# COVID-19 Incidence and Age Eligibility for Elementary School

## TL;DR

This study found that children eligible for kindergarten in California had higher rates of COVID-19 during in-person school semesters compared to those just past the age cutoff.

## Contribution

The study introduces a regression discontinuity design to assess the association between school attendance and SARS-CoV-2 transmission among children.

## Key findings

- Children eligible for kindergarten had higher COVID-19 incidence during in-person semesters compared to those born just after the age threshold.
- The association between school eligibility and infection decreased over time and was smaller than associations with out-of-school gatherings.
- No significant association was found between school eligibility and hospitalization rates.

## Abstract

Was eligibility for elementary school associated with COVID-19 infection in
California?

In this case series study, using regression discontinuity methods that adjusted for
differential testing rates in schooled populations, higher incidences of COVID-19 were
found among California children eligible for kindergarten compared with children born
just after the age threshold for school eligibility during in-person semesters: fall
2021 (51.5% higher), spring 2021 (26.3% higher), and fall 2022 (19.1% higher). No
associations were found between school eligibility and hospitalization.

This study suggests that associations between school eligibility and COVID-19 incidence
decreased over time and were generally smaller than published associations between
out-of-school gatherings and incidence.

Understanding the role of school attendance on transmission of SARS-CoV-2 among
children is of importance for responding to future epidemics. Estimating discontinuities
in outcomes by age of eligibility for school attendance has been used to examine
associations between school attendance and a variety of outcomes, but has yet to be
applied to describe associations between school attendance and communicable disease
transmission.

To estimate the association between eligibility for elementary school and COVID-19
incidence.

This case series used data on all pediatric COVID-19 cases reported to
California’s disease surveillance system between May 16, 2020, and December 15,
2022, among children within 24 months of the age threshold for school eligibility.

Birthdate before or after the age threshold for elementary school eligibility during
periods when school was remote vs in person.

COVID-19 cases and hospitalizations.

Between May 16, 2020, and December 15, 2022, there were 688 278 cases of COVID-19
(348 957 cases [50.7%] among boys) and 1423 hospitalizations among children who
turned 5 years within 24 months of September 1 of the school year when their infection
occurred. The mean (SD) age of the study sample was 5.0 (1.3) years. After adjusting for
higher rates of testing in schooled populations, the estimated pooled incidence rate
ratio among kindergarten-eligible individuals (eg, those born just before the age
threshold for school eligibility) compared with those born just after the eligibility
threshold for in-person fall 2021 semester was 1.52 (95% CI, 1.36-1.68), for in-person
spring 2022 semester was 1.26 (95% CI, 1.15-1.39), and for in-person fall 2022 semester
was 1.19 (95% CI, 1.03-1.38). Reported incidence rates among school-eligible children
remained higher during the month-long winter 2021-2022 school break but were lower
during the longer summer break that followed. The findings were unable to establish
whether associations between school eligibility and COVID-19 incidence were based on
in-school vs out-of-school routes (eg, classrooms vs school buses). The study lacked
power to detect associations between school attendance and hospitalization. Results were
robust to functional form. A simulation study was conducted to demonstrate bias
associated with nonadjustment for differential case acquisition by exposure status.

In this case series of children in California, the magnitude of the association between
school eligibility and COVID-19 incidence decreased over time and was generally lower
than other published associations between out-of-school child social interactions and
COVID-19 incidence. This regression discontinuity design approach could be adapted to
other geographies and/or disease systems to assess associations between schooling and
disease transmission.

This case series used data on pediatric COVID-19 cases reported to California’s
disease surveillance system to estimate the association between eligibility for elementary
school and COVID-19 incidence.