Hospital staff in Spain held a Christmas party, and 68 ICU nurses later tested positive for COVID-19.
A total of 173 people attended. Authorities said they are still confirming the source of infection.
Everyone had presented a negative antigen test or had a booster COVID-19 shot, Reuters reported.
At least 68 ICU nurses at a Spanish hospital tested positive for COVID-19 after they went to their hospital's Christmas party, according to multiple reports.
The regional government in Spain's Andalusia region said on Monday that the staff worked at the University Regional Hospital in the city of Malaga, Reuters reported.
It said that the source of the infections was still being investigated, but that the nurses had all gone to the party on December 1, according to Reuters.
A total of 173 people were at the party, Reuters reported.
The Spanish newspaper El País reported that the party was at a restaurant in the city.
It is not clear what variant of the virus the nurses were infected with. Those who were infected were also showing mild symptoms, Reuters reported.
Everyone who attended the party had presented a negative antigen test or had their booster coronavirus vaccine, Reuters reported.
Antigen tests are faster and cheaper than some other types of COVID-19 test, like PCR tests, but they are not as accurate and can sometimes display a negative result even if the person has the virus. However, public health experts say the tests still play a vital role as they are accessible and still catch many coronavirus cases.
Vaccines greatly reduce the chances of being infected by the coronavirus, but they do not remove the risk entirely.
People who are vaccinated are also more likely to experience mild symptoms and are greater protected against severe illness and death. Vaccinated people are also less likely to spread the virus.
Any hospital staff who tested positive have been isolated, El País reported. The hospital said it has managed to get their shifts covered, the report said.
Spain has identified seven cases of the Omicron variant.