Herd immunity is referred to as the resistance of a population to the spread of a contagious infectious disease to which a large number of the population are immune to the disease, these are achieved through immunization often called vaccination.
Vaccination program have been successful against many infectious diseases that once killed, crippled, or incapacitated large number of members of a population.
The further the light moves from the plant, the fewer oxygen bubbles are produced by photosynthesis. The intensity of light at different distances from a light source can be described by the inverse square law.