New research adds to the growing body of evidence that wearing a mask can play a significant role in reducing the spread of Covid-19.
The study from Simon Fraser University (SFU) in Canada, have found that mask mandates are associated with a 25 per cent or larger weekly reduction in Covid-19 cases.
The research also found that relaxed restrictions on businesses and gatherings (including retail, restaurants and bars) were positively associated with subsequent Covid-19 case growth - a factor that could offset and obscure the health benefits of mask mandates.
The most stringent restrictions on businesses and gatherings observed in the data were associated with a weekly decrease of 48 to 57 per cent in new cases, relative to the trend in the absence of restrictions.
For the findings, the research team analysed the impact of mask mandates that were implemented across Ontario's 34 Public Health Units (PHUs) over the course of two months.
The research team compared the results of PHUs that adopted mask mandates earlier to those that adopted mandates later.
They determined that in the first few weeks after their introduction, mask mandates were associated with an average weekly reduction of 25 to 31 per cent in newly diagnosed Covid-19 cases, relative to the trend in mask mandate absence, in July and August.
Further Canada-wide analysis with province-level data found a significantly negative association between mask mandates and subsequent COVID-19 case growth - up to a 46 per cent average reduction in weekly cases in the first several weeks after adoption.
"These results were supported by additional survey data that showed mask mandates increase self-reported mask usage in Canada by 30 percentage points, suggesting that the policy has a significant impact on behaviour," the study authors wrote.
Jointly, these results suggest that mandating indoor mask wear in public places is a powerful policy measure to slow the spread of Covid-19, with little associated economic disruption in the short term.
The study authors noted that while the results are significant, their sample period does not allow them to definitively say whether the effect of mask mandates persists or weakens beyond the first few weeks after implementation. However, they concluded that, combined with other policy measures, mask mandates can be a potent policy tool for slowing the spread of Covid-19.