Ciprofloxacin is not a vaccine, it is an antimicrobial drug (an antibiotic).
Unlike anthrax , you don't need ciprofloxacin to cure plague, many more common antibiotics like amoxicillin or streptomycin will do the job.
Initially caught from a flea bite, plague can be transmitted between people by contact with infected tissue and/or inhaling infected droplets from breathing in the air. Catching it from an airline's air conditioning is unlikely due to the filters but inhaling droplets from people in your immediate area is a serious risk.
Characters are seen entering and exiting Washington Metro (subway) stations externally, but the station interiors and the trains are not DC Metro trains.
You can't get from where Max is running along the C&O Canal to where the van picked him up by just going up a set of steps. That's at least a mile away.