Dutch health authorities said Tuesday that the new COVID-19 variant was present in the Netherlands a week earlier than previously believed and checks are underway to see how far it has spread.

The RIVM National Health and Environment Institute said it “has found the coronavirus variant Omicron in two test samples that had already been taken in the Netherlands… on November 19 and 23.”

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On Monday, Dutch officials said that a couple caught trying to escape from COVID-19 quarantine after testing positive for the coronavirus have been transferred to a hospital where they were being held in isolation

The pair, a Spanish man and Portuguese woman, left the hotel where travelers who tested positive for the virus were staying after arriving at Amsterdam’s Schiphol airport from South Africa.

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The discovery of Omicron, dubbed a “variant of concern” by the World Health Organization, has sparked worries around the world that it could resist vaccinations and prolong the nearly two-year-old COVID-19 pandemic.

Dutch authorities are also seeking to contact and test some 5,000 other passengers who have travelled from South Africa, Botswana, Eswatini, Lesotho, Mozambique, Namibia or Zimbabwe.

In the Netherlands, tougher COVID-19 measures went into effect on Sunday to curb record daily infection rates of more than 20,000 and ease pressure on hospitals.

Read more:

WHO says PCR tests detect Omicron, new COVID-19 variant has higher reinfection risk

Hong Kong expands travel curbs on Omicron fears, Australia reports five cases