http://physics.aps.org/story/v12/st22 "...even frigid intergalactic space is awash in microwave photons that would gradually slow a drifting space traveler. The friction occurs because the moving object absorbs more photons at its front surface than at its rear. The object slows from the flow of photons, just as a cyclist is slowed by the wind she feels in her face. (...) In intergalactic space, the slowing of a macroscopic object would only be noticeable over billions of years. In a 1000-degree-Kelvin oven, on the other hand, a water molecule would need less than five months to slow to a standstill, assuming it started out at the oven's temperature."
How about a photon emitted by a distant astronomical object and travelling towards Earth? Will it be gradually slowed down by vacuum friction? Yes it will, and this explains the cosmological redshift. Any redshift or blueshift is due to a shift in the speed of light: