vaccination; vaccines; age distribution; coronavirus disease 2019/dt [Drug Therapy]; coronavirus disease 2019/pc [Prevention]; cowpox/dt [Drug Therapy]; cowpox/pc [Prevention]; Cowpox virus; drug efficacy; ethnic group; geographic distribution; health care system; human; livestock; low income country; middle income country; note; pandemic; race; smallpox/dt [Drug Therapy]; smallpox/pc [Prevention]; urban area; vaccination refusal; vaccine development; vaccine hesitancy; SARS-CoV-2 vaccine/dt [Drug Therapy]; smallpox vaccine/dt [Drug Therapy]; vaccine; vaccinia vaccine/dt [Drug Therapy]