When a Texan farm worker caught bird flu from cattle recently, social media was abuzz with rumours. While bird flu is not a human pandemic, scientists and policymakers the world over are keen to prepare as best they can for when such a pandemic emerges – a tricky task, given that science is messy, policy must be pragmatic and people’s values don’t always align.
It’s time for masks to enter the chat. At the beginning of a pandemic caused by a novel or newly mutated virus, there may be no vaccine, no firm knowledge about how bad things will get and no specific treatment. Slowing transmission until more is known will be critical.
Getting most people to wear a mask could nip the outbreak in the bud, preventing a pandemic or lessening its impact. Wearing a mask is inconvenient, but not as inconvenient as lockdowns.
But do masks work? A review of masks and respirators, that looked only at clinical trials, concluded that there was not enough evidence to assess whether mask wearing reduces the risk of spreading or contracting respiratory diseases. However, we disagree with that.
The review, by the not-for-profit Cochrane Collaboration, failed to influence recent guidance issued by the US Centers for Disease Control and Prevention (CDC) in response to the troubling news of bird flu transmission to humans. The CDC recommended well-fitting respirators – along with overalls and safety goggles – for anyone working with potentially infected cattle until the bird flu threat subsides.
Is this latest guidance based on sound evidence? According to our new review of the evidence, yes. Like the Cochrane team, we pooled data from randomised controlled trials (RCTs) and analysed the combined data – a so-called meta-analysis.
Unlike them, we also examined non-RCT evidence, including dozens of laboratory studies which showed that respiratory infections, including the common cold, COVID, flu, measles and TB, spread mainly through the air.
Laboratory evidence showed that different mask materials are better or worse at filtering tiny particles, and more or less breathable – especially when damp. This explains why a cloth or paper mask that’s become soggy from the moisture in exhaled air gets harder to breathe through and may be less protective.
Whereas medical masks are typically tied loosely around the face (hence air can bypass the filter), respirators fit snugly and if worn at work must be fit-tested to make sure that all air inhaled or exhaled passes through a high-grade filter.