A clinical trial has shown that face masks can protect against respiratory illnesses such as flu and the common cold, but convincing people to wear them is harder.
Researchers at the University of New South Wales, Australia, and the Medical Research Council Centre for Outbreak Analysis and Modelling at Imperial College London ran a clinical trial to investigate the effectiveness of masks. They found that adults who wore masks in the home were four times less likely than non-wearers to be infected by children in the household with a respiratory infection.
“In a severe influenza pandemic, there may be limited availability of vaccines in the first few months,” said Professor Neil Ferguson, Director of the MRC Centre for Outbreak Analysis and Modelling at Imperial College London and an author on the study. “In that context, masks are a potentially important additional weapon in the public health arsenal.”
The University of New South Wales team, led by Professor Raina MacIntyre, recruited more than 280 adults in 143 families in Sydney during the winter seasons of 2006 and 2007. The adults were randomly allocated masks when exposed to a sick child in the household.
Less than half of those asked to wear masks reported having done so consistently. However, adherence to preventative measures is known to vary depending on perception of risk and could be expected to increase during a respiratory disease pandemic.
The trial results are published this week in Emerging Infectious Diseases, the journal of the US Centres for Disease Control and Prevention. The researchers say the findings have global implications and are particularly relevant to efforts to combat the spread of flu pandemics and other emerging respiratory diseases such as SARS.
But while some governments are already stockpiling masks for use in a pandemic, Professor Ferguson said the evidence to support their use in the community has been limited up until now.
“This study starts to close that evidence gap. Our work indicates masks may provide substantial protection so long as they are worn consistently and properly.”
He went on to emphasise that uncertainties remain:
“This study represents a first step. More work is needed to look at the effectiveness of masks to prevent flu infections specifically, to evaluate their effectiveness in other community and healthcare settings, and to investigate the factors limiting compliance with mask use. We estimate that the reduction in risk of catching a respiratory infection for an adult caring for a sick child, when they adhere to mask use, is between sixty and eighty per cent. Whether the risk would be reduced by the same margin in another setting or where there was more than one source of potential infection requires further investigation.”
The study was funded by the Australian Department of Health and Ageing.
(Source: Australian Department of Health and Ageing: Ferguson N, et al. Effectiveness of face mask use to control respiratory virus transmission in households. Emerging Infectious Diseases: February 2009)