Respiratory protection for healthcare workers and SARS-CoV-2: evidence is equivocal but does that matter?

So, a double blog day today! I couldn’t resist reading the latest statement from a UKHSA expert group on “The role of respirators and surgical masks in mitigating the transmission of SARS-CoV-2 in healthcare settings: an overview of evidence (2022)”, published yesterday, as soon as it hit my desk. “Equivocal” is a word that I try to avoid. It’s one of those ‘jargony’ and overly technical words that is best worded-around in my view. But for this, it’s about right. The evidence from well controlled clinical trials that respirators (FFP2/3 or N95s) offer superior protection to healthcare workers than surgical masks is equivocal (“open to more than one interpretation”). But does that matter? If we look to the physics of SARS-CoV-2 transmission, there is a risk that the type of small, virus-laden particles emitted by patients infected with SARS-CoV-2 could circumvent the level of protection provided by surgical masks. And so, it now seems reasonable to recommend FFP2/3 or N95s for healthcare workers caring for patients with SARS-CoV-2 (and influenza for that matter). However, given the uncertainty of the evidence base, as highlighted by this review, I can understand why some have decided to continue with a policy of surgical masks when caring for patients with SARS-CoV-2 infection in most settings.

Here are some things we now know for sure:

  • Respirators (I’m going to use this term as a catch-all to cover FFP2/3 and N95s) provide a higher level of filtration than surgical masks (this HSE report found a 6-fold reduction from surgical masks, and a 100-fold reduction from a fitted respirator).   
  • Patients infected with SARS-CoV-2 emit virus-laden respiratory particles in a range of sizes, including both those that would traditionally have been described as “droplet” and “aerosols”.
  • Some medical procedures (group together as “aerosol generating procedures”) can increase the risk of producing small respiratory particles, although the evidence for this is itself equivocal!
  • Transmission of SARS-CoV-2 is more likely at close range (2m or closer), but can occur over longer ranges, especially in poorly ventilated indoor spaces.
  • Masks (both surgical masks and respirators) reduce the risk of exposure to SARS-CoV-2 and other respiratory viruses.
  • Healthcare workers have had an increased risk of SARS-CoV-2 infection compared with the general public, and healthcare workers in close proximity to patients with COVID-19 have had an increased risk of SARS-CoV-2 infection amongst healthcare workers.

It’s notable that this UKHSA review of the evidence focusses only on SARS-CoV-2. Whilst there are differences in the transmission dynamics of SARS-CoV-2 and other viruses, it seems a shame not to include quite a few well-designed trails on influenza transmission (which are, of course, also equivocal)!

To illustrate the “equivocal” nature of the evidence, I’m going to quote verbatim from the conclusion of this UKHSA review:

“Evidence from one review with meta-analysis of 12 studies (mostly at high risk of bias) found no statistical differences between respirators and surgical masks. Another review with network meta-analysis found that respirators were more effective than surgical masks in reducing SARS-CoV-2 infections in healthcare workers, but this was based on a smaller number of studies (2 studies with direct comparison, number of indirect comparisons not reported; low or very low certainty).”

So, which is it? Are respirators more effective than surgical masks or not?

Overall, I commend UKSHA for putting out this detailed and thorough report, which I enjoyed reading and suggest you read in full. I really do think that the evidence (from an epidemiological viewpoint at least) is equivocal. However, despite that, I think it’s now reasonable to go down the route of respirators for staff caring for patients with SARS-CoV-2. All this being said, though, and from my own observations and experience, poor mask etiquette (whether it’s a surgical mask or a respirator) is almost certainly the biggest risk of exposure to SARS-CoV-2. A mask worn on the chin, forehead, or earlobe isn’t going to do much in reducing the risk of respiratory exposure to SARS-CoV-2!


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