The bases were closed for winter, resulting in 135 people being laid off.
The airline has agreed to buy 75 Boeing 737 Max aircraft, but says any passengers with safety concerns can be moved to the next available flight on an older model.
Group CEO of Ryanair Michael O'Leary says how soon Cork and Shannon reopen will depend on the Government's response.
"They're definitely going to come back. I mean the real challenge for the Irish government is how fast are they going to come back, you know. We're calling for them to roll out the vaccines quickly in the first quarter of next year. We need to see short term discounts at Cork, Shannon and Dublin airports for the summer of '21 of the winter '21, so that we can pass on these lower fares and get visitors back into Ireland."
