Mask mandates shown to significantly reduce spread of COVID-19

A new study by Simon Fraser University (SFU) researchers has found clear evidence that wearing a mask can have a significant impact on the spread of COVID-19. The researchers, from SFU's Department of Economics, have determined that mask mandates are associated with a 25 per cent or larger weekly reduction in COVID-19 cases.

The finding of their study, still in preprint and not yet peer-reviewed, conclude that mandating indoor masks nationwide in early July could have reduced the weekly number of new cases in Canada by 25 to 40 per cent in mid-August, which translates into 700 to 1,100 fewer cases per week.

The study analysed the impact of mask mandates that were implemented across Ontario's 34 Public Health Units (PHUs) over the course of two months.

Researchers 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.

A 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 percent 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.

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 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.

The study authors note 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 conclude that, combined with other policy measures, mask mandates can be a potent policy tool for slowing the spread of COVID-19.

Key Finding:

  • Mask mandates are associated with a 25 to 46 per cent average reduction in weekly COVID-19 cases across Canada.
  • Requiring indoor masks nationwide in early July could have reduced new COVID-19 cases in Canada by 25 to 40 per cent in mid-August, which translates into 700 to 1,100 fewer cases per week.
  • Mask mandates were shown to increase self-reported mask usage in Canada by 30 percentage points.
  • The most stringent restrictions on businesses and gatherings (including retail, restaurants and bars) were associated with a weekly decrease of 48 to 57 per cent in new cases, relative to the trend in the absence of restrictions.

Alexander Karaivanov, Shih En Lu, Hitoshi Shigeoka, Cong Chen, Stephanie Pamplona.
Face Masks, Public Policies and Slowing the Spread of COVID-19: Evidence from Canada.
medRxiv, 2020. doi: 10.1101/2020.09.24.20201178

Most Popular Now

Sanofi and GSK sign agreements with the Government…

Sanofi and GSK have signed agreements with the Government of Canada for the supply of up to 72 million doses of an adjuvanted COVID-19 vaccine, beginning in 2021. Thom...

BioNTech and Pfizer initiate rolling submission to…

Pfizer Inc. (NYSE: PFE) and BioNTech SE (Nasdaq: BNTX) today announced the initiation of a rolling submission to the European Medicines Agency (EMA) for BNT162b2, the lea...

Johnson & Johnson initiates pivotal global Pha…

Johnson & Johnson (NYSE: JNJ) (the Company) announced the launch of its large-scale, pivotal, multi-country Phase 3 trial (ENSEMBLE) for its COVID-19 vaccine candidate, J...

Scientists trace severe COVID-19 to faulty genes a…

More than 10 percent of young and healthy people who develop severe COVID-19 have misguided antibodies that attack not the virus, but the immune system itself, new resear...

Vir Biotechnology and GSK announce global expansio…

Vir Biotechnology, Inc. (Nasdaq: VIR) and GlaxoSmithKline plc (LSE/NYSE: GSK) announced the global expansion to Phase 3 of the COMET-ICE (COVID-19 Monoclonal antibody Eff...

Johnson & Johnson announces European Commissio…

Johnson & Johnson (NYSE: JNJ) (the Company) announced the European Commission (EC), acting on behalf of the European Union (EU) Member States, has approved an Advance Pur...

Johns Hopkins researchers publish COVID-19 'predic…

Using a combination of demographic and clinical data gathered from seven weeks of COVID-19 patient care early in the coronavirus pandemic, Johns Hopkins researchers today...

Web resources bring new insight into COVID-19

Researchers around the world are a step closer to a better understanding of the intricacies of COVID-19 thanks to two new web resources developed by investigators at Bayl...

COVID-19 vaccine AZD1222 clinical trial resumed in…

The Phase I/II clinical trial for the COVID-19 vaccine AZD1222 has resumed in Japan after discussion with the Japanese Pharmaceuticals and Medical Devices Agency (PMDA). ...

COVID-19 Long-Acting AntiBody (LAAB) combination A…

AstraZeneca's long-acting antibody (LAAB) combination, AZD7442, will advance into two Phase III clinical trials in more than 6,000 participants at sites in and outside th...

Adequate levels of vitamin D reduces complications…

Hospitalized COVID-19 patients who were vitamin D sufficient, with a blood level of 25-hydroxyvitamin D of at least 30 ng/mL (a measure of vitamin D status), had a signif...

Protective antibodies persist for months in surviv…

People who survive serious COVID-19 infections have long-lasting immune responses against the virus, according to a new study led by researchers at Massachusetts General ...