mRNA technology might work against COVID-19, and sought the assistance of pharma giant Pfizer in March 2020.
Moderna teamed up with the US National Institutes of Health.
Novavax began its in-person research the same week as BioNTech, The Atlantic reported, but didn't team up with a larger partner to speed things along.
Earlier last year there was speculation Novavax could team up with Merck, after the latter's attempt at developing a COVID-19 vaccine was abandoned. It eventually signed up with GlaxoSmithKline, another giant that failed to develop its own jab.
It's also cut deals with other drugmakers in countries like Japan, Poland and India.
Novavax repeatedly delayed seeking approval from US health authorities but finally in late January filed for emergency use authorisation of the shot in American adults.
Hipkins on NZ's Novavax rollout
In a statement on Wednesday, Hipkins said Novavax would be available for people aged over 18.
He said the vaccine requires two doses with a three-week gap in between.
The vaccine hasn't been approved as a booster, he said.
"While the Pfizer vaccine remains the preferred COVID-19 vaccine in New Zealand, Novavax is now available for those people who would prefer, or require, an alternative."
