This comprehensive study analyzes the impact of air purification methods on respiratory infections, especially COVID-19. It finds that contrary to popular belief, these methods do not significantly decrease the incidence of diseases. Additionally, the review casts doubt on the benefits of increased air circulation.
The study evaluates the effectiveness of air purification methods in preventing respiratory diseases such as COVID-19, highlighting a lack of substantial proof and their minimal effect on lowering infection rates.
The COVID-19 pandemic sparked widespread advocacy for better indoor air quality, believed to mitigate virus transmission. However, empirical evidence supporting these claims is insufficient, and relevant studies from the pandemic era are yet to be published.
My colleagues and I examined pre-COVID evidence and determined that air purification does not effectively reduce respiratory infection illnesses.
Air purifiers typically include filters and disinfectors. Filters remove airborne particles potentially carrying viruses, while disinfectors use UV radiation or ozone to neutralize airborne viruses.
Our comprehensive review covered 32 studies from 1970 to 2022, concluding that these technologies do not significantly impact illness frequency or severity.
Although some evidence indicated fewer infections from laboratory-confirmed influenza or norovirus, this was overshadowed by a strong publication bias – the tendency to publish positive results more frequently than negative ones.
This bias overstates the apparent effectiveness of treatments or interventions, as negative studies often remain unpublished.
The review ultimately found no compelling evidence that air purification methods reduce respiratory illness transmission risks.
None of the reviewed studies specifically focused on COVID-19, as they predated the pandemic.
A recent German study, however, assessed the impact of HEPA filters on COVID-19 in kindergartens. Comparing illness rates in schools with and without new filters, it found no significant differences, with infection rates being slightly higher in schools with filters.
While ventilation might offer some benefits in reducing infection, the evidence supporting this is weak.
The study did not include research on how increased ventilation, like open windows, affects illness risk. One issue with air treatment studies is the potential reduction in ventilation rates, which could heighten the risk.
Another recent review examined ventilation’s impact on COVID-19 infection. Although it slightly favored ventilation in reducing infection, the studies were of low quality, leading researchers to deem this conclusion as weakly supported.
Therefore, differences in ventilation likely don’t account for the negative outcomes in air treatment studies.
Factors Affecting Transmission Risk
If air treatment doesn’t lower illness risk, why might that be? Several factors suggest why air treatment technologies may not be the comprehensive solution some claimed.
Firstly, respiratory virus transmission risk is closely linked to proximity to an infected person. Early in the pandemic, research showed a significant drop in infection risk with increased distance from an infectious individual.
Close person-to-person transmission is unlikely to be affected by air treatment.
Secondly, even if air treatment could prevent infection within a specific area, people frequently move between different environments. Air treatment in schools or workplaces won’t protect individuals in public transport or other communal settings.
Lastly, the dynamics of infections with short immunity durations matter. As I previously discussed, infections like COVID, characterized by brief immunity, exhibit different patterns from standard epidemic models, with reinfections common as immunity wanes.
COVID-like infections are more accurately represented by the SEIRS model, where interventions like air filtration or masks become less effective as reinfections predominate. Infection rates are then driven by the rate of immunity loss.
In conclusion, the prevailing evidence suggests that air treatment technologies do not significantly lower the risk of respiratory infections like COVID. While there is some indication that increased ventilation might reduce this risk, the evidence is not strong.
Authored by Paul Hunter, Professor of Medicine, University of East Anglia.
Paul Hunter serves as a consultant for the World Health Organization and receives funding from the National Institute for Health Research, the World Health Organization, and the European Regional Development Fund.
Based on an article originally appearing in The Conversation.
Frequently Asked Questions (FAQs) about Air Purifier Effectiveness
Do Air Purifiers Reduce the Risk of Respiratory Infections Like COVID-19?
No strong evidence suggests that air purifiers significantly reduce the risk of respiratory infections, including COVID-19. Studies indicate that air purification technologies, including filters and disinfectors, do not notably decrease illness frequency or severity.
How Effective are HEPA Filters Against COVID-19 in Schools?
A German study focusing on HEPA filters in kindergartens found no significant difference in COVID-19 infection rates between schools with and without these filters. In some cases, schools with filters had slightly higher infection rates.
Can Improved Ventilation Help Prevent Respiratory Infections?
While there is some evidence suggesting that increased ventilation might reduce the risk of respiratory infections, the overall quality of these studies is low. Therefore, the effectiveness of ventilation as a preventive measure remains inconclusive.
What Factors Influence the Transmission of Respiratory Viruses?
The proximity to an infected person significantly affects the transmission risk of respiratory viruses. Additionally, the effectiveness of air treatment is limited due to people frequently moving between different environments and the dynamics of infections with short immunity durations.
Is There a Bias in Publishing Studies on Air Treatment and Respiratory Infections?
Yes, there is a strong publication bias in this field. Studies with positive results are more likely to be published than those with negative outcomes, leading to an overstated perception of the effectiveness of air treatment technologies.
More about Air Purifier Effectiveness
- Original Article on The Conversation
- [German Study on HEPA Filters and COVID-19 in Schools](Provide link if available)
- [Studies on Ventilation and COVID-19 Infection](Provide link if available)