AsenteeismNCT07119333
Classroom Air Purifiers for Reducing School Absence
A study testing Air purifiers in people with Asenteeism, run by Norwegian Institute of Public Health at 1 site in Norway.
Trial 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. Read more about this study
- Who is it for?
- Ages 10 years and olderHealthy volunteers can take part
- Conditions the study is for
- Asenteeism
- What is being tested?
- Air purifiers
- Type of treatment
- Medical device
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 72 participants
- Where
- 1 siteNorway
- Study dates
- Jan 2026to Mar 2027
- Phase
- Interventional
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 10 years and older
- All sexes
- Healthy volunteers accepted
- Child, Adult, Older adult
There are two general trial populations. The first population is primary school children in Norway. Primary school children in primary schools meeting the following criteria will be eligible:
- Schools with more than 10 students in either 5th, 6th, or 7th grade (typically aged 10-13 years).
- Schools with at least one classroom of sufficient dimensions to accommodate the installation of two portable air purifiers.
- The school principal accepts the installation of air purifiers in at least one classroom in the 5th, 6th, or 7th grade that meets the first two inclusion criteria.
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.
- Be the main class teacher of one or more of the classrooms included in the trial.
- Provide informed consent.
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
About this study
Official title: Classroom Air Purifiers for Reducing School Absence: Protocol for a Cluster-randomized, Parallel, Two-arm, Group Sequential Superiority Trial
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.
Read more
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
- Being tested
- Air purifiers, Sham air purifiers
- Keywords
- Randomized trial, Air purifiers, Student absenteeism, respiratory infections
- Medical subject headings
- Respiratory Tract Infections
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Air purifiersDevice
Air purifiers
Sham air purifiersDevice
Sham air purifiers
| Study group | Role | What they receive |
|---|---|---|
| Intervention | Experimental | 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. Receives: Device: Air purifiers |
| Control | Sham comparator | 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. Receives: Device: Sham air purifiers |
What is being measured
The primary outcome is the main question the study is designed to answer.
Student absenteeism
The primary outcome is the number of student-days of absence per classroom, measured each week. The investigators will define a student day of absence as a day for which a student is absent for the entire day. The investigators will not distinguish between the specific students who are absent (i.e., two days of absence will be counted for one student who is absent on two days, and for two students absent for one day each).
Measured: From enrollment to the end of intervention at 12 weeks
Secondary outcomes (5)
Self-reported absence due to respiratory infections among teachers
The investigators will measure the number of teacher-days of work absence (sick leave) due to self-reported respiratory infection each week. The investigators will ask teachers "Did you experience symptoms of a cold, COVID-19 or the flu last week?". Teachers who answer "Yes" to this question, will be asked to specify the symptoms they experienced (sneezing, nasal obstruction, nasal discharge, sore throath, cough, headache, fever or general discomfort) and rate each symptom from 0 to 3, where 0 = absent, 1 = mild, 2 = moderate, 3 = severe, in accordance with the Jackson index. They will then report the number of days they experienced these symptoms (ranging from 1 to 7 days), before answering "How many days were you absent from work last week due to respiratory infection?"; their response to this question will be used to measure number of days of absence. A count of zero days will be assigned to teachers answering "No" to the first question.
Measured: From enrollment to the end of intervention at 12 weeks
Incidence of self-reported respiratory symptoms consistent with respiratory infections among teachers
The investigators will assess incidents of respiratory symptoms consistent with respiratory infections among teachers using self-reported data collected weekly. The investigators define an incident as a period during which a teacher reports symptoms for at least two consecutive calendar days, preceded and followed by at least 7 symptom-free calendar days. The investigators define symptoms of respiratory infection as meeting all four of the following criteria:
- Answering "yes" to the question "Did you experience symptoms of a cold, COVID-19 or the flu last week?".
- Reporting at least one of the following symptoms: nasal obstruction (plugged or congested), nasal discharge (runny nose), sneezing or sore throat, in the last week;
- Scoring at least four points on the Jackson scale (as assessed for the preceding week);
- Reporting that they have experienced at least one of the reported symptoms for at least two consecutive days in the last week.
Measured: From enrollment to the end of the intervention at 12 weeks
Teachers reporting respiratory infections
The investigators will assess respiratory infection as a dichotomous outcome for each teacher, based on whether they meet the case definition at any point during the 12-week follow-up.
Measured: From enrollment to the end of the intervention at 12 weeks
Teacher perceptions of air quality in classrooms
The investigators will assess teachers' perceptions of classroom air quality at the end of follow-up using the MM040 questionnaire: teachers will report whether they have experienced drafts, high room temperature, low room temperature, fluctuating room temperature, stuffy or "bad" air, dry air, unpleasant odours, noise, or dust in the air during follow-up. The response options will be: "Yes, often (every week)," "Yes, occasionally," or "No, never".
Measured: From enrollment to the end of the intervention at 12 weeks
Adverse events
The investigators define an adverse event as any significant disruption to lessons, or any accident or injury, that is attributable to the intervention or control. The investigators will instruct school principals and teachers to report such events.
Measured: From enrollment to the end of the intervention at 12 weeks
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted13 Aug 2025
- Study startJan 2026 (estimated)
- Primary completionMar 2027 (estimated)
- Study completionMar 2027 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (1)Papers the sponsor has linked to this study.
- Other trials for AsenteeismStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Sequential
- Model description
- 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. 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
- Masking
- Triple blind
- Who is masked
- Participant, Investigator, Outcomes assessor
- Enrolment
- 72 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Norwegian Institute of Public Health
- Sponsor type
- Other government
- Responsible party
- Sponsor
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07119333
- Sponsor's protocol ID
- 737650
- Status last verified
- Aug 2025
- First submitted
- 11 Aug 2025
- Last updated
- 18 Nov 2025
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: The final anonymised dataset and statistical code will be archived and made freely available to the public on GitHub and will be assigned a digital object identifier in the main article.
Publications
Solberg RB, Holos SB, Elgersma IH, Elstrom P, Rose CJ, Helleve A, Gopinathan U, Fretheim A. Classroom air purifiers for reducing school absence: study protocol for a pragmatic, cluster-randomised, parallel, two-arm, group sequential superiority trial. BMJ Open. 2025 Dec 24;15(12):e109659. doi: 10.1136/bmjopen-2025-109659.
PubMed 41448709
Study at a glance
From the registry record, last updated by the sponsor on 18 Nov 2025. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Classroom Air Purifiers for Reducing School Absence: Protocol for a Cluster-randomized, Parallel, Two-arm, Group Sequential Superiority Trial
- ClinicalTrials.gov ID
- NCT07119333
- Acronym / sponsor ID
- 737650
- Conditions
- Asenteeism
- Keywords
- Randomized trial, Air purifiers, Student absenteeism, respiratory infections
- Study type
- Interventional
- Recruitment status
- Enrolling by invitation
- Enrolment
- 72 participants (estimated)
- Lead sponsor
- Norwegian Institute of Public HealthOther government
- Study start
- Jan 2026 (estimated)
- Primary completion
- Mar 2027 (estimated)
- Study completion
- Mar 2027 (estimated)
- First posted
- 13 Aug 2025 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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.
Study design
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Sequential
- Masking
- Triple blind (participant, investigator, outcomes assessor)
- Number of arms
- 2
- Model description
- 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. 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
| Arm | Type | Receives |
|---|---|---|
| Intervention | Experimental | Device: Air purifiersThe 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. |
| Control | Sham comparator | Device: Sham air purifiersThe 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. |
Who may qualify
- Ages
- 10 years and older
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Child, Adult, Older adult
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Air purifiersAir purifiers | Device | Intervention |
| Sham air purifiersSham air purifiers | Device | Control |
Primary outcome
Student absenteeism
Time frame: From enrollment to the end of intervention at 12 weeks
The primary outcome is the number of student-days of absence per classroom, measured each week. The investigators will define a student day of absence as a day for which a student is absent for the entire day. The investigators will not distinguish between the specific students who are absent (i.e., two days of absence will be counted for one student who is absent on two days, and for two students absent for one day each).
5 secondary outcomes
Self-reported absence due to respiratory infections among teachers
Time frame: From enrollment to the end of intervention at 12 weeks
Incidence of self-reported respiratory symptoms consistent with respiratory infections among teachers
Time frame: From enrollment to the end of the intervention at 12 weeks
Teachers reporting respiratory infections
Time frame: From enrollment to the end of the intervention at 12 weeks
Teacher perceptions of air quality in classrooms
Time frame: From enrollment to the end of the intervention at 12 weeks
Adverse events
Time frame: From enrollment to the end of the intervention at 12 weeks
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 18 Nov 2025.
- Derived from this study: PubMed 41448709Solberg RB, Holos SB, Elgersma IH, Elstrom P, Rose CJ, Helleve A, Gopinathan U, Fretheim A. Classroom air purifiers for reducing school absence: study protocol for a pragmatic, cluster-randomised, parallel, two-arm, group sequential superiority trial. BMJ Open. 2025 Dec 24;15(12):e109659. doi: 10.1136/bmjopen-2025-109659.
- Individual participant dataSharing planned: Yes. The final anonymised dataset and statistical code will be archived and made freely available to the public on GitHub and will be assigned a digital object identifier in the main article.
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
The record lists no contact. Use the official record to reach the sponsor.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Air purifiers in people with Asenteeism, run by Norwegian Institute of Public Health at 1 site in Norway.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: enrolling by invitation, as of the sponsor's last update on 18 Nov 2025. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Norway. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Student absenteeism (time frame: From enrollment to the end of intervention at 12 weeks). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT07119333, which also lists 1 linked publication.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 18 Nov 2025.