The outbreak broke out at a Christmas party on 26 November organized by renewable energy company Scatec, which has operations in South Africa, where the variant was first discovered.
Preben Aavitsland, a senior doctor at the Norwegian Institute of Public Health, told Reuters via email: “This party is a much more viral event.
“Our operating hypothesis was that at least half of the 120 participants were infected with the Omicron variant during the party. This makes it currently the largest outbreak of Omicron outside of South Africa.”
In addition to those infected at the party, Aavitsland said, two people living on the west coast of the country and two people being quarantined at Oslo airport have been confirmed to carry the Omicron variant of the coronavirus.
The outbreak prompted the Norwegian government to re-impose some nationwide restrictions to limit the spread of Covid-19.
Across Europe, companies are canceling Christmas party plans due to the arrival of the Omicron variant.
The first person in Oslo confirmed to be infected attended the party, where at least one employee had just returned from South Africa. All attendees were fully vaccinated and had tested negative prior to the event.
“Health authorities have confirmed 12 more cases of Omicron disease in Oslo following the outbreak,” the city of Oslo said in a statement. “So far 13 Omicron cases have been confirmed after sequencing. More cases are expected.”
Health authorities say those infected so far have all had mild symptoms, with no cases requiring hospitalization.
“It is too early to say whether the clinical picture of the disease is different in Omicron infections compared with Delta infections,” Aavitsland said.
“None of the patients had severe symptoms; none required hospitalization. However, this was not unexpected given the young age of the participants.”
Scatec said it followed the advice of authorities throughout the pandemic. It also said it was focused on taking care of its employees and limiting the spread of the virus.