Scientists generally agree that wearing masks reduce the risks of COVID-19 spreading, but the benefit conferred in the K–12 classroom remains unknown. Whether children can wear masks correctly over extended periods is also debatable.
Interpretation of existing evidence by public health agencies worldwide vary. For example, the U.S. Centers for Disease Control and Prevention (CDC) recommendations are considerably more aggressive than that of the World Health Organization (WHO) and the European Centre for Disease Prevention and Control (ECDC). The CDC recommends ‘universal indoor masking by all students (age two and older), staff, teachers, and visitors to K–12 schools, regardless of vaccination status.’ In contrast, WHO does not recommend masks for children under age six and is against their routine use in children ages 6 to 11 because of the ‘potential impact of wearing a mask on learning and psychosocial development.’ The WHO also explicitly counsels against children masking during physical activities to not interfere with their breathing. The ECDC also recommends against masks for children in primary school.
The U.S. CDC has conducted three studies on the effectiveness of masking children in school. Before vaccines became available, a study in elementary schools in Georgia found that masking teachers decreased COVID-19 transmission, but masking students did not. A study of Arizona schools in Maricopa and Pima Counties found that schools without mask mandates were more likely to have COVID-19 outbreaks than schools with mask mandates, but the study had a severe confound. Over 90% of schools without mask mandates were in Maricopa County, with much lower vaccination rates than Pima County. Other study shortcomings included a failure to quantify outbreak size and report student testing protocols. Another study by conducted by the CDC concluded that U.S. counties without mask mandates saw larger increases in pediatric COVID-19 cases after schools opened but failed to account for vaccination rate differences.
Overall, these studies claimed that communities with school mask mandates had less viral transmission than those without. Unfortunately, these same communities had higher background vaccination rates, which severely compromises interpretation. This is a severe confound. A definitive study would need to address this confound by adjusting for the differences in background vaccination rates. The failure of these CDC studies to account for the background vaccination rates is a severe shortcoming undermining the evidence the agency used to make its recommendations.