In public health, social distancing, also called physical distancing, is a set of non-pharmaceutical interventions or measures intended to prevent the spread of a contagious disease by maintaining a physical distance between people and reducing the number of times people come into close contact with each other. It usually involves keeping a certain distance from others (the distance specified differs from country to country and can change with time) and avoiding gathering together in large groups. By minimising the probability that a given uninfected person will come into physical contact with an infected person, the disease transmission can be suppressed, resulting in fewer deaths. The measures may be used in combination with others, such as good respiratory hygiene, face masks and hand washing. To slow down the spread of infectious diseases and avoid overburdening healthcare systems, particularly during a pandemic, several social-distancing measures are used, including the closing of schools and workplaces, isolation, quarantine, restricting the movement of people and the cancellation of mass gatherings. Drawbacks of social distancing can include loneliness, reduced productivity and the loss of other benefits associated with human interaction. Social distancing measures are most effective when the infectious disease spreads via one or more of the following methods, droplet contact (coughing or sneezing), direct physical contact (including sexual contact), indirect physical contact (such as by touching a contaminated surface), and airborne transmission (if the microorganism can survive in the air for long periods). The measures are less effective when an infection is transmitted primarily via contaminated water or food or by vectors such as mosquitoes or other insects. Authorities have encouraged or mandated social distancing during the COVID-19 pandemic as it is an important method of preventing transmission of COVID-19. COVID-19 is much more likely to spread over short distances than long ones. However, it can spread over distances longer than 2 m (6 ft) in enclosed, poorly ventilated places and with prolonged exposure. The term "social distancing" was not introduced until the 21st century. Social distancing measures have been successfully implemented in several epidemics. In St. Louis, shortly after the first cases of influenza were detected in the city during the 1918 flu pandemic, authorities implemented school closures, bans on public gatherings and other social-distancing interventions. The influenza fatality rates in St. Louis were much less than in Philadelphia, which had fewer cases of influenza but allowed a mass parade to continue and did