Impacts of testing and immunity acquired through vaccination and infection on covid-19 cases in Massachusetts elementary and secondary students

Abstract

Background

During the 2021–22 academic year, Massachusetts supported several in-school testing programs to facilitate in-person learning. Additionally, COVID-19 vaccines became available to all school-aged children and many were infected with SARS-CoV-2. There are limited studies evaluating the impacts of these testing programs on SARS-CoV-2 cases in elementary and secondary school settings. The aim of this state-wide, retrospective cohort study was to assess the impact of testing programs and immunity on SARS-CoV-2 case rates in elementary and secondary students.

Methods

Community-level vaccination and cumulative incidence rates were combined with data about participation in and results of in-school testing programs (test-to-stay, pooled surveillance testing). School-level impacts of surveillance testing programs on SARS-CoV-2 cases in students were estimated using generalized estimating equations within a target trial emulation approach stratified by school type (elementary/middle/high). Impacts of immunity and vaccination were estimated using random effects linear regression.

Results

Here we show that among N = 652,353 students at 2141 schools participating in in-school testing programs, surveillance testing is associated with a small but measurable decrease in in-school positivity rates. During delta, pooled testing positivity rates are higher in communities with higher cumulative incidence of infection. During omicron, when immunity from prior infection became more prevalent, the effect reversed, such that communities with lower burden of infection during the earlier phases of the pandemic had higher infection rates.

Conclusions

Testing programs are an effective strategy for supporting in-person learning. Fluctuating levels of immunity acquired via natural infection or vaccination are a major determinant of SARS-CoV-2 cases in schools.

Plain language summary

During the height of the Covid-19 pandemic, multiple strategies were used to enable students to participate in in-person elementary and secondary schools. Little is known about the overall impact of prior immunity and in-person testing programs on the ability to maintain protection from Covid-19 in schools. This study, conducted in Massachusetts during the 2021-2022 academic year, found that community immunity gained through prior infection or vaccination, combined with testing strategies including testing programs to monitor infection and test to-stay modified quarantine programs, were safe and effective for allowing in-person learning. These data can be used to shape policy about in-school practices during future respiratory virus pandemics.