SARS-CoV-2 Incidence in K-12 School Districts with Mask-Required Versus Mask-Optional Policies - Arkansas, August-October 2021

Measures implemented in the school setting to contain the COVID-19 pandemic

BACKGROUND

More than 767 million coronavirus 2019 (COVID-19) cases and 6.9 million deaths with COVID-19 have been recorded as of August 2023. Several public health and social measures were implemented in schools to contain the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and prevent onward transmission. We built upon methods from a previous Cochrane review to capture current empirical evidence relating to the effectiveness of school measures to limit SARS-CoV-2 transmission.

OBJECTIVES

To provide an updated assessment of the evidence on the effectiveness of measures implemented in the school setting to keep schools open safely during the COVID-19 pandemic.

SEARCH METHODS

We searched the Cochrane COVID-19 Study Register, Educational Resources Information Center, World Health Organization (WHO) COVID-19 Global literature on coronavirus disease database, and the US Department of Veterans Affairs Evidence Synthesis Program COVID-19 Evidence Reviews on 18 February 2022.

SELECTION CRITERIA

Eligible studies focused on measures implemented in the school setting to contain the COVID-19 pandemic, among students (aged 4 to 18 years) or individuals relating to the school, or both. We categorized studies that reported quantitative measures of intervention effectiveness, and studies that assessed the performance of surveillance measures as either 'main' or 'supporting' studies based on design and approach to handling key confounders. We were interested in transmission-related outcomes and intended or unintended consequences.

DATA COLLECTION AND ANALYSIS

Two review authors screened titles, abstracts and full texts. We extracted minimal data for supporting studies. For main studies, one review author extracted comprehensive data and assessed risk of bias, which a second author checked. We narratively synthesized findings for each intervention-comparator-outcome category (body of evidence). Two review authors assessed certainty of evidence.

MAIN RESULTS

The 15 main studies consisted of measures to reduce contacts (4 studies), make contacts safer (7 studies), surveillance and response measures (6 studies; 1 assessed transmission outcomes, 5 assessed performance of surveillance measures), and multicomponent measures (1 study). These main studies assessed outcomes in the school population (12), general population (2), and adults living with a school-attending child (1). Settings included K-12 (kindergarten to grade 12; 9 studies), secondary (3 studies), and K-8 (kindergarten to grade 8; 1 study) schools. Two studies did not clearly report settings. Studies measured transmission-related outcomes (10), performance of surveillance measures (5), and intended and unintended consequences (4). The 15 main studies were based in the WHO Regions of the Americas (12), and the WHO European Region (3). Comparators were more versus less intense measures, single versus multicomponent measures, and measures versus no measures. We organized results into relevant bodies of evidence, or groups of studies relating to the same 'intervention-comparator-outcome' categories. Across all bodies of evidence, certainty of evidence ratings limit our confidence in findings. Where we describe an effect as 'beneficial', the direction of the point estimate of the effect favours the intervention; a 'harmful' effect does not favour the intervention and 'null' shows no effect either way. Measures to reduce contact (4 studies) We grouped studies into 21 bodies of evidence: moderate- (10 bodies), low- (3 bodies), or very low-certainty evidence (8 bodies). The evidence was very low to moderate certainty for beneficial effects of remote versus in-person or hybrid teaching on transmission in the general population. For students and staff, mostly harmful effects were observed when more students participated in remote teaching. Moderate-certainty evidence showed that in the general population there was probably no effect on deaths and a beneficial effect on hospitalizations for remote versus in-person teaching, but no effect for remote versus hybrid teaching. The effects of hybrid teaching, a combination of in-person and remote teaching, were mixed. Very low-certainty evidence showed that there may have been a harmful effect on risk of infection among adults living with a school student for closing playgrounds and cafeterias, a null effect for keeping the same teacher, and a beneficial effect for cancelling extracurricular activities, keeping the same students together and restricting entry for parents and caregivers. Measures to make contact safer (7 studies) We grouped studies into eight bodies of evidence: moderate- (5 bodies), and low-certainty evidence (3 bodies). Low-certainty evidence showed that there may have been a beneficial effect of mask mandates on transmission-related outcomes. Moderate-certainty evidence showed full mandates were probably more beneficial than partial or no mandates. Evidence of a beneficial effect of physical distancing on risk of infection among staff and students was mixed. Moderate-certainty evidence showed that ventilation measures probably reduce cases among staff and students. One study (very low-certainty evidence) found that there may be a beneficial effect of not sharing supplies and increasing desk space on risk of infection for adults living with a school student, but showed there may be a harmful effect of desk shields. Surveillance and response measures (6 studies) We grouped studies into seven bodies of evidence: moderate- (3 bodies), low- (1 body), and very low-certainty evidence (3 bodies). Daily testing strategies to replace or reduce quarantine probably helped to reduce missed school days and decrease the proportion of asymptomatic school contacts testing positive (moderate-certainty evidence). For studies that assessed the performance of surveillance measures, the proportion of cases detected by rapid antigen detection testing ranged from 28.6% to 95.8%, positive predictive value ranged from 24.0% to 100.0% (very low-certainty evidence). There was probably no onward transmission from contacts of a positive case (moderate-certainty evidence) and replacing or shortening quarantine with testing may have reduced missed school days (low-certainty evidence). Multicomponent measures (1 study) Combining multiple measures may have led to a reduction in risk of infection among adults living with a student (very low-certainty evidence).

AUTHORS' CONCLUSIONS

A range of measures can have a beneficial effect on transmission-related outcomes, healthcare utilization and school attendance. We rated the current findings at a higher level of certainty than the original review. Further high-quality research into school measures to control SARS-CoV-2 in a wider variety of contexts is needed to develop a more evidence-based understanding of how to keep schools open safely during COVID-19 or a similar public health emergency.

What is the specific role of schools and daycares in COVID-19 transmission? A final report from a living rapid review

Due to rapidly evolving conditions, the question of how to safely operate schools and daycares remained a top priority throughout the COVID-19 pandemic. In response to growing and changing evidence, the National Collaborating Centre for Methods and Tools in Canada maintained a living rapid review on the role of schools and daycares in COVID-19 transmission to guide evidence-informed decision making. This Review presents the final iteration of this living rapid review. 31 sources were searched until Oct 17, 2022. In the final version, eligible studies reported data from Jan 1, 2021 onward on transmission of COVID-19 in school or daycare settings, the effect of infection prevention and control measures on transmission, or the effect of operating schools or daycares on community-level COVID-19 rates. As a rapid review, titles and abstracts were screened by a single reviewer with artificial intelligence integrated into later versions. Full-text screening, data extraction, and critical appraisal were completed by one reviewer and checked by a second reviewer. The Johanna Briggs Institute tools were used for critical appraisal. The certainty of evidence was assessed using the Grading of Recommendations Assessment, Development, and Evaluation approach, and results were synthesised narratively. Three citizen partners provided input for the final interpretation. This final update includes 73 primary studies. Secondary attack rates were low within school settings when infection prevention and control measures were in place (moderate certainty). Masks might reduce transmission, test-to-stay policies might not increase transmission risk compared with mandatory quarantine, cohorting and hybrid learning might make little to no difference in transmission (low certainty), and the effect of surveillance testing within schools remained inconclusive (very low certainty). Findings indicate that school settings do not substantially contribute to community incidence, hospitalisations, or mortality (low certainty). This living review provides a synthesis of global evidence for the role of schools and daycares during COVID-19, which might be helpful in future pandemics.

COVID-19-Related School Closures, United States, July 27, 2020-June 30, 2022

As part of a multiyear project that monitored illness-related school closures, we conducted systematic daily online searches during July 27, 2020-June 30, 2022, to identify public announcements of COVID-19-related school closures (COVID-SCs) in the United States lasting >1 day. We explored the temporospatial patterns of COVID-SCs and analyzed associations between COVID-SCs and national COVID-19 surveillance data. COVID-SCs reflected national surveillance data: correlation was highest between COVID-SCs and both new PCR test positivity (correlation coefficient [r] = 0.73, 95% CI 0.56-0.84) and new cases (r = 0.72, 95% CI 0.54-0.83) during 2020-21 and with hospitalization rates among all ages (r = 0.81, 95% CI 0.67-0.89) during 2021-22. The numbers of reactive COVID-SCs during 2020-21 and 2021-22 greatly exceeded previously observed numbers of illness-related reactive school closures in the United States, notably being nearly 5-fold greater than reactive closures observed during the 2009 influenza (H1N1) pandemic.

Observed Mask Use in Kindergarten Through Grade 12 Schools in Georgia-Fall, 2021

BACKGROUND

Universal masking, with additional layered prevention strategies, was an essential tool for limiting the transmission of SARS-CoV-2 and ensuring a safe return to in-person learning for kindergarten through 12th grade (K-12) students and staff. Few studies have examined mask adherence in this setting and none have described types of masks worn or locations of mask adherence. This project sought to assess mask adherence, types worn, and location of mask adherence in K-12 settings.

METHODS

This study used direct in-person observations to measure the proportion of persons wearing masks correctly; type of masks worn; and location of mask adherence in 19 K-12 schools in Georgia.

RESULTS

A total of 16,222 observations were conducted. Among those observed, 85.2% wore masks, with 80.3% wearing the mask correctly. Persons in high school were less likely to wear masks correctly. Correct mask use was most often observed among persons wearing N95-type masks. The prevalence of persons wearing masks correctly in transitional spaces was 5% higher than in congregate spaces.

CONCLUSION

In K-12 schools with a universal masking policy, correct mask adherence was high among individuals. Examining adherence to recommended prevention measures can provide K-12 schools feedback to inform targeted messaging and policies during future disease outbreaks.

Evaluation of "Test to Return" after COVID-19 Diagnosis in a Massachusetts Public School District

BACKGROUND

Per Centers for Disease Control and Prevention guidance, students with COVID-19 may end isolation after 5 days if symptoms are improving; some individuals may still be contagious. Rapid antigen testing identifies possibly infectious virus. We report on a test-to-return (TTR) program in a Massachusetts school district to inform policy decisions about return to school after COVID-19.

METHODS

During the 2021-2022 Omicron BA.1 surge, students with COVID-19 could return on day 6-10 if they met symptom criteria and had a negative rapid test; students with positive rapid tests and those who declined TTR remained isolated until day 11. TTR positivity rates were compared by grade level, vaccination status, symptom status, and day of infection.

RESULTS

31.4% of students had a positive TTR rapid test; there were no differences by grade or vaccination status. Ever-symptomatic students were more likely to have a positive rapid test (75/174 [43.1%] vs 18/104 [17.3%]). For ever-symptomatic students, TTR positivity decreased by day of infection.

CONCLUSIONS

A substantial proportion of students may still be contagious 6 days after onset of COVID-19 infection. TTR programs may increase or reduce missed school days, depending on when return is otherwise allowed (day 6 or 11). The impact of TTR programs on school-associated transmission remains unknown.

Prevalence and Risk Factors for School-Associated Transmission of SARS-CoV-2

Importance

School-associated SARS-CoV-2 transmission is described as uncommon, although the true transmission rate is unknown.

Objective

To identify the SARS-CoV-2 secondary attack rate (SAR) in schools and factors associated with transmission.

Design, Setting, and Participants

This cohort study examined the risk of school-based transmission of SARS-CoV-2 among kindergarten through grade 12 students and staff in 10 Massachusetts school districts during 2 periods: fall 2020/spring 2021 (F20/S21) and fall 2021 (F21). School staff collected data on SARS-CoV-2 index cases and school-based contacts, and SAR was defined as the proportion of contacts acquiring SARS-CoV-2 infection.

Exposure

SARS-CoV-2.

Main Outcomes and Measures

Potential factors associated with transmission, including grade level, masking, exposure location, vaccination history, and Social Vulnerability Index (SVI), were analyzed using univariable and multivariable logistic regression models.

Results

For F20/S21, 8 school districts (70 schools, >33 000 students) were included and reported 435 index cases (151 staff, 216 students, and 68 missing role) with 1771 school-based contacts (278 staff, 1492 students, and 1 missing role). For F21, 5 districts (34 schools, >18 000 students) participated and reported 309 index cases (37 staff, 207 students, and 65 missing role) with 1673 school-based contacts (107 staff and 1566 students). The F20/S21 SAR was 2.2% (lower bound, 1.6%; upper bound, 26.7%), and the F21 SAR was 2.8% (lower bound, 2.6%; upper bound, 7.4%). In multivariable analysis, during F20/S21, masking was associated with a lower odds of transmission compared with not masking (odds radio [OR], 0.12; 95% CI, 0.04-0.40; P < .001). In F21, classroom exposure vs out-of-classroom exposure was associated with increased odds of transmission (OR, 2.47; 95% CI, 1.07-5.66; P = .02); a fully vaccinated vs unvaccinated contact was associated with a lower odds of transmission (OR, 0.04; 95% CI, 0.00-0.62; P < .001). In both periods, a higher SVI was associated with a greater odds of transmission.

Conclusions and Relevance

In this study of Massachusetts schools, the SAR for SARS-CoV-2 among school-based contacts was low during 2 periods, and factors associated with transmission risk varied over time. These findings suggest that ongoing surveillance efforts may be essential to ensure that both targeted resources and mitigation practices remain optimal and relevant for disease prevention.

Reflections From School Communities in Underserved Populations on Childhood COVID-19 Vaccination

OBJECTIVES

Outbreaks in vaccine-preventable diseases among children have increased, primarily among under- or unvaccinated subgroups. The influence and interaction of a child's school community on parental health care decisions, such as vaccination, has not been explored. Our study examined childhood coronavirus disease 2019 (COVID-19) vaccine hesitancy within the context of school communities.

METHODS

This study combines data from 4 independent research studies funded by the National Institutes of Health Rapid Acceleration of Diagnostics Underserved Populations Return to School Initiative. We examined focus group data to better understand the apprehension surrounding parental and child COVID-19 vaccination among underserved school populations.

RESULTS

Across all study sites, 7 main themes emerged with regard to COVID-19-related vaccination concerns for children: (1) potential side effects, (2) vaccine development, (3) misinformation (subthemes: content of vaccine and negative intent of the vaccine), (4) vaccine effectiveness, (5) timing of vaccine administration/availability for children, (6) fear of needles, and (7) mistrust.

CONCLUSIONS

School settings offered unique access to youth and family perspectives in underserved communities. Our studies highlighted several factors contributing to COVID-19 vaccine hesitancy in school communities, which align with existing literature on vaccine hesitancy. These concerns centered primarily on potential harm of vaccines, as well as misinformation, mistrust, and timing of vaccines. Related recommendations for increasing vaccination rates are provided. Developing specific strategies that address parent and child concerns will be critical to reducing health inequities related to COVID-19 vaccination.

The effect of activity and face masks on exhaled particles in children

Importance

Despite the high burden of respiratory infections among children, the production of exhaled particles during common activities and the efficacy of face masks in children have not been sufficiently studied.

Objective

To determine the effect of type of activity and mask usage on exhaled particle production in children.

Methods

Healthy children were asked to perform activities that ranged in intensity (breathing quietly, speaking, singing, coughing, and sneezing) while wearing no mask, a cloth mask, or a surgical mask. The concentration and size of exhaled particles were assessed during each activity.

Results

Twenty-three children were enrolled in the study. Average exhaled particle concentration increased by intensity of activity, with the lowest particle concentration during tidal breathing (1.285 particles/cm3 [95% CI 0.943, 1.627]) and highest particle concentration during sneezing (5.183 particles/cm3 [95% CI 1.911, 8.455]). High-intensity activities were associated with an increase primarily in the respirable size (≤ 5 µm) particle fraction. Surgical and cloth masks were associated with lower average particle concentration compared to no mask (P = 0.026 for sneezing). Surgical masks outperformed cloth masks across all activities, especially within the respirable size fraction. In a multivariable linear regression model, we observed significant effect modification of activity by age and by mask type.

Interpretation

Similar to adults, children produce exhaled particles that vary in size and concentration across a range of activities. Production of respirable size fraction particles (≤ 5 µm), the dominant mode of transmission of many respiratory viruses, increases significantly with coughing and sneezing and is most effectively reduced by wearing surgical face masks.

Influence of Mask Wearing during COVID-19 Surge and Non-Surge Time Periods in Two K-12 Public School Districts in Georgia, USA

BACKGROUND

Into the third year of the COVID-19 pandemic and the second year of in-person learning for many K-12 schools in the United States, the benefits of mitigation strategies in this setting are still unclear. We compare COVID-19 cases in school-aged children and adolescents between a school district with a mandatory mask-wearing policy to one with an optional mask-wearing policy, during and after the peak period of the Delta variant wave of infection.

METHODS

COVID-19 cases during the Delta variant wave (August 2021) and post the wave (October 2021) were obtained from public health records. Cases of K-12 students, stratified by grade level (elementary, middle, and high school) and school districts across two counties, were included in the statistical and spatial analyses. COVID-19 case rates were determined and spatially mapped. Regression was performed adjusting for specific covariates.

RESULTS

Mask-wearing was associated with lower COVID-19 cases during the peak Delta variant period; overall, regardless of the Delta variant period, higher COVID-19 rates were seen in older aged students.

CONCLUSION

This study highlights the need for more layered prevention strategies and policies that take into consideration local community transmission levels, age of students, and vaccination coverage to ensure that students remain safe at school while optimizing their learning environment.

Children's moral reasoning about self- versus other-benefiting public health measures

The COVID-19 pandemic has introduced novel public health measures such as masking and social distancing. In adults, framing these behaviors as benefiting others versus the self has been shown to affect people's perceptions of public health measures and willingness to comply. Here we asked whether self- versus other-oriented frames of novel public health measures influence children's endorsement and moral reasoning. Children aged 5 to 10 years viewed hypothetical dilemmas of aliens in which we manipulated the frame (other-oriented or self-oriented) of the prevention behavior and the severity (high or low) of the potential harm. Across two studies (Study 1: N = 48; Study 2: N = 61), results showed that across ages framing the behaviors as other-oriented, but not self-oriented, yielded more positive ratings of individuals who followed the public health measures and more negative ratings of those who did not. Across both frames, children generally endorsed these public health measures when the severity was high. Children used more moralizing concepts in other-oriented frames and were more critical of intentional transgressions over accidental transgressions, demonstrating further evidence that other-oriented frames induce moral reasoning. We discuss the theoretical and practical implications of these framing effects for sociomoral reasoning and action.

The Influence of Ventilation Measures on the Airborne Risk of Infection in Schools: A Scoping Review

OBJECTIVES

To review the risk of airborne infections in schools and evaluate the effect of intervention measures reported in field studies.

BACKGROUND

Schools are part of a country's critical infrastructure. Good infection prevention measures are essential for reducing the risk of infection in schools as much as possible, since these are places where many individuals spend a great deal of time together every weekday in a small area where airborne pathogens can spread quickly. Appropriate ventilation can reduce the indoor concentration of airborne pathogens and reduce the risk of infection.

METHODS

A systematic search of the literature was conducted in the databases Embase, MEDLINE, and ScienceDirect using keywords such as school, classroom, ventilation, carbon dioxide (CO2) concentration, SARS-CoV-2, and airborne transmission. The primary endpoint of the studies selected was the risk of airborne infection or CO2 concentration as a surrogate parameter. Studies were grouped according to the study type.

RESULTS

We identified 30 studies that met the inclusion criteria, six of them intervention studies. When specific ventilation strategies were lacking in schools being investigated, CO2 concentrations were often above the recommended maximum values. Improving ventilation lowered the CO2 concentration, resulting in a lower risk of airborne infections.

CONCLUSIONS

The ventilation in many schools is not adequate to guarantee good indoor air quality. Ventilation is an important measure for reducing the risk of airborne infections in schools. The most important effect is to reduce the time of residence of pathogens in the classrooms.

BNT162b2 induces robust cross-variant SARS-CoV-2 immunity in children

Currently available mRNA vaccines are extremely safe and effective to prevent severe SARS-CoV-2 infections. However, the emergence of variants of concerns (VOCs) has highlighted the importance of high population-based vaccine rates to effectively suppress viral transmission and breakthrough infections. While initially left out from vaccine efforts, children have become one of the most affected age groups and are key targets to stop community and household spread. Antibodies are central for vaccine-induced protection and emerging data points to the importance of additional Fc effector functions like opsononophagocytosis or cytotoxicity, particularly in the context of VOCs that escape neutralizing antibodies. Here, we observed delayed induction and reduced magnitude of vaccine-induced antibody titers in children 5-11 years receiving two doses of the age-recommended 10 μg dose of the Pfizer SARS-CoV-2 BNT162b2 vaccine compared to adolescents (12–15 years) or adults receiving the 30 μg dose. Conversely, children mounted equivalent or more robust neutralization and opsonophagocytic functions at peak immunogenicity, pointing to a qualitatively more robust humoral functional response in children. Moreover, broad cross-VOC responses were observed across children, with enhanced IgM and parallel IgG cross-reactivity to VOCs in children compared to adults. Collectively, these data argue that despite the lower magnitude of the BNT162b2-induced antibody response in children, vaccine-induced immunity in children target VOCs broadly and exhibit enhanced functionality that may contribute to the attenuation of disease.

Infection and transmission risks of COVID-19 in schools and their contribution to population infections in Germany: A retrospective observational study using nationwide and regional health and education agency notification data

BACKGROUND

School-level infection control measures in Germany during the early Coronavirus Disease 2019 (COVID-19) pandemic differed across the 16 federal states and lacked a dependable evidence base, with available evidence limited to regional data restricted to short phases of the pandemic. This study aimed to assess the (a) infection risks in students and staff; (b) transmission risks and routes in schools; (c) effects of school-level infection control measures on school and population infection dynamics; and (d) contribution of contacts in schools to population cases.

METHODS AND FINDINGS

For this retrospective observational study, we used German federal state (NUTS-2) and county (NUTS-3) data from public health and education agencies from March 2020 to April 2022. We assessed (a) infection risk as cumulative risk and crude risk ratios and (b) secondary attack rates (SARs) with 95% confidence interval (CI). We used (c) multiple regression analysis for the effects of infection control measures such as reduced attendance, mask mandates, and vaccination coverage as absolute reduction in case incidence per 100,000 inhabitants per 14 days and in percentage relative to the population, and (d) infection dynamic modelling to determine the percentage contribution of school contacts to population cases. We included (a) nationwide NUTS-2 data from calendar weeks (W) 46-50/2020 and W08/2021-W15/2022 with 3,521,964 cases in students and 329,283 in teachers; (b) NUTS-3 data from W09-25/2021 with 85,788 student and 9,427 teacher cases; and (c) detailed data from 5 NUTS-3 regions from W09/2020 to W27/2021 with 12,814 cases (39% male, 37% female; median age 14, range 5 to 63), 43,238 contacts and 4,165 secondary cases for students (for teachers, 14,801 [22% male, 50% female; median age 39, range 16 to 75], 5,893 and 472). Infection risk (a) for students and teachers was higher than the population risk in all phases of normal presence class and highest in the early 2022 omicron wave with 30.6% (95% CI 30.5% to 32.6%) of students and 32.7% (95% CI 32.6% to 32.8%) of teachers infected in Germany. SARs (b) for students and staff were below 5% in schools throughout the study period, while SARs in households more than doubled from 13.8% (95% CI 10.6% to 17.6%) W21-39/2020 to 28.7% (95% CI 27% to 30.4%) in W08-23/2021 for students and 10.9% (95% CI 7% to 16.5%) to 32.7% (95% CI 28.2% to 37.6%) for staff. Most contacts were reported for schools, yet most secondary cases originated in households. In schools, staff predominantly infected staff. Mandatory surgical mask wearing during class in all schools was associated with a reduction in the case incidence of students and teachers (c), by 56/100,000 persons per 14 days (students: 95% CI 47.7 to 63.4; teachers: 95% CI 39.6 to 71.6; p < 0.001) and by 29.8% (95% CI 25% to 35%, p < 0.001) and 24.3% (95% CI 13% to 36%, p < 0.001) relative to the population, respectively, as were reduced attendance and higher vaccination coverage. The contribution of contacts in schools to population cases (d) was 2% to 20%, lowest during school closures/vacation and peaked during normal presence class intervals, with the overall peak early during the omicron wave. Limitations include underdetection, misclassification of contacts, interviewer/interviewee dependence of contact-tracing, and lack of individual-level confounding factors in aggregate data regression analysis.

CONCLUSION

In this study, we observed that open schools under hygiene measures and testing strategies contributed up to 20% of population infections during the omicron wave early 2022, and as little as 2% during vacations/school closures; about a third of students and teachers were infected during the omicron wave in early 2022 in Germany. Mandatory mask wearing during class in all school types and reduced attendance models were associated with a reduced infection risk in schools.

Lifting Universal Masking in Schools - Covid-19 Incidence among Students and Staff

BACKGROUND

In February 2022, Massachusetts rescinded a statewide universal masking policy in public schools, and many Massachusetts school districts lifted masking requirements during the subsequent weeks. In the greater Boston area, only two school districts - the Boston and neighboring Chelsea districts - sustained masking requirements through June 2022. The staggered lifting of masking requirements provided an opportunity to examine the effect of universal masking policies on the incidence of coronavirus disease 2019 (Covid-19) in schools.

METHODS

We used a difference-in-differences analysis for staggered policy implementation to compare the incidence of Covid-19 among students and staff in school districts in the greater Boston area that lifted masking requirements with the incidence in districts that sustained masking requirements during the 2021-2022 school year. Characteristics of the school districts were also compared.

RESULTS

Before the statewide masking policy was rescinded, trends in the incidence of Covid-19 were similar across school districts. During the 15 weeks after the statewide masking policy was rescinded, the lifting of masking requirements was associated with an additional 44.9 cases per 1000 students and staff (95% confidence interval, 32.6 to 57.1), which corresponded to an estimated 11,901 cases and to 29.4% of the cases in all districts during that time. Districts that chose to sustain masking requirements longer tended to have school buildings that were older and in worse condition and to have more students per classroom than districts that chose to lift masking requirements earlier. In addition, these districts had higher percentages of low-income students, students with disabilities, and students who were English-language learners, as well as higher percentages of Black and Latinx students and staff. Our results support universal masking as an important strategy for reducing Covid-19 incidence in schools and loss of in-person school days. As such, we believe that universal masking may be especially useful for mitigating effects of structural racism in schools, including potential deepening of educational inequities.

CONCLUSIONS

Among school districts in the greater Boston area, the lifting of masking requirements was associated with an additional 44.9 Covid-19 cases per 1000 students and staff during the 15 weeks after the statewide masking policy was rescinded.

Evaluation of different types of face masks to limit the spread of SARS-CoV-2: a modeling study

We expanded a published mathematical model of SARS-CoV-2 transmission with complex, age-structured transmission and with laboratory-derived source and wearer protection efficacy estimates for a variety of face masks to estimate their impact on COVID-19 incidence and related mortality in the United States. The model was also improved to allow realistic age-structured transmission with a pre-specified R0 of transmission, and to include more compartments and parameters, e.g. for groups such as detected and undetected asymptomatic infectious cases who mask up at different rates. When masks are used at typically-observed population rates of 80% for those ≥ 65 years and 60% for those < 65 years, face masks are associated with 69% (cloth) to 78% (medical procedure mask) reductions in cumulative COVID-19 infections and 82% (cloth) to 87% (medical procedure mask) reductions in related deaths over a 6-month timeline in the model, assuming a basic reproductive number of 2.5. If cloth or medical procedure masks’ source control and wearer protection efficacies are boosted about 30% each to 84% and 60% by cloth over medical procedure masking, fitters, or braces, the COVID-19 basic reproductive number of 2.5 could be reduced to an effective reproductive number ≤ 1.0, and from 6.0 to 2.3 for a variant of concern similar to delta (B.1.617.2). For variants of concern similar to omicron (B.1.1.529) or the sub-lineage BA.2, modeled reductions in effective reproduction number due to similar high quality, high prevalence mask wearing is more modest (to 3.9 and 5.0 from an R₀ = 10.0 and 13.0, respectively). None-the-less, the ratio of incident risk for masked vs. non-masked populations still shows a benefit of wearing masks even with the higher R0 variants.

Face masking and COVID-19: potential effects of variolation on transmission dynamics

Face masks do not completely prevent transmission of respiratory infections, but masked individuals are likely to inhale fewer infectious particles. If smaller infectious doses tend to yield milder infections, yet ultimately induce similar levels of immunity, then masking could reduce the prevalence of severe disease even if the total number of infections is unaffected. It has been suggested that this effect of masking is analogous to the pre-vaccination practice of variolation for smallpox, whereby susceptible individuals were intentionally infected with small doses of live virus (and often acquired immunity without severe disease). We present a simple epidemiological model in which mask-induced variolation causes milder infections, potentially with lower transmission rate and/or different duration. We derive relationships between the effectiveness of mask-induced variolation and important epidemiological metrics (the basic reproduction number and initial epidemic growth rate, and the peak prevalence, attack rate and equilibrium prevalence of severe infections). We illustrate our results using parameter estimates for the original SARS-CoV-2 wild-type virus, as well as the Alpha, Delta and Omicron variants. Our results suggest that if variolation is a genuine side-effect of masking, then the importance of face masks as a tool for reducing healthcare burdens from COVID-19 may be under-appreciated.