Preventing COVID-19: physical distancing, face masks and eye protection

Findings of this meta-analysis support physical distancing and the use of face masks and eye protection to help prevent virus transmission.¹

Physical distancing of at least 1 metre may reduce the risk of SARS-CoV-2 transmission but distances of 2 metres could be more effective, according to a systematic review and meta-analysis.

Published in The Lancet, the review of 172 observational studies across 16 countries also found that protective eye coverings and face masks were protective for healthcare workers and the general public.

The researchers identified 44 comparative studies of 25,697 patients with COVID-19, severe acute respiratory syndrome (SARS) or Middle East respiratory syndrome (MERS) in healthcare and nonhealthcare settings. They found that physical distancing of 1 metre or more was associated with an 82% lower risk of infection (adjusted odds ratio [aOR], 0.18) compared with a distance of less than 1 metre. Risk was lowered further with increasing distance, extrapolated up to 3 metres.

Use of face masks and respirators reduced the risk of infection by 85% (aOR, 0.15) compared with no face mask use. N95 respirators were linked with greater protection than disposable surgical face masks or similar (e.g. reusable 12- to 16-layer cotton masks), but both were protective. After adjusting for N95 respirator use in the healthcare setting, the researchers found face-mask use to be similarly effective in both the healthcare and nonhealthcare settings.

Eye protection with face shields, goggles and glasses was also found to be protective, with a 78% lower risk of infection compared with no eye protection (aOR, 0.22).

None of these interventions, even when properly used and combined, provided complete protection from infection, the researchers noted, stressing the need for other basic measures such as hand hygiene.

Chu and colleagues’ meta-analysis, supported by the WHO, included studies of observational data from both healthcare and nonhealthcare settings, including 44 comparative studies involving nearly 26,000 patients with COVID-19, SARS or MERS.¹ Their findings confirmed the importance of measures such as physical distancing, protective eye covering and facemasks in both settings. They observed that in healthcare settings N95 or similar respirators were 96% effective (aOR, 0.04; 95% CI, 0.004–0.30) compared with other masks, which were 67% effective (aOR, 0.33; 95% CI, 0.17–0.61) and noted the importance of eye protection which resulted in a 78% reduction in infection.

Discussion in this paper included the biological plausibility of aerosol spread of SARS-CoV-2, albeit with a lack of data to support viable virus in the air outside of aerosol generating procedures. The authors were unable to identify robust data to inform other aspects relevant to spread of infection, such as ventilation and healthcare setting (ED/ICU/ward-based /other), that may modify the degree of protection provided by personal protection strategies. Of note, the accompanying editorial by MacIntyre, et al. strongly supported the use of a respirator as the minimum standard of care for healthcare workers on COVID-19 wards, based on the precautionary principle.² 

Of relevance to this discussion, in the Australian setting, Victorian Chief Medical Officer Andrew Wilson reported on 25 August 2020 that 70 to 80% of healthcare workers infected with SARS-CoV-2 in Victoria’s second wave of infection were infected at work.³