Classroom Air Purifiers for Reducing School Absence

NCT ID: NCT07119333

Last Updated: 2025-11-18

Basic Information

• Recruitment Status: ENROLLING_BY_INVITATION
• Clinical Phase: NA
• Total Enrollment: 72 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2026-01-31
• Study Completion Date: 2027-03-31

Brief Summary

Background

Respiratory infections like influenza and SARS-CoV-2 pose significant global health risks due to their high transmissibility and severity. SARS-CoV-2 has caused over 7 million deaths worldwide, and the Lancet Commission estimates a >20% chance of a similar respiratory virus pandemic within a decade. Schools, often poorly ventilated, are high-risk settings for transmission. While COVID-19 school closures may have reduced transmission, they likely caused learning loss, mental health issues, and increased burdens on parents and caregivers. Air purifiers with HEPA filters may offer a non-disruptive mitigation strategy, but the evidence to support their effectiveness in reducing viral transmission is weak. This protocol describes a cluster-randomised, parallel, two-arm, group sequential superiority trial with an interim analysis-to allow early stopping for efficacy or futility-to estimate the effect of portable air purifiers with HEPA filters in primary school classrooms on student absenteeism.

Research Questions

The primary question is whether installing and operating air purifiers with HEPA-filters (intervention) reduce student absenteeism (primary outcome) compared to sham air purifiers (control). Secondary questions examine whether the intervention reduces teacher absenteeism due to respiratory infections, rate and 12-week risk of self-reported respiratory infections among teachers, and teachers' perceived air quality compared to sham air purifiers. If the trial estimates a statistically significant effect for the primary outcome, a cost-consequence analysis will evaluate the direct and indirect costs associating with operating air purifiers against the potential benefits of reduced student and teacher absenteeism. A process evaluation will explore mechanisms of effect.

Methods and Analysis

This group sequential trial will randomize schools (clusters) 1:1 to intervention or control arms in two stages: winter 2025/2026 (N = 32 schools; ~736 students) and winter 2026/2027 (N = 30 schools; ~690 students). Eligible schools must have classrooms suitable for portable air purifiers, >10 students in grades 5-7 (typically aged 10-13 years), and principal consent. Intervention and control classrooms will each receive two portable air purifiers with HEPA-filters operating at a performance equivalent to 3.0 and 0.3 air changes per hour, respectively, with control purifiers acting as shams.

Outcomes will be measured during and at the end of a 12-week period. The primary outcome is student absenteeism, measured as full child-days of absence aggregated at the class level. An interim analysis is planned at the end of the first stage, with error-spending O'Brien-Fleming stopping boundaries that are binding for efficacy and nonbinding for futility.

The primary estimand is the marginal incidence rate ratio of student absences, estimated using generalized estimating equations with a negative binomial model to account for overdispersion. Prespecified stopping boundaries will determine stopping, with efficacy boundaries being binding. Treatment effects will be estimated using cluster-bootstrapped confidence intervals adjusted to provide strong control on overall type I and II error probabilities, and a bias correction will be applied if the trial is stopped early for efficacy. All analyses will follow the intention-to-treat principle.

Ethics and Dissemination

The trial has been approved by the Regional Committees for Medical and Health Research Ethics and the National Research Ethics Committee. Results will be disseminated to stakeholders, participants and the public through peer-reviewed journals, scientific meetings and social media.

Conditions

Asenteeism

Study Design

• Allocation Method: RANDOMIZED
• Intervention Model: SEQUENTIAL
• Primary Study Purpose: PREVENTION
• Blinding Strategy: TRIPLE

Study Groups

Intervention

The intervention is the installation and operation of two portable air purifiers with HEPA filters per intervention school classroom. Each air purifier will operate at a level corresponding to 3.0 air changes per hour, providing a combined capacity corresponding to a Clean Air Delivery Rate (CADR) of at least 486 m3/hour.

Group Type: EXPERIMENTAL

Air purifiers

Intervention Type: DEVICE

Air purifiers

Control

The control is the installation and operation of two sham air purifiers per control classroom. These will be identical in appearance and placement to the intervention units and will also include a HEPA filter, but they will be modified by the manufacturer to operate at the lowest fan setting permitted by the motor. This setting results in minimal airflow and negligible air-cleaning capacity but may also produce less sound than the intervention units. The sham air purifiers will operate at a performance equivalent to 0.3 air changes per hour, providing a combined CARD of at least 48 m3/hour.

Group Type: SHAM_COMPARATOR

Sham air purifiers

Intervention Type: DEVICE

Sham air purifiers

Interventions

Air purifiers

Air purifiers

Intervention Type: DEVICE

Sham air purifiers

Sham air purifiers

Intervention Type: DEVICE

Eligibility Criteria

Inclusion Criteria

1. Schools with more than 10 students in either 5th, 6th, or 7th grade (typically aged 10-13 years).

2. Schools with at least one classroom of sufficient dimensions to accommodate the installation of two portable air purifiers.

For logistical and administrative reasons, the investigators will try to limit the sampling frame to schools in municipalities located close our offices in Oslo. These municipalities include several large towns with populations of around 30 000 to 100 000 people, as well as sparsely populated rural areas, and are therefore reasonably representative of Norway and many other countries. The investigators will enlarge the sampling frame as necessary.

The second population is teachers at primary schools in Norway. Teachers meeting the following criteria will be eligible.

1. Be the main class teacher of one or more of the classrooms included in the trial.

2. Provide informed consent.

• Minimum Eligible Age: 10 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: Yes

Sponsors

Norwegian Institute of Public Health

OTHER_GOV

Sponsor Role: lead

Responsible Party

Responsibility Role: SPONSOR

Locations

Norwegian Institute of Public Health

Oslo, Oslo County, Norway

Countries

Norway

Other Identifiers

737650

Identifier Type: -

Identifier Source: org_study_id