full list after big outbreak

Researchers have released new data from a large omicron outbreak in Norway that offers a window into how the variant behaves among highly vaccinated populations. The outbreak was attributed to a Christmas party and a pre-party in Oslo held on November 26. Here are some of the key findings, according to the research recently published in the open-access journal Eurosurveillance:

Vaccination status and transmissibility

Researchers interviewed 111 out of 117 attendees. Among those who participated in the interviews, the median age was 38, 43% were women, and 89% had received two doses of an mRNA vaccine.

Of the participants, 66 had confirmed cases of COVID-19 and 15 had probable cases. Most of the infected were fully vaccinated; however, none of the attendees reported having a booster shot. They also had negative tests taken within one to two days of the event. 

“The total attack rate for the Omicron variant was 74%,” according to the study, consistent with other research showing that omicron is likely more transmissible that earlier variants and that vaccines are less effective in preventing its spread.


All cases but one were symptomatic, and 91% of infected people reported at least three symptoms. The median incubation period was three days. Below are the most commonly reported symptoms:

  • Cough (83%)
  • Runny/stuffy nose (78%) 
  • Fatigue/lethargy (74%)
  • Sore throat (72%) 
  • Headache (68%) 
  • Muscle pain (58%)
  • Fever (54%)
  • Sneezing (43%) 

You can see the full symptoms breakout page here. Interestingly, some symptoms commonly associated with COVID-19, such as reduced sense of smell, were not widely reported.  

Severe outcomes

According to the study, none of the cases required hospitalizations as of December 13. “However, we cannot exclude that vaccination has reduced the risk of serious illness,” the researchers wrote. It’s still early days given that the variant was only detected last month, and what we know about omicron now is likely to evolve and change as rapidly as the variant seems to be spreading.