Experts are warning over 40,000 border workers and their families could need a booster shot by November as evidence mounts that their protection against COVID-19 is waning.
"Our essential workers at the borders, their immunity goes away. And we don't know whether they're gonna be protected against infection and transmitting infection," Malaghan Institute immunologist Professor Graham Le Gros told Newshub Nation.
"Until we get everyone jabbed in this country, we are a ticking time bomb."
It's been six months since our first border workers were fully vaccinated with the Pfizer jab and new research shows protection from the vaccine becomes less effective as time goes on.
The Pfizer vaccine's effectiveness drops from 92 percent to 78 percent in just three months, according to an Oxford University study in Britain.
The US Centre for Disease Control found a bigger decline from 91 percent to 66 percent when the Pfizer vaccine is faced with Delta. Other estimates out of Israel are even lower and it's getting worse with time.
"I was horrified by that... it means that we actually have to have a booster shot," said Prof Le Gros.
Auckland University vaccinologist Dr Helen Petousis-Harris is on the Government's vaccine advisory group and says it's important to remember that even a slightly less effective vaccine still provides excellent overall protection.
"It remains very good at preventing sickness. The protection against disease, particularly severe disease, is holding up really well."
"Where we see some decline is in its ability to prevent people getting infected and passing on the virus to others...Certainly by six months there's a clear decline."
The risk at the border is "breakthrough infections" - cases in vaccinated border workers, who can then pass the virus on and take COVID-19 from quarantine to the community.
By November more than 43,000 border workers will have had six months since their second dose. Dr Petousis-Harris agrees with Prof Le Gros - boosters are our best - and only - option.
"The best chance you have in protecting against their ability to pick up the virus and transmit it is going to be in booster shots - we actually don't have anything else in our armory," she said.
National is also advocating for boosters at the border.
"It's clear that our border workers are going to need booster shots," National COVID-19 spokesperson Chris Bishop told Newshub Nation.
"Most other developed nations have ordered hundreds of millions of booster shots - New Zealand hasn't ordered a single one."
It still isn't clear how the latest outbreak made it out of managed isolation - or whether a border worker was involved. Three MIQ workers have now tested positive, but health officials won't say how long it's been since any of them had their second jab.
A Kiwi-made booster is in the works at the Malaghan Institute - but it's at least a year away. Meanwhile the question of boosters for the general public is being debated around the world.
Croatia and Austria will no longer take tourists whose vaccines are more than six months old. Booster programs have begun in Israel, and they'll soon start in the US.
But some health experts want richer nations to wait for the world to catch up first.
"When you start diverting or using resources to come along with a booster shot when you've still got a lot of people unvaccinated, it becomes hard to justify," says Dr Petousis-Harris
Even after six months, two doses of the vaccine gives good protection against illness and death but that may not be enough at the border, where an outbreak is only ever an infection away.
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