Public health has many sub-fields, but usually contains the interdisciplinary classes of epidemiology, biostatistics and health services. Environmental health, neighborhood health, behavioral health, and occupational health are additionally important areas of public health. Health, according to the World Health Organization, is "a state of complete bodily, mental and social well-being and never merely the absence of disease and infirmity". A number of definitions have been used for various functions over time. Public swimming swimming pools must scan proof of vaccination QR codes for entry.…