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A warning there could be hold-ups as people try to download My Vaccine Pass, which will prove they've been vaccinated against the virus.
It will be a QR code that can be shown digitally or printed out.
Once the traffic light system is in place, the pass will give double-jabbed people access to places like churches, restaurants, gyms, bars and sporting events.
Covid-19 Response Minister Chris Hipkins told Mike Hosking 200 vaccine certificates can be produced per second.
“Which is pretty good, by industry standards, so I’m told. But if everybody tries to do it at the same time, there may be a few delays, there could be up to 3 million people trying to do it all at the same time.”