A new modelling study from UMC Utrecht shows that a reduction of contacts associated with infection in schools can lead to a significant decrease in the effective reproduction number Re if other measures fail. Such school measures are most effective in the oldest age groups, in higher education and in the oldest groups in secondary schools.

In the fall of 2020, many countries experienced a 2^nd wave of the corona pandemic. Policymakers worldwide are struggling to choose the right mix of measures to control the number of COVID-19 cases while enabling or sustaining social and economic activities. The priority of keeping schools open is high, but the role of schools in the course of the corona epidemic is unclear. Researchers from the Mathematical Modeling Group led by prof. Mirjam Kretzschmar of UMC Utrecht used a mathematical transmission model to analyze the impact of virus dissemination in schools and contact reduction on pandemic management.

Researcher and lead author of the publication dr. Ganna Rozhnova says: “In the fall of 2020, when the number of infections rose again, there was a lot of discussion about reopening or keeping schools closed. Our model shows that if schools had remained closed after the summer holidays - and in the absence of other social distancing measures - the Re would have been reduced from 1.31 in August to 1.18 in November. Hence this would not have prevented the development of the second wave of infections in the fall of 2020. By reducing all contacts in August to the level of the first lockdown, the Re would have been reduced to 0.83.”

Due to limited compliance with the imposed social distancing measures, this decrease was not achieved and the Re was 1.00 in November. The model also shows that if the implemented measures would lead to a maximum reduction of Re to 1.00, closing schools could further reduce Re to 0.84. Looking at age groups, school closure would mean a reduction in Re of 8 percent in children aged 10-20, 5 percent in the 5-10 age group, and reduction would be negligible in children under 5 years of age.

The analysis also shows that a reduction in contacts can already have a significant effect. For example, a reduction in infectious contacts in schools by 30-40 percent can already cause a decrease of Re of 10 percent (against 16 percent with full school closure). Measures are most effective in secondary schools. The use of rapid tests among high school students attending school aims to achieve such an effect.

Co-researcher prof. Marc Bonten, medical microbiologist at UMC Utrecht: “Our analysis shows that the impact of the spread of SARS-CoV-2 in schools depends on the remaining possibilities to reduce non-school-related contacts. If the options for reducing Re with non-school based measures are exhausted or undesirable and Re is still around 1, then reducing contacts that can lead to contamination can have a significant impact on Re, especially if achieved with the oldest age group. "

The researchers used a transmission model adapted to age-specific Dutch data on seroprevalence and hospitalization to estimate the impact of school contacts on the transmission of corona and to assess the effects of measures that reduce the number of contacts that can lead to contamination (including school closure) on different times during the pandemic. They used estimates of the susceptibility to corona in children, adults and the elderly and the reduction of Re through social distancing measures in schools and in the rest of society. Based on these analyzes, they formulated recommendations on when reducing school contact would be enough to achieve pandemic control (Re <1), and what school ages to focus on to maximize virus transmission decline.

Publication

Rozhnova G, Dorp CH van, Bruijning-Verhagen P, Bootsma MCJ, Wijgert JHHM van de, Bonten MJM, Kretzschmar ME. Model-based evaluation of school and non-school-related measures to control the COVID-19 pandemic. Nature Communications, 2021;12:1614