United Airlines CEO Scott Kirby on Thursday said many more people need to receive coronavirus vaccines before travel demand returns, highlighting difficult months ahead for the industry.

United’s shares were down more than 2% in premarket trading after the airline posted a $1.9 billion loss after the market closed on Wednesday, marking its fourth quarterly loss in a row.

“Until we can put as a society coronavirus in the real view mirror, it’s going to continue to be a tough environment for aviation for everyone who’s involved in travel, tourism and leisure,” Kirby said in an interview with ‘s “Squawk Box.”

The vaccine rollout has been slower than expected, raising questions about when the pandemic will be brought under control.

Kirby said it’s too early to tell when the carrier will break even. Competitor Delta Air Lines last week said it expects to break even by the spring.

“We really need to get a critical mass of people in the country vaccinated and we also need a scientific medical conclusion that it not only protects you from the virus when you get vaccinated but also protects you from transmitting the virus,” said Kirby.