Efforts to slow the spread of COVID-19 through non-pharmaceutical interventions and preventive measures such as social-distancing and self-isolation have prompted the widespread closure of primary, secondary, and tertiary schooling in over 100 countries.
Previous outbreaks of infectious diseases have prompted widespread school closings around the world, with varying levels of effectiveness. Mathematical modelling has shown that transmission of an outbreak may be delayed by closing schools. However, effectiveness depends on the contacts children maintain outside of school. School closures appear effective in decreasing cases and deaths, particularly when enacted promptly. If school closures occur late relative to an outbreak, they are less effective and may not have any impact at all. Additionally, in some cases, the reopening of schools after a period of closure has resulted in increased infection rates. As closures tend to occur concurrently with other interventions such as public gathering bans, it can be difficult to measure the specific impact of school closures.
During the 1918-1919 influenza pandemic in the United States, school closures and public gathering bans were associated with lower total mortality rates. Cities that implemented such interventions earlier had greater delays in reaching peak mortality rates. Schools closed for a median duration of 4 weeks according to a study of 43 US cities' response to the Spanish Flu. School closures were shown to reduce morbidity from the Asian flu by 90% during the 1957-58 outbreak, and up to 50% in controlling influenza in the US, 2004-2008.
Multiple countries successfully slowed the spread of infection through school closures during the 2009 H1N1 Flu pandemic. School closures in the city of Oita, Japan, were found to have successfully decreased the number of infected students at the peak of infection; however closing schools was not found to have significantly decreased the total number of infected students. Mandatory school closures and other social distancing measures were associated with a 29% to 37% reduction in influenza transmission rates. Early school closures in the United States delayed the peak of the 2009 H1N1 Flu pandemic. Despite the overall success of closing schools, a study of school closures in Michigan found that "district level reactive school closures were ineffective."
During the swine flu outbreak in 2009 in the UK, in an article titled "Closure of schools during an influenza pandemic" published in the Lancet Infectious Diseases, a group of epidemiologists endorsed the closure of schools in order to interrupt the course of the infection, slow further spread and buy time to research and produce a vaccine. Having studied previous influenza pandemics including the 1918 flu pandemic, the influenza pandemic of 1957 and the 1968 flu pandemic, they reported on the economic and workforce effect school closure would have, particularly with a large percentage of doctors and nurses being women, of whom half had children under the age of 16. They also looked at the dynamics of the spread of influenza in France during French school holidays and noted that cases of flu dropped when schools closed and re-emerged when they re-opened. They noted that when teachers in Israel went on strike during the flu season of 1999-2000, visits to doctors and the number of respiratory infections dropped by more than a fifth and more than two fifths respectively.