How school eligibility influences the spread of infectious diseases: Insights for future outbreaks

(Press-News.org) A recent study in JAMA Network Open sheds light on how school attendance influences the spread of infectious diseases, using COVID-19 as a case study. Researchers analyzed the natural age cutoff for kindergarten eligibility in California to compare COVID-19 rates between children old enough to start school and those who were not. This approach, called regression discontinuity, offers a way to rapidly understand the role of schools in disease transmission and evaluate the effectiveness of within-school prevention measures without requiring additional data collection or school closures.

The study's findings underscore the complexity of school-based transmission and highlight the effectiveness of school-based prevention measures. The findings can be applied to other infectious diseases, such as novel flu strains or respiratory viruses, enabling schools and public health officials to make informed decisions during future outbreaks. 

Jennifer Head, senior author of the study and John G. Searle Assistant Professor of Epidemiology at the University of Michigan School of Public Health, discusses the study’s broader implications for public health and future outbreak responses.

What makes this study’s approach to examining COVID-19 in schools unique? In this study, we used a method called regression discontinuity to examine the connection between school attendance and COVID-19 rates in children. This method looks at whether children born just before the age cutoff for kindergarten have different COVID-19 rates compared to those born just after.

Children born on either side of this age threshold are assumed to be similar in most ways, so differences in COVID-19 rates can be attributed, at least partly, to school attendance. While previous studies have used age thresholds for school attendance to study other outcomes like crime or adult earnings, this is the first to our knowledge to apply it to understanding the impact of schooling on an infectious disease.

A major advantage of this approach is that it lets us study the effects of school attendance on disease spread without requiring school closures. The approach allows estimation and comparison of the effects across different school districts or counties, permitting identification of district or county-level characteristics (like vaccination rates) that are associated with weaker associations between schooling and disease transmission. The approach also uses routine public health data, like birthdates and COVID-19 case reports, making it a practical way to analyze school-related disease transmission even when time and resources are limited.

What does this study reveal? After accounting for age and the fact that children attending school were tested more often than those who didn’t attend, we found that COVID-19 rates were higher among children eligible for kindergarten compared to those who were not during in-person semesters. Importantly, this difference decreased with each semester, and there was lower transmission among school eligible children compared to those not eligible during summer breaks following in-person semesters.

Specifically, COVID-19 rates were 52% higher for school-eligible children than non-eligible children in the fall 2021 semester, 26% higher in the spring 2022 semester, and 19% higher in the fall 2022 semester. When schools were closed for in-person instruction, we found no difference in COVID-19 rates between the two groups, which supports the idea that these differences are linked to school attendance rather than other factors.

We also found no link between in-person schooling and COVID-19 hospitalizations. This aligns with other studies showing that school attendance has little impact on COVID-19 hospitalizations, likely because severe cases are a relative rarity in young children.

How could this study's findings guide schools’ approaches for future infectious disease outbreaks? Anywhere people gather, there’s a higher risk of spreading infectious diseases, and schools are no exception. In our study, we saw higher COVID-19 transmission among school-eligible children compared to those not eligible for school.

That said, it’s critical to weigh this risk against the significant downsides of closing schools, such as learning loss, mental health challenges, and increased disparities in education and the workplace. When we compared the link between school eligibility and COVID-19 in this study to other settings, like social gatherings outside of school, we found that the risk in schools wasn’t any greater. Based on the strength of our association, we believe that our findings support the use of within-school cautionary measures as much as possible over school closures.

While children are less likely than adults to experience severe COVID-19 symptoms, other diseases, like influenza, can have more serious effects on kids. The method we used in this study provides a quick and effective way to evaluate how in-person schooling influences the spread of different pathogens, especially for emerging pathogens or novel strains of known pathogens. This method may also be useful to examine to what degree pediatric vaccinations reduce school-disease associations, which is especially important in the context of rising vaccine hesitancy. 

What role did vaccination and natural immunity play in the changes you observed over time? COVID-19 vaccinations for children aged 5–11 years old became available late in the fall 2021 semester, meaning children on both sides of the kindergarten age-eligibility threshold could gain vaccine-induced protection by the start of the spring 2022 semester. Over time, we saw a steady decline in the link between school eligibility and COVID-19 rates, likely due to growing immunity from both vaccination and natural infection in children.

One line of evidence to support this theory is our finding that COVID-19 rates were lower among school-eligible children than non-eligible children during the summer break of 2022. One explanation is that school-eligible children developed higher levels of natural immunity during the 2021–2022 school year, which helped protect them during the summer.

Second, we found that counties with higher vaccination rates among children and adults had weaker associations between school eligibility and COVID-19 rates. While this trend wasn’t statistically significant, it was consistent across all three in-person semesters.

Third, in comparing counties, we found that larger counties—home to California’s largest school districts, like Los Angeles and San Francisco—had weaker links between school eligibility and COVID-19 rates. These counties had higher transmission before in-person schooling began, which may have increased natural immunity among children. They also had higher vaccination rates and followed stricter mask mandates, which likely contributed to this trend.

What else does this study tell us about disease spread in schools? The link between school eligibility and COVID-19 rates likely reflects more than just what happens in the classroom. Other factors tied to schooling—like riding the bus, participating in sports or after-school programs, or having a parent return to work—may also play a role. This is important because earlier research suggests that children’s social interactions outside the classroom can lead to higher transmission rates than interactions inside the classroom.

 

Paper cited: “COVID-19 Incidence and Age Eligibility for Elementary School.” JAMA Network Open. DOI:10.1001/jamanetworkopen.2024.44836 

Additional authors of the study include: Eve Lin and Vivian Lee of the College of Letters and Sciences, University of California, Berkeley; Alyssa Bilinski of Brown University School of Public Health; Philip Collender and Justin Remais of the Division of Environmental Health Sciences, University of California, Berkeley; Sohil Sud, Tomás León, and Lauren White of the California Department of Public Health, Richmond.

Listen to Head discuss the work on the JAMA Network Open Conversations podcast  

About the University of Michigan School of Public Health Since 1941, the University of Michigan School of Public Health has been pursuing a healthier, more equitable world through education, research and action. Ranked among the top schools of public health in the country, Michigan Public Health trains more than 1,300 graduate and undergraduate students each year. With more than 190 faculty and researchers across six academic departments and numerous collaborative centers and institutes, the school produces impactful research aimed at finding lasting solutions to pressing public health challenges. Compassion, innovation and inclusion drive Michigan Public Health faculty, staff, students and more than 19,000 alumni worldwide to pursue positive change and make a lasting impact on the health of the world. Learn more at publichealth.umich.edu or follow us on social media at @umichsph.

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