Wearing facemasks at mass outdoor events ‘could prevent superspreading’

PEOPLE should be asked to wear face coverings when attending large outdoor gatherings such as sporting events to prevent Covid superspreading, researchers have argued.

Writing as part of a debate in the BMJ today, clinicians from California and Switzerland say the policy makes sense in settings where it is “difficult to maintain physical distance for prolonged periods”.

Although they acknowledge that the estimated risk of transmission is “four to 20 times more likely” indoors than outdoors, they say facemasks make sense outdoors when people are mixing with several other household groups.

The authors – Babak Javid of the Division of Experimental Medicine at the University of California (Ucal) and Dirk Bassler and Manuel B Bryant of University Hospital Zurich – note that the outcomes of mass outdoor events have varied.

They write: “Summer 2020 witnessed worldwide mass protests in support of the Black Lives Matter movement. At the time, many experts and pundits warned that such protests may fuel large transmission clusters for Covid-19, but these fears were not realised. By contrast, the mass outdoor Sturgis Motorcycle Rally in South Dakota, USA, is considered to have been the trigger for a huge superspreadingtype event that resulted in a devastating chain of Covid-19 transmission and disease.

“One proposed reason for the observed differences is that the Sturgis Rally was associated with lower compliance with non-pharmaceutical interventions (NPIS), such as mask-wearing and physical distancing.”

The motorcycle rally, which brought together 462,000 biker enthusiasts in August, was subsequently linked to 260,000 coronavirus cases between August 2 and September 2 by researchers at San Diego State University.

However, Dr Muge Cevik, an expert in infectious diseases and virology at St Andrews University, argues that the Sturgis Rally had “sustained and multi-day indoor components”, with epidemiological investigations finding links to restaurants and workplaces.

Dr Cevik, who advises Scotland’s Chief Medical Officer on Covid-19, said that fewer than 10 per cent of known Covid cases involved outdoor transmission. She added: “Given the low risk of transmission outdoors, recommendations or mandates for outdoor masking may seem arbitrary, affecting people’s trust and sustained energy to engage in higher yield interventions, such as indoor mask use or staying home if sick.

“Blanket outdoor mask recommendations may also confuse the public about the true nature of the relative risk and could distract from indoor settings with a much greater transmission risk.”

There is no requirement to wear masks outdoors in Scotland, and there is also growing evidence that vaccinations are curbing transmission.