SARS-CoV-2 transmission in classroom settings: Effects of mitigation, age, and Delta variant

Abstract

Traditional, in-person classroom settings have been limited during the COVID-19 pandemic due to their potential to transmit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among students, teachers, and other educational workers. Using computational fluid dynamics simulations, mitigation strategies that span approaches using face coverings, various ventilation schemes, air purifiers/cleaners, and desk shields are systematically evaluated in thermally controlled classrooms. Individually, face coverings and source control were the most effective, which was followed by well-designed ventilation systems. The use of desk shields was also studied and appeared to be ineffective. The best mitigation approach is shown to be through multiple measures—using face coverings and ventilation systems combined with air purifiers. The studies were extended to elementary schools and consider Delta variants of SARS-CoV-2. In elementary settings, the reduced pulmonary and viral emission rates of small children are observed to drive reduced transmission rates, to values even lower than those observed with several mitigation methods for classrooms with adults. The Delta variant, with adults, was evaluated by considering an increase in quanta and indicated higher transmission probabilities. These increases are levels that are controllable by increasing the mitigation methods. Results indicate several plans of action for schools to return to in-person schooling in the context of age and new variants.

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

“…In [ 96 ] the authors have evaluated the infection risk of several mitigation strategies (i.e., mask covering, mechanical ventilation, AP, and desk shields) in elementary classroom and high school classroom by combining CFD simulations and the Wells-Riley based equation. From the analysis of the results, the use of masks is the most efficient strategy followed by the adjustment of VRs (from 3.4 h −1 to 7 h −1 ), while the desk shields have a low effectiveness.…”

“…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 ].…”

“…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 ]. Also, CO 2 sensors can serve to estimate the necessary air exchange rate to prevent from contagion [ 72 ].…”

“… 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.…”