Hong Kong airline Cathay Pacific said it fired staff after a "serious breach" of overseas-layover rules.
The South China Morning Post reported that they were three pilots who were infected during a Frankfurt layover.
Airline staff and other close contacts also had to quarantine, the Post said.
The Hong Kong airline Cathay Pacific fired three pilots who were infected with COVID-19 during a layover in Germany, the South China Morning Post reported.
The airline said in a statement on Thursday that it carried out an investigation after COVID-19 cases were found among its staff.
It said, according to the Post: "After investigation into these cases, regrettably, the findings indicate a serious breach of requirements during crew overseas layovers."
"The individuals concerned are no longer employed by Cathay Pacific."
It did not specify what the breach was.
The Post reported that three cargo pilots were fired, and that they were infected while in Frankfurt, Germany.
The airline said in its statement that it believed there were no more similar cases, saying: "We believe these cases are isolated incidents."
More than 150 employees of the airline had to be quarantined because of the three cases, the Post reported, and other close contacts also were put in a government isolation facility.
Cathay Pacific requires crew to be fully vaccinated.
Hong Kong is pursuing a zero-COVID strategy, and has enforced strict immigration and quarantine rules as part of it.