Ryanair missed its targets in December after the spread of Omicron forced governments to reimpose restrictions on international travel.
The business said it had carried 11.3 million passengers in October and 10.2 million in November.
But despite the holidays, just 9.5 million passengers travelled with Ryanair in December, far below its 11 million target.
“The sudden emergence of the Omicron variant and the media hysteria it generated in December, forced many European governments to reimpose travel restrictions in the run-up to Christmas, which significantly weakened peak Christmas and New Year bookings and fares,” the business said.
But Ryanair still saw a strong recovery from the worst parts of the pandemic. During the three last months of 2021, it said, 31.1 million passengers travelled on its planes, nearly four times more than a year earlier.
And it is also showing confidence going into the vital summer season.
This summer Ryanair is selling 14% more tickets than it had in the last summer before Covid, in 2019.
The business said that it expects to carry just under 100 million passengers in its financial year, which ends in March.
This is unchanged from December when the figure was downgraded from more than 100 million.
However, the company is having to discount more tickets to get passengers onboard, so its expected losses have gone from between 100 million euro and 200 million euro (£83 million to £166 million) to a new forecast of between 250 million euro and 450 million euro.
“This outturn is hugely sensitive to any further positive or negative Covid news flow, and so we would caution all shareholders to expect further Covid disruptions before we here in Europe and the rest of the world can finally declare that the Covid crisis is behind us,” the business said.
To sign up for the Nottinghamshire Live newsletter click here
