Social distancing has goal minimization
Definition
The American Centers for Disease Control and Prevention (CDC) have described social distancing as a set of "methods for reducing frequency and closeness of contact between people in order to decrease the risk of transmission of disease". During the 2009 swine flu pandemic the WHO described social distancing as "keeping at least an arm's length distance from others, [and] minimizing gatherings". During the COVID-19 pandemic, the CDC defined social distancing as "remaining out of congregate settings, avoiding mass gatherings, and maintaining distance (approximately six feet or two meters) from others when possible".Social distancing, combined with the use of face masks, good respiratory hygiene and hand washing, is considered the most feasible way to reduce or delay a pandemic.SARS 2003
During the SARS outbreak of 2003, social distancing measures were implemented, such as banning large gatherings, closing schools and theaters, and other public places, supplemented public health measures such as finding and isolating affected people, quarantining their close contacts, and infection control procedures. This was combined with the wearing of masks for certain people. During this time in Canada, "community quarantine" was used to reduce transmission of the disease with moderate success.Theoretical basis
From the perspective of epidemiology, the basic goal behind social distancing is to decrease the effective reproduction number, 
  
    
      R
      
        e
      
    
    R_{e}
   or 
  
    R
    R
  , which in the absence of social distancing would equate to the basic reproduction number, i.e. the average number of secondary infected individuals generated from one primary infected individual in a population where all individuals are equally susceptible to a disease. In a basic model of social distancing, where a proportion 
  
    f
    f
   of the population engages in social distancing to decrease their interpersonal contacts to a fraction 
  
    a
    a
   of their normal contacts, the new effective reproduction number 
  
    R
    R
   is given by:
Where the value of 
  
    R
    R
   can be brought below 1 for sufficiently long, containment is achieved, and the number infected should decrease.For any given period of time, the growth in the number of infections can be modeled as:
where: