Unlike “Airborne”, the manufactures of the PlaneCleanAir filters don’t make any grandiose claims that it will stop colds while traveling. What they do claim, though, is that it will filter out 99.5% of bacteria carried in airplane air vents. The filters attach to most Airbus and Boeing nozzles and not only filter the air, but distribute a wider flow of fresh filtered air in your direction. The filters last for 10 flights and cost $20/piece, plus $7 for the adapter to fit the filter to the air nozzle.
More info here.