The COVID-19 Omicron variant likely spread across western Europe for over a week before it was identified on Nov. 24 in South Africa, Dutch health authorities revealed on Tuesday (Nov. 30). Officials at the RIVM Health Institute said samples of the new variant were found in two COVID-19 cases in the Netherlands dating back to Nov. 19 and Nov. 23.

“It is not yet clear whether the people concerned [in the earlier cases] have also been to southern Africa,” the RIVM said Tuesday, adding that the individuals who tested positive for the Omicron variant and their local health services have been informed.

“In the coming period, various studies will be conducted into the distribution of the Omicron variant in the Netherlands,” the institute added. The RIVM will also re-examine other previous COVID-19 test results to check for the variant.

Belgian and German health officials also said the sample tests confirm the variant was in western Europe before South African scientists detected it last week.

No Omicron cases have been reported in the United States yet, but the strain has spread to around 20 other countries. On Tuesday, Canada reported six cases of the variant; following reports from Brazil, France, China, Spain, Germany, Sweden, Japan, Australia and more.

President Joe Biden has already restricted travel to certain countries to prevent the spread of the strain, but said he will not reimpose lockdown policies.

“We have the best vaccine in the world, the best medicines, the best scientists, and we’re learning more every single day,” he said. “We will fight this variant with scientific and knowledgeable action and speed — not chaos and confusion.”

On Monday (Nov. 29), the Centers for Disease Control and Prevention expanded its vaccine guidance, recommending all adults to get the COVID-19 vaccine booster shot. New York City Mayor Bill de Blasio also told locals to prepare for the return of indoor mask policies.

“We’re telling you to get those masks back on now,” he said. “It’s smart to do.”