Airborne infection risks of SARS-CoV-2 in U.S. schools and impacts of different intervention strategies

Abstract

The potential airborne transmission of SARS-CoV-2 has triggered concerns as schools continue to reopen and resume in-person instruction during the current COVID-19 pandemic. It is critical to understand the risks of airborne SARS-CoV-2 transmission under different epidemiological scenarios and operation strategies for schools to make informed decisions to mitigate infection risk. Through scenario-based analysis, this study estimates the airborne infection risk of SARS-CoV-2 in 111,485 U.S. public and private schools and evaluates the impacts of different intervention strategies, including increased ventilation, air filtration, and hybrid learning. Schools in more than 90% of counties exhibit infection risk of higher than 1%, indicating the significance of implementing intervention strategies. Among the considered strategies, air filtration is found to be most effective: the school average infection risk when applying MERV 13 is over 30% less than the risk levels correlating with the use of increased ventilation and hybrid learning strategies, respectively. For most schools, it is necessary to adopt combined intervention strategies to ensure the infection risk below 1%. The results provide insights into airborne infection risk in schools under various scenarios and may guide schools and policymakers in developing effective operations strategies to maintain environmental health.

Ventilation strategies to reduce airborne transmission of viruses in classrooms: A systematic review of scientific literature

“…[ 73 ] have tested the impact of different intervention strategies with a MM like increasing the VRs, implementing air filtration, hybrid learning (i.e., part of the students attends lessons at home reducing the number of students in presence), and combined strategies through a scenario-based analysis, with which it was possible to estimate the number of infected people attending schools. Based on the pandemic scenario assumed, implying a greater presence of infected people during the winter, and considering an air rate equal to 2 h −1 as a reference, the authors estimated a probability of contagion equal to 6.8% in winter and 3.8% in summer.…”

“…To sum up, some authors argue that MVS strategies in school environments should be adapted to the school grade [ 73 , 96 ] and their implementation is highly encouraged in small-volume classrooms [ 72 ]. Many authors converge that to reduce cross-infection in different classrooms, MVS strategies should use HEPA or MERV 13 filters and setting VRs around 6–7 ACH [ 73 , 74 , 96 ]. Further strategies for optimizing the risk reduction can be a combination of DV with partitions, APs, UVGI [ 74 ], or a combination of face masks and APs [ 96 ].…”

“… ref. Method Room volume N. students Ventilation strategy Evaluation parameter [ 73 ] MM 111,485 US schools NA VRs (4 ACH) Probability of infection Use of MERV 13 Combined strategies [ 96 ] MM/NM NA 9 VRs (3.4 ACH) Probability of infection Use of MERV 7 and MERV 11 Combined strategies [ 74 ] MM 396 m 3 35 VRs Probability of infection 154.5 m 3 25 Different air distribution systems 600 m 3 96 Use of MERV 13 and HEPA filter Use of AP and UVGI Use of facial mask Combined strategies [ 75 ] MM NA NA VRs Cost-benefit evaluation Use of HEPA filter Installation of air distribution system [ 76 ] MM 150 m 3 (50 m 2 × 3 m) ...…”

“…Mechanical ventilation strategies should consider the grade of the school to assess the right viral emission of children and thus an ad-hoc ventilation [ 96 ]. Based on [ 73 , 74 ], the risk of contagion in a poor ventilated classroom (i.e., assuming 2 ACH provided by a MVS in the MM) is the highest in high schools, followed by middle schools, elementary schools, and kindergartens. This is due to the difference in human pulmonary ventilation which determines the amount of virus in aerosols exhaled by infectious people and inhaled by susceptible people.…”

“… Ref. Ventilation system Strategy type Mathematical method (MM) Numerical method (NM) Full-scale experiment (FSM) [ 70 ] NV AS x [ 71 ] NV AS x [ 72 ] NV AS&VP x [ 73 ] MV VP x [ 74 ] MV VP x [ 75 ] MV VP x [ 76 ] NV&MV AS&VP x [ 77 ] MV VP x [ 78 ] MV VP x [ 79 ] MV VP x [ 80 ] MV VP x …”