Commercial Fixed Wing
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Distraction; Confusion; Situational Awareness; Time Pressure
Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
General None Reported / Taken
Company Policy; Environment - Non Weather Related; Human Factors
When I arrived at the airplane for departure I was informed that the FA X had called in sick.  Apparently he had been exposed [to] COVID-19. I discussed the need for a new general declaration with the agent once they had found a replacement. About 30 minutes before push back they gave me the new declaration with all positions filled; and I signed it. About 20 minutes before pushing the agent returned and told me that they had pulled the new crew member off for another flight; and asked me if we could go with XX [number] of FAs. Not catching my error I said yes and asked for a new general declaration; it arrived just before departure time I signed it and we departed shortly thereafter.This was my first flight in over nine months with passengers; I had a discussion with the Lead FA about the FA that had called in sick; and wanted to be sure none of the other FAs had been exposed to him; apparently none had. We also discussed the fact that we would be getting a replacement. I just missed the fact that our duty time would require XY [number of] FAs.For myself having been on leave and away from flying for so long; I need to slow everything down; take a little more time.
Last minute flight attendant sick call and another reassignment. Misunderstood flight attendant minimum requirements. Was unaware that requirements were based on duty day and not flight time. Departed 1 flight attendant undermanned.Last minute changes at a critical time. COVID-19 concerns and maximum limit of XX passengers. We should seek waiver for restricted load passenger flights. Need assistance from dispatch; flight attendants and load to help watch for errors in manning requirements.
Air carrier flight crew reported inadvertently departing with one less Flight Attendant than required for the flight.