Well... I honestly don't know how much use a paper filter would be against virus and even bacterial infection... though it would definitely reduce the amount of airborne pollutants that you would breath... I suppose most airborne viruses are carried via water droplets, and for sure, the mask would reduce the number you breath...
But I remember reading somewhere that most infections are actually spread via physical contact... i.e. from face to hand to object to hand to face... Wash your hands :-)