How did 10% of passengers to Holland from South Africa arrive with Covid when they all had NEGATIVE tests?

How did 10% of passengers to Holland from South Africa arrive with Covid when they all had NEGATIVE tests? Alarm as suspected cases of Omicron are reported in Germany, Australia and Czech Republic alongside confirmed UK and Belgium cases

• Around 600 passengers arrived on two planes in Schipol Airport, Amsterdam, from Johannesburg  yesterday
• Passengers have been put in quarantine hotels while authorities investigate whether they have been infected
• Countries across Europe closed their borders to countries in southern Africa yesterday to combat the variant

It raises the prospect that tests are not being performed correctly for travellers in South Africa, fraudulent tests are being provided or lateral flow tests may be less able to detect the Omicorn variant.  All 61 passengers are said to have been asymptomatic, suggesting that the Omicron variant is not of as much concern as its being made out to be. 

South Africa’s medical chief Dr. Angelique Coetzee described the panic as a “storm in a teacup,” adding that she had only seen “very very mild cases” of the variant so far.