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  Conference on Retroviruses
and Opportunistic Infections
Seattle, Washington
Feb 19-22 2023
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Every 10% Uptick in Masking at School Halves SARS-CoV-2 Detections
  30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle
Mark Mascolini
Every 10% rise in full masking by elementary school students, staff, and parents halved SARS-CoV-2 shedding detected in school wastewater, according to a direct observation of 10 schools in the San Diego area over 3 months in 2022 [1]. Only about one third of children and adults observed were fully masked, and that rate may be closer to 0 today.
Studies confirming the efficacy of masking in preventing SARS-CoV-2 transmission are legion, and the American Academy of Pediatrics recommends masking as one facet of a COVID prevention policy. But most states and school districts dropped masking mandates a long time ago. So why study the impact of masking in schools today?
University of California, San Diego (UCSD) researchers who conducted this study have an answer: During the school year, children spend most of their waking hours in school. SARS-CoV-2 vaccination rates remain low in kids. And children take home whatever bug they pick up in school. The UCSD team also noted that previous studies of school masking often lack power because they rely on self-reports of masking, they accept stated policies as a proxy for actual masking behavior, and access to testing biases surveillance data.
UCSD investigators sought to improve the school-masking test model by sampling school wastewater for SARS-CoV-2 (which their prior research found can identify 95% of PCR-detectable COVID-19 cases in school) and by directly observing masking rates by putting head (and mask) counters outside school doors when sessions ended for the day.
From March 2 to May 27, 2022 (when the Omicron variant dominated in the area), the researchers randomly picked 10 schools in a project working with historically marginalized San Diego communities. They sent 2 trained observers to each school twice a week to count students, staff, and parents leaving school after the final bell and recording how many were fully masked (mask covering nose and mouth), partially masked (something other than full masking), and no masking. They sampled school wastewater in the 5 days after each observation and built a logistic regression model to gauge the association between a positive wastewater signal and percentage of fully masked people (versus partially masked or unmasked), adjusting for intrasite correlation, observation week, and current case rate and SARS-CoV-2 vaccination rate in the school ZIP code.
By the end of the study period, the observers had counted school children and adults 60 times. These observers figured an average 40% of children wore masks, compared with 27% of adults, for an overall masking rate of 36%. They got a positive wastewater signal (meaning SARS-CoV-2 could be detected in school sewage) after 9 of 60 school observations. Adjusted logistic regression analysis determined that the odds of a positive wastewater sample fell by half for every 10% increase in fully masked individuals (adjusted odds ratio 0.49, 95% confidence interval 0.27 to 0.90).
Put simply, even a small surge in the proportion of people correctly wearing a mask in a given school could put a huge dent in chances that SARS-CoV-2 circulates in that school. In a school with 350 students, behavioral interventions that encourage only 35 children to mask up could have a sizeable impact on COVID prevention.
1. Fielding-Miller R, Hassani A, Flores M, et al. Association between observed masking and SARS-CoV-2 presence in school wastewater. 30th CROI, Conference on Retroviruses and Opportunistic Infections, February 19-22, 2023, Seattle. Abstract 210.