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“We all have choices to make that affect our likelihood of contracting infectious disease: whether to holiday in exotic countries; whom to let our children play with; whether we travel on crowded public transport. When we are ill, other choices we make affect our likelihood of transmitting disease to others: whether we cancel the much-anticipated catch-up with our friends; whether we keep our children home from school; whether we cover our mouths when we cough. The crucial decision on whether we vaccinate ourselves and our dependents can only be taken ahead of time. It affects our chances not only of catching but also of transmitting diseases. Some of these decisions are inexpensive, making their adoption straightforward. It costs nothing to sneeze into a tissue or a handkerchief. Simply washing your hands frequently and carefully has been shown to reduce the effective reproduction numbers of respiratory illnesses such as flu by as much as three-quarters. For some diseases, this might be enough to take us below the threshold value of R0, so that an infectious disease cannot break out.”
― Kit Yates, The Math of Life and Death: 7 Mathematical Principles That Shape Our Lives