Travellers carrying certificates that say they do not have Covid-19 are later testing positive when they settle in to a managed isolation facility.
Yesterday the Ministry of Health reported eleven new cases in managed isoaltion - ten of those arriving on the same flight.
Reports say travellers are being offered "fake negative" test certificates.
Dr Ashley Bloomfield has directed officials to investigate the pre-departure testing regime.
So is pre-departure testing really working?
Professor Michael Baker spoke to Susie Ferguson.