Air filtration technologies ineffective at stopping spread of infections

Air filtration technologies designed to make social or work interactions safer in indoor spaces are not effective, research has suggested.

Research funded by the National Institute for Health and Care Research (NIHR) looked at the effectiveness of air filtration technologies, germicidal lights, and ionisers in reducing the risk of catching airborne respiratory or gastrointestinal infections. Such technologies have soared in popularity since the Covid-19 pandemic.

However, the NIHR’s Health Protection Research Unit in Emergency Preparedness and Response found these technologies do not stop the spread of infections in buildings.

Professor Paul Hunter, professor in medicine at the University of East Anglia’s Norwich Medical School, said: “Air cleaners are designed to filter pollutants or contaminants out of the air that passes through them.

“When the Covid pandemic hit, many large companies and governments – including the NHS, the British military, and New York City and regional German governments – investigated installing this type of technology in a bid to reduce airborne virus particles in buildings and small spaces.

“But air treatment technologies can be expensive. So it’s reasonable to weigh up the benefits against costs, and to understand the current capabilities of such technologies.”

The researchers analysed evidence about microbial infections or symptoms in people who had been exposed – or not – to air treatment technologies.

All of the 32 studies analysed were conducted in real-world settings, such as schools or care homes. The researchers did not include any studies carried out during Covid because so far none of these has been published.

Lead researcher Dr Julii Brainard, also from UEA’s Norwich Medical School, said: “In short, we found no strong evidence that air treatment technologies are likely to protect people in real-world settings.

“There is a lot of existing evidence that environmental and surface contamination can be reduced by several air treatment strategies, especially germicidal lights and high efficiency particulate air filtration (HEPA). But the combined evidence was that these technologies don’t stop or reduce illness.

“There was some weak evidence that the air treatment methods reduced likelihood of infection, but this evidence seems biased and imbalanced. We strongly suspect that there were some relevant studies with very minor or no effect but these were never published.

“Our findings are disappointing – but it is vital that public health decision makers have a full picture. Hopefully those studies that have been done during Covid will be published soon and we can make a more informed judgement about what the value of air treatment may have been during the pandemic,” concluded Dr Brainard.