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School closures reduced the impact of COVID-19 in most countries but had negative effects in some, Monash University-led research encompassing 74 countries has found.

In Australia the researchers found that school closures probably had a positive impact by reducing SARS-CoV-2 infections, peak hospital occupancy and deaths.

Published in leading international medical journal PLOS Medicine, the study used a mathematical model to simulate the COVID-19 epidemics of 74 countries, incorporating data from 2020-2022 and school closure timelines.

They then simulated an alternative scenario, assuming schools stayed open throughout the study period, focusing on infections, hospitalisations and deaths. It is believed to be the first long-term analysis of its type across diverse settings.

School closures were associated with a beneficial effect on infections in 58 (78 per cent) countries, on deaths in 65 (87 per cent) countries, and on peak hospital occupancy pressure in 72 (97 per cent) countries.

In Australia, school closures are estimated to have reduced the number of COVID-19 deaths by about a quarter, from 2020 to 2022 compared to a scenario where schools had remained fully open.

“We estimated that school closures significantly reduced the COVID-19 burden in most countries but might have increased cumulative mortality in a few cases,” the researchers found. “While school closures were effective in many cases, their overall impact varied widely by setting.”

Lead author Dr Romain Ragonnet, a Monash University School of Public Health and Preventive Medicine infectious diseases modeller, said the Australian results aligned with those of several other countries, where school closures significantly reduced the negative impacts of the initial COVID-19 waves.

“In Australia, we also found that school closures decreased the cumulative number of infections caused by the Delta variant, which is notably more virulent than other variants,” he said.

“This reduction likely explains the observed decreases in hospital occupancy and COVID-19 deaths, particularly since Australia had not yet achieved substantial vaccine coverage when the Delta variant emerged.

“To the best of our knowledge, our study is the first to assess the epidemiological impact of school closures over an extended period, encompassing the emergence of multiple viral strains, the rollout of vaccination programs, and the development of population immunity.

“This is critical, as the overall effectiveness of the intervention was expected to be influenced by all of these factors. Additionally, our study is the first to provide country-specific estimates of the effects of school closures for most countries, offering a comprehensive global perspective.”

Among the findings:

• School closures significantly averted infections in all analysed countries of Southeast Asia and the Indian subcontinent.
• In contrast, the USA and 25 of the 30 European countries were associated with small or negative estimated impacts of school closures on infections and deaths, with estimated median reductions of less than 10 per cent for both indicators.
• In all countries of Central and South America, the model suggested major reductions of peak hospital occupancy pressure due to school closures.
• School closures were estimated to have had a positive impact on infections, deaths and peak hospital occupancy pressure in the five African countries analysed.

Dr Ragonnet said the findings provided evidence-based insights into the effectiveness of school closures as a public health intervention during pandemics.

“We estimated that the intervention led to reductions in SARS-CoV-2 infections, peak hospital occupancy and deaths in most countries,” he said. “However, the study also found that, in a few cases, school closures may have inadvertently increased cumulative mortality, underscoring the complex and context-dependent nature of such interventions.

“Understanding the nuanced impacts of such measures can help inform policymakers in making balanced decisions that consider both the benefits and potential unintended consequences of school closures. “In particular, we highlighted key epidemiological mechanisms that should be considered when making decisions about school closures. These include the potential worsening of the long-term epidemic due to changes in population immunity and the emergence of more virulent future variants, as well as shifts in the age distribution of infections. This is especially important for future pandemic preparedness and response strategies.

“It is crucial to examine the broader consequences of school closures, including their impacts on mental health, other medical conditions, education, and the economy. Even in countries where the intervention was estimated to have a positive effect on COVID-19 disease indicators, a comprehensive, multifactorial assessment is necessary to fully understand the impacts of school closures on populations. Our study represents only one piece of the puzzle.” The analyses were at the national level, even though school closure policies varied between regions. They could only cover a few countries in certain regions, including Africa, due to insufficient data.

“The question of whether school closures were a good policy still lacks a straightforward answer,” the study found. “Even for a single country, the estimated epidemiological effects may differ for various indicators, as illustrated with Indonesia where closures prevented infections but increased COVID-19 mortality.

“Our findings underscore the importance of a nuanced and tailored approach to such interventions, considering both their immediate and longer-term impacts on local epidemics.”

Included countries Argentina, Australia, Austria, Belgium, Bangladesh, Bulgaria, Bosnia and Herzegovina, Bolivia, Brazil, Canada, Chile, Colombia, Costa Rica, Czechia, Germany, Denmark, Ecuador, Egypt, Spain, Finland, France, United Kingdom, Georgia, Greece, Guatemala, Honduras, Croatia, Hungary, Indonesia, India, Ireland, Iraq, Israel, Italy, Jordan, Japan, Kazakhstan, Kenya, Korea, Republic of Lebanon, Sri Lanka, Lithuania, Latvia, Morocco, Moldova, Republic of Mexico, North Macedonia, Myanmar, Malaysia, Netherlands, Nepal, Pakistan, Panama, Peru, Philippines, Poland, Portugal, Paraguay, Romania, Russian, Federation, Saudi Arabia, Serbia, Slovakia, Slovenia, Sweden, Thailand, Turkey, Ukraine, Uruguay, United States, Venezuela, Vietnam, South Africa, Zimbabwe