A COVID outbreak has occurred in Oslo, Norway, after more than 50 people were infected after attending an office Christmas party.

The Norwegian Institute of Public Health confirmed one case of the Omicron variant from the party, saying on Thursday that it had not determined exactly how many were infected with the variant, but recommended that all participants of the event be tested.

“The outbreak in Oslo, with participants from several other municipalities, is large, with many infected people and their close contacts being followed up,” the agency said.

The majority of the party attendees were vaccinated, health officials said.

According to the Norwegian state news outlet NRK, doctors said that of the 50 to 60 people that have tested positive for the virus, the infections were not Delta variant cases with “clear clues” and a “strong possibility” they were all Omicron variant infections.

Tine Ravlo, an assistant chief infection control doctor in Oslo’s Frogner district, said a preliminary screening indicated that the cases’ samples were likely Omicron, as reported by The Independent.

The news outlet also said that one party attendee has been to South Africa recently. South Africa was where the first case of the Omicron variant was first detected last week.

If the reported cases of the Omicron variant at the party are all Omicron variant infections, it will be considered the largest outbreak of the COVID strain in the world to date.

Norway has reported at least three cases of the Omicron variant as of Friday.

Christmas tree
A festively decorated Christmas tree standing in a farm's garden is slightly covered in snow in southern Germany on Dec. 8, 2014. Karl-Josef Hildenbrand/AFP/Getty Images