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Jet engines are designed to contain a fan blade failure, and the engines and airplanes are designed with this type of failure in mind. This is more critical in the modern high-bypass designs with large fans. Pictures from bird strikes sometimes show pretty severe damage, but I don't remember any that actually lost a fan blade.
How often does a jet engine actually lose a fan blade?
This is different from a rotor burst, which is uncontained (like with Qantas Flight 32).
I found the following rather surprising statement in a (probably quite old) University of Southamption document
Rolls-Royce has never had a service failure of conventional fan blades in over 40 million hours of operation, and there have been no service failures of wide-chord blades in over 10 million hours of operation (Baldwin 1993).
In one incident, RB211-535E4 engines on a Boeing 757 were struck by a flock of Canada geese near Chicago – some seven birds, each around 3 kg, were ingested. The wide-chord fan blades withstood the impact, which was some eight times greater than the requirements for certification, and the engine did not have to be shut down in flight.
So far as I know, bodies like the NTSB don't collect statistics on blade failure events.
Fan blade failure isn't unknown. Three widely reported incidents:
1989 January 8, British Midland Airways 92. A fan blade fractured due to aerodynamic flutter.
2016 August 27, Southwest Airlines 3472. Part of a fan blade broke off, after the engine ingested debris.
2018 April 17, Southwest Airlines 1380. A fan blade separated at the root.
Page 4 of a 1997 FAA advisory circular quotes an SAE report of 676 uncontained engine failures from 1969 to 1997, but doesn't discriminate between blade failure and other failures.
Page 19 of a 1991 SAE Report on aircraft engine containment may have the closest answer: high bypass turbofans had 1.12 events per million hours, and 0.56 when excluding fan blade events; subtracting, we get 0.56 fan blade failures per million hours that resulted in uncontained engine failure, for commercial transport during 1976-1983. Blade failures that did not cause uncontainment aren't counted here, so the true number should be somewhat higher. This hundred-page report goes into eye-watering detail.
The failure rate of aircraft engines has reached an all-time low. This means that many flight crews will never face an engine failure during their career$\endgroup$